MirBSD manpage: mksh(1), pwd(1), rksh(1), sh(1), test(1), [(1)

MKSH(1)                      BSD Reference Manual                      MKSH(1)


     mksh, sh - MirBSD Korn shell


     mksh [-+abCefhiklmnprUuvXx] [-+o option] [-T [!]tty|-] [file [arg1 ...]]
     mksh [-+abCefhiklmnprUuvXx] [-+o option] [-T [!]tty|-] -c cmd [arg0 ...]
     mksh [-+abCefhiklmnprUuvXx] [-+o option] [-T [!]tty|-] -s [arg1 ...]
     builtin-name [argument ...]


     mksh is a command interpreter intended for both interactive and shell
     script use. Its command language is a superset of both sh(C) and POSIX
     shell language and largely compatible to the original Korn shell. At
     times, this manual page may give scripting advice; while it sometimes
     does take portable shell scripting or various standards into account all
     information is first and foremost presented with mksh in mind and should
     be taken as such.

I use Android, OS/2, etc. so what...?

     Please refer to: http://www.mirbsd.org/mksh-faq.htm#sowhatismksh


     Most builtins can be called directly, for example if a link or symlink(7)
     points to mksh, or if argv[0] is set correspondingly; this does not make
     sense for, or works properly with, all built-in utilities though.

     The options are as follows:

     -c  mksh will execute the command(s) contained in cmd, setting $0 to arg0
         (if present), $1 to the next argument, etc. If compiled with
         -DMKSH_MIDNIGHTBSD01ASH_COMPAT and in -o sh mode, a "--" argument
         directly following cmd is ignored for compatibility with the legacy
         FreeBSD sh; this is deprecated and may go away in the future.

     -i  Interactive shell. A shell that reads commands from standard input is
         "interactive" if this option is used or if both standard input and
         standard error are attached to a tty(4). An interactive shell has job
         control enabled, ignores the SIGINT, SIGQUIT and SIGTERM signals, and
         prints prompts before reading input (see the PS1 and PS2 parameters).
         It also processes the ENV parameter or the mkshrc file (see below).
         For non-interactive shells, the trackall option is on by default (see
         the set command below).

     -l  Login shell. If the name the shell is called as (i.e. argv[0]) or its
         basename begins with a dash (hyphen-minus) '-' or if this option is
         given, the shell is a "login shell"; see Startup files below.

     -p  Privileged shell. A shell is "privileged" if the real user ID from
         getuid(2) or group ID from getgid(2) does not match the effective
         user ID or group ID. Clearing the privileged option causes the shell
         to set its effective user ID and group ID to its initial real user ID
         and group ID, respectively. For further implications, see set -p and
         Startup files. If the shell is privileged and this flag is not set
         explicitly on invocation, nor during processing the startup files,
         the "privileged" flag is cleared automatically afterwards.

     -r  Restricted shell. A shell is "restricted" if the basename the shell
         is called with, after dash removal, begins with 'r' or if this option
         is used. The following restrictions come into effect after the shell
         processes any profile and ENV files:

         •   Command names cannot be specified with pathnames, either absolute
             or relative; the -p flag of the command built-in utility is not
             usable. The ENV, PATH and SHELL parameters cannot be changed.
         •   The current location is fixed: the cd builtin is disabled.
         •   Redirections that create files, i.e. ">", ">|", ">>" and "<>",
             cannot be used, and the HISTFILE parameter cannot be changed.

     -s  mksh will read and execute commands from standard input; all non-
         option arguments are assigned to the positional parameters.

     -T -
         Detach from the controlling terminal, return immediately (daemonise).

     -T [!]name
         Spawn mksh on the tty(4) device given. The paths name, /dev/ttyCname
         and /dev/ttyname are attempted in order. If name is prefixed with an
         exclamation mark ('!'), wait for the spawned shell to return, report
         its exit status or terminating signal visually. Exit 0 if spawned.

     In addition to the above, the flags [-+abCefhkmnUuvXx] and [-+o option],
     respectively for single-letter and long options, as described for the set
     built-in utility, can be used on the command line.

     If neither the -c nor the -s options are specified, mksh will read and
     execute commands as if the -s flag was passed iff the file argument is
     absent or "-"; otherwise, it sets $0 to file and reads commands from it.
     Further arguments arg1 ... are assigned to positional parameters.

     The exit status of the shell is 127 if the file specified on the command
     line could not be opened, or non-zero if a fatal error occurred during
     execution of the script. Otherwise, the errorlevel is that of the last
     command executed, 0 if no command was executed.

Startup files

     For the actual location of these files, see FILES. A login shell
     processes the system profile first. A privileged shell then processes the
     suid profile. A non-privileged login shell processes the user profile
     next. A non-privileged interactive shell checks the value of the ENV
     parameter after subjecting it to parameter, command, arithmetic and tilde
     ('~') substitution; if unset or empty, the user mkshrc profile is pro-
     cessed; otherwise, if a file whose name is the substitution result ex-
     ists, it is processed; non-existence is silently ignored. A privileged
     shell then drops privileges if neither was the -p option given on the
     command line nor set during execution of the startup files.

Command syntax

     The shell begins parsing its input by removing any backslash-newline com-
     binations, then breaking it into words. Words (which are sequences of
     characters) are delimited by unquoted whitespace characters (space, tab
     and newline) or meta-characters ('<', '>', '|', ';', '(', ')' and '&').
     Aside from delimiting words, spaces and tabs are ignored, while newlines
     usually delimit commands. The meta-characters are used in building the
     following tokens: "<", "<&", "<<", "<<<", ">", ">&", ">>", "&>", etc. are
     used to specify redirections (see Input/output redirection below); "|" is
     used to create pipelines; "|&" is used to create co-processes (see Co-
     processes below); ";" is used to separate commands; "&" is used to create
     asynchronous pipelines; "&&" and "||" are used to specify conditional ex-
     ecution; ";;", ";&" and ";|" are used in case statements; "(( ... ))" is
     used in arithmetic expressions; and lastly, "( ... )" is used to create

     Whitespace and meta-characters can be quoted individually using a
     backslash ('\'), or in groups using double ('"') or single ("'") quotes.
     Note that the following characters are also treated specially by the
     shell and must be quoted if they are to represent themselves: '\', '"',
     "'", '#', '$', '`', '~', '{', '}', '*', '?' and '['. The first three of
     these are the above mentioned quoting characters (see Quoting below);
     '#', if used at the beginning of a word, introduces a comment -
      everything after the '#' up to the nearest newline is ignored; '$' is
     used to introduce parameter, command and arithmetic substitutions (see
     Substitution below); '`' introduces an old-style command substitution
     (see Substitution below); '~' begins a directory expansion (see Tilde
     expansion below); '{' and '}' delimit csh(1)-style alternations (see
     Brace expansion below); and finally, '*', '?' and '[' are used in file
     name generation (see File name patterns below).

     As words and tokens are parsed, the shell builds commands, of which there
     are two basic types: simple-commands, typically programmes that are exe-
     cuted, and compound-commands, such as for and if statements, grouping
     constructs and function definitions.

     A simple-command consists of some combination of parameter assignments
     (see Parameters below), input/output redirections (see Input/output
     redirections below) and command words; the only restriction is that
     parameter assignments come before any command words. The command words,
     if any, define the command that is to be executed and its arguments. The
     command may be a shell built-in command, a function or an external com-
     mand (i.e. a separate executable file that is located using the PATH
     parameter; see Command execution below). Note that all command constructs
     have an exit status: for external commands, this is related to the status
     returned by wait(2) (if the command could not be found, the exit status
     is 127; if it could not be executed, the exit status is 126); the exit
     status of other command constructs (built-in commands, functions,
     compound-commands, pipelines, lists, etc.) are all well-defined and are
     described where the construct is described. The exit status of a command
     consisting only of parameter assignments is that of the last command sub-
     stitution performed during the parameter assignment or 0 if there were no
     command substitutions.

     Commands can be chained together using the "|" token to form pipelines,
     in which the standard output of each command but the last is piped (see
     pipe(2)) to the standard input of the following command. The exit status
     of a pipeline is that of its last command, unless the pipefail option is
     set (see there). All commands of a pipeline are executed in separate sub-
     shells; this is allowed by POSIX but differs from both variants of AT&T
     UNIX ksh, where all but the last command were executed in subshells; see
     the read builtin's description for implications and workarounds. A pipe-
     line may be prefixed by the "!" reserved word which causes the exit
     status of the pipeline to be logically complemented: if the original
     status was 0, the complemented status will be 1; if the original status
     was not 0, the complemented status will be 0.

     Lists of commands can be created by separating pipelines by any of the
     following tokens: "&&", "||", "&", "|&" and ";". The first two are for
     conditional execution: "cmd1 && cmd2" executes cmd2 only if the exit
     status of cmd1 is zero; "||" is the opposite - cmd2 is executed only if
     the exit status of cmd1 is non-zero. "&&" and "||" have equal precedence
     which is higher than that of "&", "|&" and ";", which also have equal
     precedence. Note that the "&&" and "||" operators are "left-associative".
     For example, both of these commands will print only "bar":

           $ false && echo foo || echo bar
           $ true || echo foo && echo bar

     The "&" token causes the preceding command to be executed asynchronously;
     that is, the shell starts the command but does not wait for it to com-
     plete (the shell does keep track of the status of asynchronous commands;
     see Job control below). When an asynchronous command is started when job
     control is disabled (i.e. in most scripts), the command is started with
     signals SIGINT and SIGQUIT ignored and with input redirected from
     /dev/null (however, redirections specified in the asynchronous command
     have precedence). The "|&" operator starts a co-process which is a spe-
     cial kind of asynchronous process (see Co-processes below). Note that a
     command must follow the "&&" and "||" operators, while it need not follow
     "&", "|&" or ";". The exit status of a list is that of the last command
     executed, with the exception of asynchronous lists, for which the exit
     status is 0.

     Compound commands are created using the following reserved words. These
     words are only recognised if they are unquoted and if they are used as
     the first word of a command (i.e. they can't be preceded by parameter as-
     signments or redirections):

           case     else     function     then      !       (
           do       esac     if           time      [[      ((
           done     fi       in           until     {
           elif     for      select       while     }

     In the following compound command descriptions, command lists (denoted as
     list) that are followed by reserved words must end with a semicolon, a
     newline or a (syntactically correct) reserved word. For example, the fol-
     lowing are all valid:

           $ { echo foo; echo bar; }
           $ { echo foo; echo bar<newline>}
           $ { { echo foo; echo bar; } }

     This is not valid:

           $ { echo foo; echo bar }

     case word in [[(] pattern [| pattern] ...) list <terminator>] ... esac
           The case statement attempts to match word against a specified
           pattern; the list associated with the first successfully matched
           pattern is executed. Patterns used in case statements are the same
           as those used for file name patterns except that the restrictions
           regarding '.' and '/' are dropped. Note that any unquoted space be-
           fore and after a pattern is stripped; any space within a pattern
           must be quoted. Both the word and the patterns are subject to
           parameter, command and arithmetic substitution, as well as tilde

           For historical reasons, open and close braces may be used instead
           of in and esac, for example: "case $foo { (ba[rz]|blah) date ;; }"

           The list <terminator>s are:

           ";;"  Terminate after the list.

           ";&"  Fall through into the next list.

           ";|"  Evaluate the remaining pattern-list tuples.

           The exit status of a case statement is that of the executed list;
           if no list is executed, the exit status is zero.

     for name [in word ...]; do list; done
           For each word in the specified word list, the parameter name is set
           to the word and list is executed. The exit status of a for state-
           ment is the last exit status of list; if list is never executed,
           the exit status is zero. If in is not used to specify a word list,
           the positional parameters ($1, $2, etc.) are used instead; in this
           case, use a newline instead of the semicolon (';') for portability.
           For historical reasons, open and close braces may be used instead
           of do and done, as in "for i; { echo $i; }" (not portable).

     function name { list; }
           Defines the function name (see Functions below). All redirections
           specified after a function definition are performed whenever the
           function is executed, not when the function definition is executed.

     name() command
           Mostly the same as function (see above and Functions below). Most
           amounts of space and tab after name will be ignored.

     function name() { list; }
           bashism for name() { list; } (the function keyword is ignored).

     if list; then list; [elif list; then list;] ... [else list;] fi
           If the exit status of the first list is zero, the second list is
           executed; otherwise, the list following the elif, if any, is exe-
           cuted with similar consequences. If all the lists following the if
           and elifs fail (i.e. exit with non-zero status), the list following
           the else is executed. The exit status of an if statement is that of
           whatever non-conditional (not the first) list that is executed; if
           no non-conditional list is executed, the exit status is zero.

     select name [in word ...]; do list; done
           The select statement provides an automatic method of presenting the
           user with a menu and selecting from it. An enumerated list of the
           specified words is printed on standard error, followed by a prompt
           (PS3: normally "#? "). A number corresponding to one of the
           enumerated words is then read from standard input, name is set to
           the selected word (or unset if the selection is not valid), REPLY
           is set to what was read (leading and trailing space is stripped),
           and list is executed. If a blank line (i.e. zero or more IFS oc-
           tets) is entered, the menu is reprinted without executing list.

           When list completes, the enumerated list is printed if REPLY is
           empty, the prompt is printed, and so on. This process continues un-
           til an end-of-file is read, an interrupt is received, or a break
           statement is executed inside the loop. The exit status of a select
           statement is zero if a break statement is used to exit the loop,
           non-zero otherwise. If "in word ..." is omitted, the positional
           parameters are used. For historical reasons, open and close braces
           may be used instead of do and done, as in: "select i; { echo $i; }"

     time [-p] [pipeline]
           The Command execution section describes the time reserved word.

     until list; do list; done
           This works like while (see below), except that the body list is ex-
           ecuted only while the exit status of the first list is non-zero.

     while list; do list; done
           A while is a pre-checked loop. Its body list is executed as often
           as the exit status of the first list is zero. The exit status of a
           while statement is the last exit status of the list in the body of
           the loop; if the body is not executed, the exit status is zero.

     [[ expression ]]
           Similar to the test and [ ... ] commands (described later), with
           the following exceptions:

           •   Field splitting and globbing are not performed on arguments.

           •   The -a (AND) and -o (OR) operators are replaced, respectively,
               with "&&" and "||".

           •   Operators (e.g. "-f", "=", "!") must be unquoted.

           •   Parameter, command and arithmetic substitutions are performed
               as expressions are evaluated and lazy expression evaluation is
               used for the "&&" and "||" operators. This means that in the
               following statement, $(<foo) is evaluated if and only if the
               file foo exists and is readable:

                     $ [[ -r foo && $(<foo) = b*r ]]

           •   The second operand of the "=" and "!=" expressions is a pattern
               (e.g. the comparison [[ foobar = f*r ]] succeeds). This even
               works indirectly, while quoting forces literal interpretation:

                     $ bar=foobar; baz='f*r'         # or: baz='f+(o)b?r'
                     $ [[ $bar = $baz ]]; echo $?    # 0
                     $ [[ $bar = "$baz" ]]; echo $?  # 1

     { list; }
           Compound construct; list is executed, but not in a subshell.
           Note that "{" and "}" are reserved words, not meta-characters.

           Execute list in a subshell, forking. There is no implicit way to
           pass environment changes from a subshell back to its parent.

     (( expression ))
           The arithmetic expression expression is evaluated; equivalent to
           'let "expression"' in a compound construct.
           See the let command and Arithmetic expressions below.


     Quoting is used to prevent the shell from treating characters or words
     specially. There are three methods of quoting. First, '\' quotes the fol-
     lowing character, unless it is at the end of a line, in which case both
     the '\' and the newline are stripped. Second, a single quote ("'") quotes
     everything up to the next single quote (this may span lines). Third, a
     double quote ('"') quotes all characters, except '$', '\' and '`', up to
     the next unescaped double quote. '$' and '`' inside double quotes have
     their usual meaning (i.e. parameter, arithmetic or command substitution)
     except no field splitting is carried out on the results of double-quoted
     substitutions, and the old-style form of command substitution has
     backslash-quoting for double quotes enabled. If a '\' inside a double-
     quoted string is followed by '"', '$', '\' or '`', only the '\' is re-
     moved, i.e. the combination is replaced by the second character; if it is
     followed by a newline, both the '\' and the newline are stripped; other-
     wise, both the '\' and the character following are unchanged.

     If a single-quoted string is preceded by an unquoted '$', C style
     backslash expansion (see below) is applied (even single quote characters
     inside can be escaped and do not terminate the string then); the expanded
     result is treated as any other single-quoted string. If a double-quoted
     string is preceded by an unquoted '$', the '$' is simply ignored.

Backslash expansion

     In places where backslashes are expanded, certain C and AT&T UNIX ksh or
     GNU bash style escapes are translated. These include "\a", "\b", "\f",
     "\n", "\r", "\t", "\U########", "\u####" and "\v". For "\U########" and
     "\u####", '#' means a hexadecimal digit (up to 4 or 8); these translate a
     Universal Coded Character Set codepoint to UTF-8 (see CAVEATS on UCS lim-
     itations). Furthermore, "\E" and "\e" expand to the escape character.

     In the print builtin mode, octal sequences must have the optional up to
     three octal digits '#' prefixed with the digit zero ("\0###"); hexade-
     cimal sequences "\x##" are limited to up to two hexadecimal digits '#';
     both octal and hexadecimal sequences convert to raw octets; "\%", where
     '%' is none of the above, translates to \% (backslashes are retained).

     In C style mode, raw octet-yielding octal sequences "\###" must not have
     the one up to three octal digits prefixed with the digit zero; hexade-
     cimal sequences "\x##" greedily eat up as many hexadecimal digits '#' as
     they can and terminate with the first non-xdigit; below \x100 these pro-
     duce raw octets; above, they are equivalent to "\U#". The sequence "\c%",
     where '%' is any octet, translates to Ctrl-%, that is, "\c?" becomes DEL,
     everything else is bitwise ANDed with 0x9F. "\%", where '%' is none of
     the above, translates to %: backslashes are trimmed even before newlines.


     There are two types of aliases: normal command aliases and tracked
     aliases. Command aliases are normally used as a short hand for a long or
     often used command. The shell expands command aliases (i.e. substitutes
     the alias name for its value) when it reads the first word of a command.
     An expanded alias is re-processed to check for more aliases. If a command
     alias ends in a space or tab, the following word is also checked for
     alias expansion. The alias expansion process stops when a word that is
     not an alias is found, when a quoted word is found, or when an alias word
     that is currently being expanded is found. Aliases are specifically an
     interactive feature: while they do happen to work in scripts and on the
     command line in some cases, aliases are expanded during lexing, so their
     use must be in a separate command tree from their definition; otherwise,
     the alias will not be found. Noticeably, command lists (separated by
     semicolon, in command substitutions also by newline) may be one same
     parse tree.

     The following command aliases are defined automatically by the shell:

           autoload='\\builtin typeset -fu'
           functions='\\builtin typeset -f'
           hash='\\builtin alias -t'
           history='\\builtin fc -l'
           integer='\\builtin typeset -i'
           local='\\builtin typeset'
           login='\\builtin exec login'
           nameref='\\builtin typeset -n'
           nohup='nohup '
           r='\\builtin fc -e -'
           type='\\builtin whence -v'

     Tracked aliases allow the shell to remember where it found a particular
     command. The first time the shell does a path search for a command that
     is marked as a tracked alias, it saves the full path of the command. The
     next time the command is executed, the shell checks the saved path to see
     that it is still valid, and if so, avoids repeating the path search.
     Tracked aliases can be listed and created using alias -t. Note that
     changing the PATH parameter clears the saved paths for all tracked
     aliases. If the trackall option is set (i.e. set -o trackall or set -h),
     the shell tracks all commands. This option is set automatically for non-
     interactive shells. For interactive shells, only the following commands
     are automatically tracked: cat(1), cc(1), chmod(1), cp(1), date(1),
     ed(1), emacs(1), grep(1), ls(1), make(1), mv(1), pr(1), rm(1), sed(1),
     sh(1), vi(1) and who(1).


     The first step the shell takes in executing a simple-command is to per-
     form substitutions on the words of the command. There are three kinds of
     substitution: parameter, command and arithmetic. Parameter substitutions,
     which are described in detail in the next section, take the form $name or
     ${name...}; arithmetic substitutions take the form $((expression)); and
     command substitutions take the form $(command) or (deprecated) `command`
     or (executed in the current environment) ${ command;} and evaluate to the
     output of command with any trailing newlines stripped. The latter form
     requires a space, tab or newline after the opening brace and that the
     closing brace be recognised as a keyword (i.e. is preceded by a newline
     or semicolon). They are also called funsubs (function substitutions) and
     behave similar to functions in that shell options are shared and local
     and return work, though, in contrast to valsubs (see below), exit does
     not terminate the parent shell for compatibility with AT&T UNIX ksh93.

     Another variant of substitution are the valsubs (value substitutions)
     ${|command;} which are also executed in the current environment, like
     funsubs, but share their I/O with the parent; instead, they evaluate to
     whatever the, initially empty, expression-local variable REPLY is set to
     within the commands; exit affects the parent like in a function call.

     If a substitution appears outside of double quotes, the results of the
     substitution are generally subject to word or field splitting according
     to the current value of the IFS parameter. The IFS parameter specifies a
     list of octets which are used to break a string up into several words;
     any octets from the set space, tab and newline that appear in the IFS oc-
     tets are called "IFS whitespace". Sequences of one or more IFS whitespace
     octets, in combination with zero or one non-IFS whitespace octets, delim-
     it a field. As a special case, leading and trailing IFS whitespace is
     stripped (i.e. no leading or trailing empty field is created by it);
     leading or trailing non-IFS whitespace does create an empty field.

     Example: If IFS is set to "<space>:" and VAR is set to
     "<space>A<space>:<space><space>B::D", the substitution for $VAR results
     in four fields: "A", "B", "" (an empty field) and "D". Note that if the
     IFS parameter is set to the empty string, no field splitting is done; if
     it is unset, the default value of space, tab and newline is used.

     Also, note that the field splitting applies only to the immediate result
     of the substitution. Using the previous example, the substitution for
     $VAR:E results in the fields: "A", "B", "" and "D:E", not "A", "B", "",
     "D" and "E". This behaviour is POSIX compliant but incompatible with some
     other shell implementations which do field splitting on the word which
     contained the substitution or use IFS as a general whitespace delimiter.

     The results of substitution are, unless otherwise specified, also subject
     to brace expansion and file name expansion (see the relevant sections

     A command substitution of the regular (comsub), deprecated, funsub or
     valsub form is replaced by the output generated by the specified command
     which is run in a subshell except for the funsub and valsub types which
     run in the current execution environment. For $(command), ${ command;}
     and ${|command;} forms, normal quoting rules are used when command is
     parsed; however, for the deprecated `command` form, a '\' followed by any
     of '$', '`' or '\' is stripped (as is '"' when the substitution is part
     of a double-quoted string); a backslash followed by any other character
     is unchanged. As a special case in command substitutions, a command of
     the form <file is interpreted to mean substitute the contents of file so
     that $(<foo) has the same effect, if foo is readable, as $(cat foo) but
     is much more performant.

     Note that some shells do not use a recursive parser for command substitu-
     tions, leading to failure for certain constructs; to be portable, use as
     workaround "x=$(cat) <<\EOF" (or the newline-keeping "x=<<\EOF" exten-
     sion) instead to merely slurp the string. IEEE Std 1003.1 ("POSIX.1")
     recommends using case statements of the form x=$(case $foo in (bar) echo
     $bar ;; (*) echo $baz ;; esac) instead, which would work but not serve as
     example for this portability issue.

           x=$(case $foo in bar) echo $bar ;; *) echo $baz ;; esac)
           # above fails to parse on old shells; below is the workaround
           x=$(eval $(cat)) <<\EOF
           case $foo in bar) echo $bar ;; *) echo $baz ;; esac

     Arithmetic substitutions are replaced by the value of the specified ex-
     pression. For example, the command print $((2+3*4)) displays 14. See
     Arithmetic expressions for a description of an expression.


     Parameters are shell variables; they can be assigned values, and their
     values can be accessed using a parameter substitution. A parameter name
     is either one of the special single punctuation character or positional
     parameters described below, or a letter followed by zero or more letters,
     digits or underscores. The latter form can be accessed as array appending
     an index of the form [expr] (in which expr is an arithmetic expression).
     Array indices range from 0 to 4294967295 (2^32-1), inclusive, in mksh.

     Parameter substitutions take the form $name, ${name} or ${name[expr]}
     where name is a parameter name. Substitutions of an array in scalar con-
     text, i.e. without an expr in the latter form mentioned above, expand the
     element with the key "0". Substitution of all array elements with
     ${name[*]} and ${name[@]} works equivalent to $* and $@ for positional
     parameters. If substitution is performed on a parameter (or an array
     parameter element) that is not set, an empty string is substituted unless
     the nounset option (set -u) is set, in which case an error occurs.

     Parameters can be assigned values in a number of ways. First, the shell
     implicitly sets some parameters like "#", "PWD" and "$"; this is the only
     way the special single character parameters are set. Second, parameters
     are imported from the shell's environment at startup. Third, parameters
     can be assigned values on the command line: for example, FOO=bar sets the
     parameter "FOO" to "bar"; multiple parameter assignments can be given on
     a single command line and they can be followed by a simple-command, in
     which case the assignments are in effect only for the duration of the
     command (such assignments are also exported; see below for the implica-
     tions of this). Note that both the parameter name and the '=' must be un-
     quoted for the shell to recognise a parameter assignment. The construct
     FOO+=baz is also recognised; the old and new values are string-
     concatenated with no separator. The fourth way of setting a parameter is
     with the export, readonly and typeset commands; see their descriptions in
     the Command execution section. Fifth, for and select loops set parameters
     as well as the getopts, read and set -A commands. Lastly, parameters can
     be assigned values using assignment operators inside arithmetic expres-
     sions (see Arithmetic expressions below) or using the ${name=value} form
     of the parameter substitution (see below).

     Parameters with the export attribute (set using the export or typeset -x
     commands, or by parameter assignments followed by simple commands) are
     put in the environment (see environ(7)) of commands run by the shell as
     name=value pairs. When the shell starts up, it extracts parameters and
     their values from its environment setting the export attribute for those.

     Modifiers can be applied to the ${name} form of parameter substitution:

             If name is set and not empty, it is substituted; otherwise, word
             is substituted.

             If name is set and not empty, word is substituted; otherwise,
             nothing is substituted.

             If name is set and not empty, it is substituted; otherwise, it is
             assigned word and the resulting value of name is substituted.

             If name is set and not empty, it is substituted; otherwise, word
             is printed on standard error (preceded by name:) and an error oc-
             curs (normally causing termination of a shell script, function,
             or a script sourced using the "." built-in). If word is omitted,
             the string "parameter null or not set" is used instead.

     Note that, for all of the above, word is actually considered quoted, and
     special parsing rules apply. The parsing rules also differ on whether the
     expression is double-quoted: word then uses double-quoting rules, except
     for the double quote itself ('"') and the closing brace, which, if
     backslash escaped, gets quote removal applied.

     In the above modifiers, the ':' can be omitted, in which case the condi-
     tions only depend on name being set (as opposed to set and not empty). If
     word is needed, parameter, command, arithmetic and tilde substitution are
     performed on it; if word is not needed, it is not evaluated.

     The following forms of parameter substitution can also be used:

             The number of positional parameters if name is "*", "@" or not
             specified; otherwise the length (in characters) of the string
             value of parameter name.

             The number of elements in the array name.

             The width (in screen columns) of the string value of parameter
             name, or -1 if ${name} contains a control character.

             The name of the variable referred to by name. This will be name
             except when name is a name reference (bound variable), created by
             the nameref command (which is an alias for typeset -n). name can-
             not be one of most special parameters (see below).

             The names of indices (keys) in the array name.

             If pattern matches the beginning of the value of parameter name,
             the matched text is deleted from the result of substitution. A
             single '#' results in the shortest match, and two of them result
             in the longest match.

             Like ${...#...} but deletes from the end of the value.

             The longest match of pattern in the value of parameter name is
             replaced with string (deleted if string is empty; the trailing
             slash ('/') may be omitted in that case). A leading slash fol-
             lowed by '#' or '%' causes the pattern to be anchored at the be-
             ginning or end of the value, respectively; empty unanchored
             patterns cause no replacement; a single leading slash or use of a
             pattern that matches the empty string causes the replacement to
             happen only once; two leading slashes cause all occurrences of
             matches in the value to be replaced. May be slow on long strings.

             The same as ${name//pattern/string}, except that both pattern and
             string are expanded anew for each iteration. Use with KSH_MATCH.

             The first len characters of name, starting at position pos, are
             substituted. Both pos and :len are optional. If pos is negative,
             counting starts at the end of the string; if it is omitted, it
             defaults to 0. If len is omitted or greater than the length of
             the remaining string, all of it is substituted. Both pos and len
             are evaluated as arithmetic expressions.

             The hash (using the BAFH1-0 algorithm) of the expansion of name.
             This is also used internally for the shell's hashtables.

             A quoted expression safe for re-entry, whose value is the value
             of the name parameter, is substituted.

             The value of name in extended caret notation, with both caret
             ('^') and backslash ('\') backslash-escaped to avoid ambiguity.

     Note that pattern may need extended globbing pattern (@(...)), single
     ('...') or double ("...") quote escaping unless -o sh is set.

     The following special parameters are implicitly set by the shell and can-
     not be set directly using assignments:

     !       Process ID of the last background process started. If no back-
             ground processes have been started, the parameter is not set.

     #       The number of positional parameters ($1, $2, etc.).

     $       The PID of the shell or, if it is a subshell, the PID of the ori-
             ginal shell. Do NOT use this mechanism for generating temporary
             file names; see mktemp(1) instead.

     -       The concatenation of the current single letter options (see the
             set command below for a list of options).

     ?       The exit status of the last non-asynchronous command executed. If
             the last command was killed by a signal, $? is set to 128 plus
             the signal number, but at most 255.

     0       The name of the shell, determined as follows: the first argument
             to mksh if it was invoked with the -c option and arguments were
             given; otherwise the file argument, if it was supplied; or else
             the name the shell was invoked with (i.e. argv[0]). $0 is also
             set to the name of the current script, or to the name of the
             current function if it was defined with the function keyword
             (i.e. a Korn shell style function).

     1 .. 9  The first nine positional parameters that were supplied to the
             shell, function, or script sourced using the "." ("dot") builtin.
             Further positional parameters may be accessed using ${number}.

     *       All positional parameters (except 0), i.e. $1, $2, $3, ...
             If used outside of double quotes, parameters are separate words
             (which are subjected to word splitting); if used within double
             quotes, parameters are separated by the first character of the
             IFS parameter (or the empty string if IFS is unset.

     @       Same as $*, unless it is used inside double quotes, in which case
             a separate word is generated for each positional parameter. If
             there are no positional parameters, no word is generated. "$@"
             can be used to access arguments, verbatim, without losing empty
             arguments or splitting arguments with spaces (IFS, actually).

     The following parameters are set and/or used by the shell:

     _            (underscore) When an external command is executed by the
                  shell, this parameter is set in the environment of the new
                  process to the path of the executed command. In interactive
                  use, this parameter is also set in the parent shell to the
                  last word of the previous command.

     BASHPID      The PID of the shell or subshell.

     CDPATH       Like PATH, but used to resolve the argument to the cd built-
                  in command. Note that if CDPATH is set and does not contain
                  "." or an empty string element, the current directory is not
                  searched. Also, the cd built-in command will display the
                  resulting directory when a match is found in any search path
                  other than the empty path.

     COLUMNS      Set to the number of columns on the terminal or window. If
                  never unset and not imported, always set dynamically; unless
                  the value as reported by stty(1) is non-zero and sane enough
                  (minimum is 12x3), defaults to 80; similar for LINES. This
                  parameter is used by the interactive line editing modes and
                  by the select, set -o and kill -l commands to format infor-
                  mation columns. Importing from the environment or unsetting
                  this parameter removes the binding to the actual terminal
                  size in favour of the provided value.

     ENV          If this parameter is found to be set after any profile files
                  are executed, the expanded value is used as a shell startup
                  file. It typically contains function and alias definitions.

                  Time since the epoch, as returned by gettimeofday(2), for-
                  matted as decimal tv_sec followed by a dot ('.') and tv_usec
                  padded to exactly six decimal digits.

     EXECSHELL    If set, this parameter is assumed to contain the shell that
                  is to be used to execute commands that execve(2) fails to
                  execute and which do not start with a "#!shell" sequence.

     FCEDIT       The editor used by the fc command (see below).

     FPATH        Like PATH, but used when an undefined function is executed
                  to locate the file defining the function. It is also
                  searched when a command can't be found using PATH. See
                  Functions below for more information.

     HISTFILE     The name of the file used to store command history. When as-
                  signed to or unset, the file is opened, history is truncated
                  then loaded from the file; subsequent new commands (possibly
                  consisting of several lines) are appended once they success-
                  fully compiled. Also, several invocations of the shell will
                  share history if their HISTFILE parameters all point to the
                  same file.

                  Note: If HISTFILE is unset or empty, no history file is
                  used. This is different from AT&T UNIX ksh.

     HISTSIZE     The number of commands normally stored for history. The de-
                  fault is 2047. The maximum is 65535.

     HOME         The default directory for the cd command and the value sub-
                  stituted for an unqualified ~ (see Tilde expansion below).

     IFS          Internal field separator, used during substitution and by
                  the read command, to split values into distinct arguments;
                  normally set to space, tab and newline. See Substitution
                  above for details.

                  Note: This parameter is not imported from the environment
                  when the shell is started.

     KSHEGID      The effective group id of the shell at startup.

     KSHGID       The real group id of the shell at startup.

     KSHUID       The real user id of the shell at startup.

     KSH_MATCH    The last matched string. In a future version, this will be
                  an indexed array, with indexes 1 and up capturing matching
                  groups. Set by string comparisons (= and !=) in double-
                  bracket test expressions when a match is found (when != re-
                  turns false), by case when a match is encountered, and by
                  the substitution operations ${x#pat}, ${x##pat}, ${x%pat},
                  ${x%%pat}, ${x/pat/rpl}, ${x/#pat/rpl}, ${x/%pat/rpl},
                  ${x//pat/rpl}, and ${x@/pat/rpl}. See the end of the Emacs
                  editing mode documentation for an example.

     KSH_VERSION  The name (self-identification) and version of the shell
                  (read-only). See also the version commands in Emacs editing
                  mode and Vi editing mode sections, below.

     LINENO       The line number of the function or shell script that is
                  currently being executed.

     LINES        Set to the number of lines on the terminal or window. De-
                  faults to 24; always set, unless imported or unset. See

     OLDPWD       The previous working directory. Unset if cd has not success-
                  fully changed directories since the shell started or if the
                  shell doesn't know where it is.

     OPTARG       When using getopts, it contains the argument for a parsed
                  option, if it requires one.

     OPTIND       The index of the next argument to be processed when using
                  getopts. Assigning 1 to this parameter causes getopts to
                  process arguments from the beginning the next time it is in-

     PATH         A colon (semicolon on OS/2) separated list of directories
                  that are searched when looking for commands and files
                  sourced using the "." command (see below). An empty string
                  resulting from a leading or trailing (semi)colon, or two ad-
                  jacent ones, is treated as a "." (the current directory).

     PATHSEP      A colon (semicolon on OS/2), for the user's convenience.

     PGRP         The process ID of the shell's process group leader.

     PIPESTATUS   An array containing the errorlevel (exit status) codes, one
                  by one, of the last pipeline run in the foreground.

     PPID         The process ID of the shell's parent.

     PS1          The primary prompt for interactive shells. Parameter, com-
                  mand and arithmetic substitutions are performed, and '!' is
                  replaced with the current command number (see the fc command
                  below). A literal '!' can be put in the prompt by placing
                  "!!" in PS1.

                  The default prompt is "$ " for non-root users, "# " for
                  root. If mksh is invoked by root and PS1 does not contain a
                  '#' character, the default value will be used even if PS1
                  already exists in the environment.

                  The mksh distribution comes with a sample dot.mkshrc con-
                  taining a sophisticated example, but you might like the fol-
                  lowing one (note that ${HOSTNAME:=$(hostname)} and the root-
                  vs-user distinguishing clause are (in this example) executed
                  at PS1 assignment time, while the $USER and $PWD are escaped
                  and thus will be evaluated each time a prompt is displayed):

                  PS1='${USER:=$(id -un)}'"@${HOSTNAME:=$(hostname)}:\$PWD $(
                          if (( USER_ID )); then print \$; else print \#; fi) "

                  Note that since the command-line editors try to figure out
                  how long the prompt is (so they know how far it is to the
                  edge of the screen), escape codes in the prompt tend to mess
                  things up. You can tell the shell not to count certain se-
                  quences (such as escape codes) by prefixing your prompt with
                  a character (such as Ctrl-A) followed by a carriage return
                  and then delimiting the escape codes with this character.
                  Any occurrences of that character in the prompt are not
                  printed. By the way, don't blame me for this hack; it's
                  derived from the original ksh88(1), which did print the del-
                  imiter character so you were out of luck if you did not have
                  any non-printing characters.

                  Since backslashes and other special characters may be inter-
                  preted by the shell, to set PS1 either escape the backslash
                  itself or use double quotes. The latter is more practical.
                  This is a more complex example, avoiding to directly enter
                  special characters (for example with ^V in the emacs editing
                  mode), which embeds the current working directory, in re-
                  verse video (colour would work, too), in the prompt string:

                        x=$(print \\001) # otherwise unused char
                        PS1="$x$(print \\r)$x$(tput so)$x\$PWD$x$(tput se)$x> "

                  Due to a strong suggestion from David G. Korn, mksh now also
                  supports the following form:

                        PS1=$'\1\r\1\e[7m\1$PWD\1\e[0m\1> '

     PS2          Secondary prompt string, by default "> ", used when more in-
                  put is needed to complete a command.

     PS3          Prompt used by the select statement when reading a menu
                  selection. The default is "#? ".

     PS4          Used to prefix commands that are printed during execution
                  tracing (see the set -x command below). Parameter, command
                  and arithmetic substitutions are performed before it is
                  printed. The default is "+ ". You may want to set it to
                  "[$EPOCHREALTIME] " instead, to include timestamps.

     PWD          The current working directory. May be unset or empty if the
                  shell doesn't know where it is.

     RANDOM       Each time RANDOM is referenced, it is assigned a number
                  between 0 and 32767 from a Linear Congruential PRNG first.

     REPLY        Default parameter for the read command if no names are
                  given. Also used in select loops to store the value that is
                  read from standard input.

     SECONDS      The number of seconds since the shell started or, if the
                  parameter has been assigned an integer value, the number of
                  seconds since the assignment plus the value that was as-

     TMOUT        If set to a positive integer in an interactive shell, it
                  specifies the maximum number of seconds the shell will wait
                  for input after printing the primary prompt (PS1). If the
                  time is exceeded, the shell exits.

     TMPDIR       The directory temporary shell files are created in. If this
                  parameter is not set or does not contain the absolute path
                  of a writable directory, temporary files are created in

     USER_ID      The effective user id of the shell at startup.

Tilde expansion

     Tilde expansion, which is done in parallel with parameter substitution,
     is applied to words starting with an unquoted '~'. In parameter assign-
     ments (such as those preceding a simple-command or those occurring in the
     arguments of a declaration utility), tilde expansion is done after any
     assignment (i.e. after the equals sign) or after an unquoted colon (':');
     login names are also delimited by colons. The Korn shell, except in POSIX
     mode, always expands tildes after unquoted equals signs, not just in as-
     signment context (see below), and enables tab completion for tildes after
     all unquoted colons during command line editing.

     The characters following the tilde, up to the first '/', if any, are as-
     sumed to be a login name. If the login name is empty, '+' or '-', the
     simplified value of the HOME, PWD or OLDPWD parameter is substituted,
     respectively. Otherwise, the password file is searched for the login
     name, and the tilde expression is substituted with the user's home direc-
     tory. If the login name is not found in the password file or if any quot-
     ing or parameter substitution occurs in the login name, no substitution
     is performed.

     The home directory of previously expanded login names are cached and re-
     used. The alias -d command may be used to list, change and add to this
     cache (e.g. alias -d fac=/usr/local/facilities; cd ~fac/bin).

Brace expansion (alternation)

     Brace expressions take the following form:


     The expressions are expanded to N words, each of which is the concatena-
     tion of prefix, stri and suffix (e.g. "a{c,b{X,Y},d}e" expands to four
     words: "ace", "abXe", "abYe" and "ade"). As noted in the example, brace
     expressions can be nested and the resulting words are not sorted. Brace
     expressions must contain an unquoted comma (',') for expansion to occur
     (e.g. {} and {foo} are not expanded). Brace expansion is carried out
     after parameter substitution and before file name generation.

File name patterns

     A file name pattern is a word containing one or more unquoted '?', '*',
     '+', '@' or '!' characters or "[...]" sequences. Once brace expansion has
     been performed, the shell replaces file name patterns with the sorted
     names of all the files that match the pattern (if no files match, the
     word is left unchanged). The pattern elements have the following meaning:

     ?       Matches any single character.

     *       Matches any sequence of octets.

     [...]   Matches any of the octets inside the brackets. Ranges of octets
             can be specified by separating two octets by a '-' (e.g. "[a0-9]"
             matches the letter 'a' or any digit). Character classes can be
             specified by wrapping the name of the class between "[:" and ":]"
             (e.g. "[[:alpha:][:digit:].]" matches any ASCII letter or digit
             and the full stop).

             In order to represent itself, a '-' must either be quoted or the
             first or last octet in the octet list. Similarly, if it is to
             represent itself instead of the end of the list, a ']' must be
             quoted or the first octet in the list. Also, an '!' appearing at
             the start of the list has special meaning (see below), so to
             represent itself it must be quoted or appear later in the list.
             '^' at the beginning of the list must be quoted or appear later.

     [!...]  Like [...], except it matches any octet not inside the brackets.

             Matches any string of octets that matches zero or more oc-
             currences of the specified patterns. Example: The pattern
             *(foo|bar) matches the strings "", "foo", "bar", "foobarfoo",

             Matches any string of octets that matches one or more occurrences
             of the specified patterns. Example: The pattern +(foo|bar)
             matches the strings "foo", "bar", "foobar", etc.

             Matches the empty string or a string that matches one of the
             specified patterns. Example: The pattern ?(foo|bar) only matches
             the strings "", "foo" and "bar".

             Matches a string that matches one of the specified patterns. Ex-
             ample: The pattern @(foo|bar) only matches the strings "foo" and

             Matches any string that does not match one of the specified pat-
             terns. Examples: The pattern !(foo|bar) matches all strings ex-
             cept "foo" and "bar"; the pattern !(*) matches no strings; the
             pattern !(?)* matches all strings (think about it).

     The following character classes are supported (note all POSIX references
     assume the C locale; EBCDIC systems use the bytes from the codepage that
     map to the named ASCII characters so e.g. "[[:upper:]]" is correct while
     "[A-Z]" will contain probably-unwanted characters on EBCDIC systems):

           <         (BSD) the null string at the beginning of a word
           >         (BSD) the null string at the end of a word
           alnum     (POSIX) alphanumerical (alpha or digit)
           alpha     (POSIX) alphabetical (upper or lower)
           ascii     (GNU bash) any 7-bit ASCII character except NUL
           blank     (POSIX) space or horizontal tab
           cntrl     (POSIX) ASCII C0 control characters (\x00-\x1F) or \x7F
           digit     (POSIX) ASCII decimal digits (0-9)
           graph     (POSIX) alnum or punct (!-~)
           lower     (POSIX) ASCII lowercase letters (a-z)
           print     (POSIX) space or graph (\x20-~)
           punct     (POSIX) punctuation (graph except alnum):
           sh_alias  (mksh) valid in alias names: alnum or !%+,-.:@[]_
           sh_edq    (mksh) quoted by tab completion: "#$&'()*:;<=>?[\\`{|}~
           sh_ifs    (mksh) IFS whitespace, IFS non-whitespace, NUL (via $IFS)
           sh_ifsws  (mksh) IFS WS candidates: space, horizontal tab, linefeed
           sh_nl     (mksh) linefeed or (OS/2 TEXTMODE only) carriage return
           sh_quote  (mksh) characters requiring quoting, minus space:
           space     (POSIX) horizontal tab, line feed, vertical tab,
                     form feed, carriage return, space (\x09-\x0D\x20)
           upper     (POSIX) ASCII uppercase letters (A-Z)
           word      (GNU bash) alphanumerical (alnum) or underscore ("_")
           xdigit    (POSIX) hexadecimal digits (0-9A-Fa-f) a.k.a. nybbles

     Note that complicated globbing, especially with alternatives, is slow;
     using separate comparisons may (or may not) be faster.

     Note that mksh (and pdksh) never matches "." and "..", but AT&T UNIX ksh,
     Bourne sh and GNU bash do.

     Note that none of the above pattern elements match either a period ('.')
     at the start of a file name or a slash ('/'), even if they are explicitly
     used in a [...] sequence; also, the names "." and ".." are never matched,
     even by the pattern ".*".

     If the markdirs option is set, any directories that result from file name
     generation are marked with a trailing '/'.

Input/output redirection

     When a command is executed, its standard input, standard output and stan-
     dard error (file descriptors 0, 1 and 2, respectively) are normally in-
     herited from the shell. Three exceptions to this are commands in pipe-
     lines, for which standard input and/or standard output are those set up
     by the pipeline, asynchronous commands created when job control is dis-
     abled, for which standard input is initially set to /dev/null, and com-
     mands for which any of the following redirections have been specified:

     >file       Standard output is redirected to file. If file does not ex-
                 ist, it is created; if it does exist, is a regular file, and
                 the noclobber option is set, an error occurs; otherwise, the
                 file is truncated. Note that this means the command cmd <foo
                 >foo will open foo for reading and then truncate it when it
                 opens it for writing, before cmd gets a chance to actually
                 read foo.

     >|file      Same as >, except the file is truncated, even if the
                 noclobber option is set.

     >>file      Same as >, except if file exists it is appended to instead of
                 being truncated. Also, the file is opened in append mode, so
                 writes always go to the end of the file (see open(2)).

     <file       Standard input is redirected from file, which is opened for

     <>file      Same as <, except the file is opened for reading and writing.

     <<marker    After reading the command line containing this kind of
                 redirection (called a "here document"), the shell copies
                 lines from the command source into a temporary file until a
                 line matching marker is read. When the command is executed,
                 standard input is redirected from the temporary file. If
                 marker contains no quoted characters, the contents of the
                 temporary file are processed as if enclosed in double quotes
                 each time the command is executed, so parameter, command and
                 arithmetic substitutions are performed, along with backslash
                 ('\') escapes for '$', '`', '\' and "\newline", but not for
                 '"'. If multiple here documents are used on the same command
                 line, they are saved in order.

                 If no marker is given, the here document ends at the next <<
                 and substitution will be performed. If marker is only a set
                 of either single "''" or double '""' quotes with nothing in
                 between, the here document ends at the next empty line and
                 substitution will not be performed.

     <<-marker   Same as <<, except leading tabs are stripped from lines in
                 the here document.

     <<<word     Same as <<, except that word is the here document. This is
                 called a here string.

     <&fd        Standard input is duplicated from file descriptor fd. fd can
                 be a single digit, indicating the number of an existing file
                 descriptor; the letter 'p', indicating the file descriptor
                 associated with the output of the current co-process; or the
                 character '-', indicating standard input is to be closed.

     >&fd        Same as <&, except the operation is done on standard output.

     &>file      Same as >file 2>&1. This is a deprecated (legacy) GNU bash
                 extension supported by mksh which also supports the preceding
                 explicit fd digit, for example, 3&>file is the same as 3>file
                 2>&3 in mksh but a syntax error in GNU bash.

     &>|file, &>>file, &>&fd
                 Same as >|file, >>file or >&fd, followed by 2>&1, as above.
                 These are mksh extensions.

     In any of the above redirections, the file descriptor that is redirected
     (i.e. standard input or standard output) can be explicitly given by
     preceding the redirection with a single digit. Parameter, command and ar-
     ithmetic substitutions, tilde substitutions, and, if the shell is in-
     teractive, file name generation are all performed on the file, marker and
     fd arguments of redirections. Note, however, that the results of any file
     name generation are only used if a single file is matched; if multiple
     files match, the word with the expanded file name generation characters
     is used. Note that in restricted shells, redirections which can create
     files cannot be used.

     For simple-commands, redirections may appear anywhere in the command; for
     compound-commands (if statements, etc.), any redirections must appear at
     the end. Redirections are processed after pipelines are created and in
     the order they are given, so the following will print an error with a
     line number prepended to it:

           $ cat /foo/bar 2>&1 >/dev/null | pr -n -t

     File descriptors created by I/O redirections are private to the shell.

Arithmetic expressions

     Integer arithmetic expressions can be used with the let command, inside
     $((...)) expressions, inside array references (e.g. name[expr]), as
     numeric arguments to the test command, and as the value of an assignment
     to an integer parameter. Warning: This also affects implicit conversion
     to integer, for example as done by the let command. Never use unchecked
     user input, e.g. from the environment (although the shell tracks import
     status and refuses to automatically coerce those), in arithmetic context!

     Expressions are calculated using signed arithmetic and the mksh_ari_t
     type (a 32-bit signed integer), unless they begin with a sole '#' charac-
     ter, in which case they use mksh_uari_t (a 32-bit unsigned integer).

     Expressions may contain alpha-numeric parameter identifiers, array refer-
     ences and integer constants and may be combined with the following C
     operators (listed and grouped in increasing order of precedence):

     Unary operators:

           + - ! ~ ++ --

     Binary operators:

           = += -= *= /= %= <<= >>= ^<= ^>= &= ^= |=
           == !=
           < <= > >=
           << >> ^< ^>
           + -
           * / %

     Ternary operators:

           ?: (precedence is immediately higher than assignment)

     Grouping operators:

           ( )

     Integer constants and expressions are calculated using an exactly 32-bit
     wide, signed (two's complement) or unsigned, type with silent wraparound
     on integer overflow. Integer constants may be specified with arbitrary
     bases using the notation base#number, where base is a decimal integer
     specifying the base (up to 36), and number is a number in the specified
     base. Additionally, base-16 integers may be specified by prefixing with
     "0x" (case-insensitive) in all forms of arithmetic expressions, except as
     numeric arguments to the test built-in utility. Prefixing numbers with a
     sole digit zero ("0") does not cause interpretation as octal (except in
     POSIX mode, as required by the standard), as that's unsafe. Prefixing
     with "10#" forces interpretation as decimal, even with leading zeros. An
     unset or empty parameter evaluates to 0 in integer context.

     As a special mksh extension, numbers to the base of one are treated as
     either (8-bit transparent) ASCII or Universal Coded Character Set
     codepoints, depending on the shell's utf8-mode flag (current setting).
     The AT&T UNIX ksh93 syntax of "'x'" instead of "1#x" is also supported.
     Note that NUL bytes (integral value of zero) cannot be used. If 'x' isn't
     comprised of exactly one valid character, the behaviour is undefined
     (usually, the shell aborts with a parse error, but rarely, it succeeds,
     e.g. on the sequence C2 20); users of this feature (as opposed to read
     -a) must validate the input first. See CAVEATS for UTF-8 mode handling.
     Base-1 integers don't work well with a number of other shell features,
     such as reentry-safe output; use print -A or read -a if possible.

     The operators are evaluated as follows:

           unary +
                   Result is the argument (included for completeness).

           unary -

           !       Logical NOT; the result is 1 if argument is zero, 0 if not.

           ~       Arithmetic (bit-wise) NOT.

           ++      Increment; must be applied to a parameter (not a literal or
                   other expression). The parameter is incremented by 1. When
                   used as a prefix operator, the result is the incremented
                   value of the parameter; when used as a postfix operator,
                   the result is the original value of the parameter.

           --      Similar to ++, except the parameter is decremented by 1.

           ,       Separates two arithmetic expressions; the left-hand side is
                   evaluated first, then the right. The result is the value of
                   the expression on the right-hand side.

           =       Assignment; the variable on the left is set to the value on
                   the right.

           += -= *= /= %= <<= >>= ^<= ^>= &= ^= |=
                   Assignment operators. <var><op>=<expr> is the same as
                   <var>=<var><op><expr>, with any operator precedence in
                   <expr> preserved. For example, "var1 *= 5 + 3" is the same
                   as specifying "var1 = var1 * (5 + 3)".

           ||      Logical OR; the result is 1 if either argument is non-zero,
                   0 if not. The right argument is evaluated only if the left
                   argument is zero.

           &&      Logical AND; the result is 1 if both arguments are non-
                   zero, 0 if not. The right argument is evaluated only if the
                   left argument is non-zero.

           |       Arithmetic (bit-wise) OR.

           ^       Arithmetic (bit-wise) XOR (exclusive-OR).

           &       Arithmetic (bit-wise) AND.

           ==      Equal; the result is 1 if both arguments are equal, 0 if

           !=      Not equal; the result is 0 if both arguments are equal, 1
                   if not.

           <       Less than; the result is 1 if the left argument is less
                   than the right, 0 if not.

           <= > >=
                   Less than or equal, greater than, greater than or equal.
                   See <.

           << >>   Shift left (right); the result is the left argument with
                   its bits arithmetically (signed operation) or logically
                   (unsigned expression) shifted left (right) by the amount
                   given in the right argument.

           ^< ^>   Rotate left (right); the result is similar to shift, except
                   that the bits shifted out at one end are shifted in at the
                   other end, instead of zero or sign bits.

           + - * /
                   Addition, subtraction, multiplication and division.

           %       Remainder; the result is the symmetric remainder of the
                   division of the left argument by the right. To get the
                   mathematical modulus of "a mod b", use the formula
                   "(a % b + b) % b".

                   If <arg1> is non-zero, the result is <arg2>; otherwise the
                   result is <arg3>. The non-result argument is not evaluated.


     A co-process (which is a pipeline created with the "|&" operator) is an
     asynchronous process that the shell can both write to (using print -p)
     and read from (using read -p). The input and output of the co-process can
     also be manipulated using >&p and <&p redirections, respectively. Once a
     co-process has been started, another can't be started until the co-
     process exits, or until the co-process's input has been redirected using
     an exec n>&p redirection. If a co-process's input is redirected in this
     way, the next co-process to be started will share the output with the
     first co-process, unless the output of the initial co-process has been
     redirected using an exec n<&p redirection.

     Some notes concerning co-processes:

     •   The only way to close the co-process's input (so the co-process reads
         an end-of-file) is to redirect the input to a numbered file descrip-
         tor and then close that file descriptor: exec 3>&p; exec 3>&-

     •   In order for co-processes to share a common output, the shell must
         keep the write portion of the output pipe open. This means that end-
         of-file will not be detected until all co-processes sharing the co-
         process's output have exited (when they all exit, the shell closes
         its copy of the pipe). This can be avoided by redirecting the output
         to a numbered file descriptor (as this also causes the shell to close
         its copy). Note that this behaviour is slightly different from the
         original Korn shell which closes its copy of the write portion of the
         co-process output when the most recently started co-process (instead
         of when all sharing co-processes) exits.

     •   print -p will ignore SIGPIPE signals during writes if the signal is
         not being trapped or ignored; the same is true if the co-process in-
         put has been duplicated to another file descriptor and print -un is


     Functions are defined using either Korn shell function function-name syn-
     tax or the Bourne/POSIX shell function-name() syntax (see below for the
     difference between the two forms). Functions are like .-scripts (i.e.
     scripts sourced using the "." built-in) in that they are executed in the
     current environment. However, unlike .-scripts, shell arguments (i.e. po-
     sitional parameters $1, $2, etc.) are never visible inside them. When the
     shell is determining the location of a command, functions are searched
     after special built-in commands, before builtins and the PATH is

     An existing function may be deleted using unset -f function-name. A list
     of functions can be obtained using typeset +f and the function defini-
     tions can be listed using typeset -f. The autoload command (which is an
     alias for typeset -fu) may be used to create undefined functions: when an
     undefined function is executed, the shell searches the path specified in
     the FPATH parameter for a file with the same name as the function which,
     if found, is read and executed. If after executing the file the named
     function is found to be defined, the function is executed; otherwise, the
     normal command search is continued (i.e. the shell searches the regular
     built-in command table and PATH). Note that if a command is not found us-
     ing PATH, an attempt is made to autoload a function using FPATH (this is
     an undocumented feature of the original Korn shell).

     Functions can have two attributes, "trace" and "export", which can be set
     with typeset -ft and typeset -fx, respectively. When a traced function is
     executed, the shell's xtrace option is turned on for the function's dura-
     tion. The "export" attribute of functions is currently not used.

     Since functions are executed in the current shell environment, parameter
     assignments made inside functions are visible after the function com-
     pletes. If this is not the desired effect, the typeset command can be
     used inside a function to create a local parameter. Note that AT&T UNIX
     ksh93 uses static scoping (one global scope, one local scope per func-
     tion) and allows local variables only on Korn style functions, whereas
     mksh uses dynamic scoping (nested scopes of varying locality). Note that
     special parameters (e.g. $$, $!) can't be scoped in this way.

     The exit status of a function is that of the last command executed in the
     function. A function can be made to finish immediately using the return
     command; this may also be used to explicitly specify the exit status.
     Note that when called in a subshell, return will only exit that subshell
     and will not cause the original shell to exit a running function (see the
     while...read loop FAQ).

     Functions defined with the function reserved word are treated differently
     in the following ways from functions defined with the () notation:

     •   The $0 parameter is set to the name of the function (Bourne-style
         functions leave $0 untouched).

     •   OPTIND is saved/reset and restored on entry and exit from the func-
         tion so getopts can be used properly both inside and outside the
         function (Bourne-style functions leave OPTIND untouched, so using
         getopts inside a function interferes with using getopts outside the

     •   Shell options (set -o) except -p (-o privileged) have local scope,
         i.e. changes inside a function are reset upon its exit.

     In the future, the following differences may also be added:

     •   A separate trap/signal environment will be used during the execution
         of functions. This will mean that traps set inside a function will
         not affect the shell's traps and signals that are not ignored in the
         shell (but may be trapped) will have their default effect in a func-

     •   The EXIT trap, if set in a function, will be executed after the func-
         tion returns.

Command execution

     After evaluation of command-line arguments, redirections and parameter
     assignments, the type of command is determined: a special built-in com-
     mand, a function, a normal builtin or the name of a file to execute found
     using the PATH parameter. The checks are made in the above order. Special
     built-in commands differ from other commands in that the PATH parameter
     is not used to find them, an error during their execution can cause a
     non-interactive shell to exit, and parameter assignments that are speci-
     fied before the command are kept after the command completes. Regular
     built-in commands are different only in that the PATH parameter is not
     used to find them.

     POSIX special built-in utilities:

     ., :, break, continue, eval, exec, exit, export, readonly, return, set,
     shift, times, trap, unset

     Additional mksh commands keeping assignments:

     source, typeset

     All other builtins are not special; these are at least:

     [, alias, bg, bind, builtin, cd, command, echo, false, fc, fg, getopts,
     jobs, kill, let, print, pwd, read, realpath, rename, suspend, test, true,
     ulimit, umask, unalias, wait, whence

     Once the type of command has been determined, any command-line parameter
     assignments are performed and exported for the duration of the command.

     The following describes the special and regular built-in commands and
     builtin-like reserved words, as well as some optional utilities:

     . file [arg ...]
            (keeps assignments, special) This is called the "dot" command. Ex-
            ecute the commands in file in the current environment. The file is
            searched for in the directories of PATH. If arguments are given,
            the positional parameters may be used to access them while file is
            being executed. If no arguments are given, the positional parame-
            ters are those of the environment the command is used in.

     : [...]
            (keeps assignments, special) The null command.
            Exit status is set to zero.

     Lb64decode [string]
            (dot.mkshrc function) Decode string or standard input to binary.

     Lb64encode [string]
            (dot.mkshrc function) Encode string or standard input as base64.

     Lbafh_add [string]
            (dot.mkshrc functions) Implement the Better Avalance for Jenkins
            Hash (IV=1). This is the same hash mksh currently uses internally.
            After calling Lbafh_init, call Lbafh_add multiple times until all
            input is read, then call Lbafh_finish, which writes the result to
            the unsigned integer Lbafh_v variable for your consumption.

     Lstripcom [file ...]
            (dot.mkshrc function) Same as cat(1) but strips any empty lines
            and comments (from any '#' character onwards, no escapes) and
            reduces any amount of whitespace to one space character.

     [ expression ]
            (regular) See test.

     alias [-d | -t [-r] | -+x] [-p] [+] [name[=value] ...]
            (regular) Without arguments, alias lists all aliases. For any name
            without a value, the existing alias is listed. Any name with a
            value defines an alias; see Aliases above. [][A-Za-z0-9_!%+,.@:-]
            are valid in names, except they may not begin with a plus or
            hyphen-minus, and [[ is not a valid alias name.

            When listing aliases, one of two formats is used. Normally,
            aliases are listed as name=value, where value is quoted as neces-
            sary. If options were preceded with '+', or a lone '+' is given on
            the command line, only name is printed.

            The -d option causes directory aliases which are used in tilde ex-
            pansion to be listed or set (see Tilde expansion above).

            With -p, each alias is listed with the string "alias " prefixed.

            The -t option indicates that tracked aliases are to be listed/set
            (values given with the command are ignored for tracked aliases).

            The -r option indicates that all tracked aliases are to be reset.

            The -x option sets (+x clears) the export attribute of an alias,
            or, if no names are given, lists the aliases with the export at-
            tribute (exporting an alias has no effect).

            (built-in alias) See Functions above.

     bg [job ...]
            (regular, needs job control) Resume the specified stopped job(s)
            in the background. If no jobs are specified, %+ is assumed. See
            Job control below for more information.

     bind -l
            (regular) The names of editing commands strings can be bound to
            are listed. See Emacs editing mode for more information.

     bind [string ...]
            The current bindings, for string, if given, else all, are listed.
            Note: Default prefix bindings (1=Esc, 2=^X, 3=NUL) assumed.

     bind string=[editing-command] [...]
     bind -m string=substitute [...]
            To string, which should consist of a control character optionally
            preceded by one of the three prefix characters and optionally suc-
            ceeded by a tilde character, the editing-command is bound so that
            future input of the string will immediately invoke that editing
            command. If a tilde postfix is given, a tilde trailing the control
            character is ignored. If -m (macro) is given, future input of the
            string will be replaced by the given NUL-terminated substitute
            string, wherein prefix/control/tilde characters mapped to editing
            commands (but not those mapped to other macros) will be processed.

            The entire argument may be written using extended caret notation:
            ^Z represents Ctrl-Z; ^+Z represents UTF-8 Meta-Ctrl-Z, and both
            ^!Z and \x9A represent ASCII Meta-Ctrl-Z. Otherwise, a backslash
            escapes the next character, removing the special meaning from
            backslashes, carets and (for the string part) equals signs. (These
            backslashes obviously must be quoted for the shell.) Note that,
            although only three prefix characters (usually Esc, ^X and NUL)
            are usable, some multi-character sequences can be supported.

     break [level]
            (keeps assignments, special) Exit the levelth inner-most for,
            select, until or while loop. level defaults to 1.

     builtin [--] command [arg ...]
            (regular) Execute the built-in command command.

     \builtin command [arg ...]
            (regular, decl-forwarder) Same as builtin. Additionally acts as
            declaration utility forwarder, i.e. this is a declaration utility
            (see Tilde expansion) iff command is a declaration utility.

     cd [-L] [dir]
     cd -P [-e] [dir]
     chdir [-eLP] [dir]
            (regular) Set the working directory to dir. If the parameter
            CDPATH is set, it lists the search path for the directory contain-
            ing dir. An unset or empty path means the current directory. If
            dir is found in any component of the CDPATH search path other than
            an unset or empty path, the name of the new working directory will
            be written to standard output. If dir is missing, the home direc-
            tory HOME is used. If dir is "-", the previous working directory
            is used (see the OLDPWD parameter).

            If the -L option (logical path) is used or if the physical option
            isn't set (see the set command below), references to ".." in dir
            are relative to the path used to get to the directory. If the -P
            option (physical path) is used or if the physical option is set,
            ".." is relative to the filesystem directory tree. The PWD and
            OLDPWD parameters are updated to reflect the current and old work-
            ing directory, respectively. If the -e option is set for physical
            filesystem traversal and PWD could not be set, the exit code is 1;
            greater than 1 if an error occurred, 0 otherwise.

     cd [-eLP] old new
     chdir [-eLP] old new
            (regular) The string new is substituted for old in the current
            directory, and the shell attempts to change to the new directory.

     cls    (dot.mkshrc alias) Reinitialise the display (hard reset).

     command [-pVv] cmd [arg ...]
            (regular, decl-forwarder) If neither the -v nor -V option is
            given, cmd is executed exactly as if command had not been speci-
            fied, with two exceptions: firstly, cmd cannot be a shell func-
            tion; and secondly, special built-in commands lose their special-
            ness (i.e. redirection and utility errors do not cause the shell
            to exit, and command assignments are not permanent).

            If the -p option is given, a default search path, whose actual
            value is system-dependent, is used instead of the current PATH.

            If the -v option is given, instead of executing cmd, information
            about what would be executed is given for each argument. For buil-
            tins, functions and keywords, their names are simply printed; for
            aliases, a command that defines them is printed; for utilities
            found by searching the PATH parameter, the full path of the com-
            mand is printed. If no command is found (i.e. the path search
            fails), nothing is printed and command exits with a non-zero
            status. The -V option is like the -v option, but more verbose.

     continue [level]
            (keeps assignments, special) Jumps to the beginning of the levelth
            inner-most for, select, until or while loop. level defaults to 1.

     dirs [-lnv]
            (dot.mkshrc function) Print the directory stack. -l causes tilde
            expansion to occur in the output. -n causes line wrapping before
            80 columns, whereas -v causes numbered vertical output.

     doch   (dot.mkshrc alias) Execute the last command with sudo(8).

     echo [-Een] [arg ...]
            (regular) Warning: this utility is not portable; use the standard
            Korn shell built-in utility print in new code instead.

            Print arguments, separated by spaces, followed by a newline, to
            standard output. The newline is suppressed if any of the arguments
            contain the backslash sequence "\c". See the print command below
            for a list of other backslash sequences that are recognised.

            The options are provided for compatibility with BSD shell scripts.
            The -E option suppresses backslash interpretation, -e enables it
            (normally default), -n suppresses the trailing newline, and any-
            thing else causes the word to be printed as argument instead.

            If the posix or sh option is set or this is a direct builtin call
            or print -R, only the first argument is treated as an option, and
            only if it is exactly "-n". Backslash interpretation is disabled.

     enable [-anps] [name ...]
            (dot.mkshrc function) Hide and unhide built-in utilities, aliases
            and functions and those defined in dot.mkshrc.

            If no name is given or the -p option is used, builtins are printed
            (behind the string "enable ", followed by "-n " if the builtin is
            currently disabled), otherwise, they are disabled (if -n is given)
            or re-enabled.

            When printing, only enabled builtins are printed by default; the
            -a options prints all builtins, while -n prints only disabled
            builtins instead; -s limits the list to POSIX special builtins.

     eval command ...
            (keeps assignments, special) The arguments are concatenated, with
            a space between each, to form a single string which the shell then
            parses and executes in the current execution environment.

     exec [-a argv0] [-c] [command [arg ...]]
            (keeps assignments, special) The command (with arguments) is exe-
            cuted without forking, fully replacing the shell process; this is
            absolute, i.e. exec never returns, even if the command is not
            found. The -a option permits setting a different argv[0] value,
            and -c clears the environment before executing the child process,
            except for the _ parameter and direct assignments.

            If no command is given except for I/O redirection, the I/O
            redirection is permanent and the shell is not replaced. Any file
            descriptors greater than 2 which are opened or dup(2)'d in this
            way are not made available to other executed commands (i.e. com-
            mands that are not built-in to the shell). Note that the Bourne
            shell differs here; it does pass these file descriptors on.

     exit [status]
            (keeps assignments, special) The shell or subshell exits with the
            specified errorlevel (or the current value of the $? parameter).

     export [-p] [parameter[=value]]
            (keeps assignments, special, decl-util) Sets the export attribute
            of the named parameters. Exported parameters are passed in the en-
            vironment to executed commands. If values are specified, the named
            parameters are also assigned. This is a declaration utility.

            If no parameters are specified, all parameters with the export at-
            tribute set are printed one per line: either their names, or, if a
            "-" with no option letter is specified, name=value pairs, or, with
            the -p option, export commands suitable for re-entry.

            (OS/2) Null command required for shebang-like functionality.

     false  (regular) A command that exits with a non-zero status.

     fc [-e editor | -l [-n]] [-r] [first [last]]
            (regular) first and last select commands from the history. Com-
            mands can be selected by history number (negative numbers go back-
            wards from the current, most recent, line) or a string specifying
            the most recent command starting with that string. The -l option
            lists the command on standard output, and -n inhibits the default
            command numbers. The -r option reverses the order of the list.
            Without -l, the selected commands are edited by the editor speci-
            fied with the -e option or, if no -e is specified, the editor
            specified by the FCEDIT parameter (if this parameter is not set,
            /bin/ed is used), and the result is executed by the shell.

     fc -e - | -s [-g] [old=new] [prefix]
            (regular) Re-execute the selected command (the previous command by
            default) after performing the optional substitution of old with
            new. If -g is specified, all occurrences of old are replaced with
            new. The meaning of -e - and -s is identical: re-execute the
            selected command without invoking an editor. This command is usu-
            ally accessed with the predefined: alias r='fc -e -'

     fg [job ...]
            (regular, needs job control) Resume the specified job(s) in the
            foreground. If no jobs are specified, %+ is assumed.
            See Job control below for more information.

     functions [name ...]
            (built-in alias) Display the function definition commands
            corresponding to the listed, or all defined, functions.

     getopts optstring name [arg ...]
            (regular) Used by shell procedures to parse the specified argu-
            ments (or positional parameters, if no arguments are given) and to
            check for legal options. Options that do not take arguments may be
            grouped in a single argument. If an option takes an argument and
            the option character is not the last character of the word it is
            found in, the remainder of the word is taken to be the option's
            argument; otherwise, the next word is the option's argument.

            optstring contains the option letters to be recognised. If a
            letter is followed by a colon, the option takes an argument.

            Each time getopts is invoked, it places the next option in the
            shell parameter name. If the option was introduced with a '+', the
            character placed in name is prefixed with a '+'. If the option
            takes an argument, it is placed in the shell parameter OPTARG.

            When an illegal option or a missing option argument is encoun-
            tered, a question mark or a colon is placed in name (indicating an
            illegal option or missing argument, respectively) and OPTARG is
            set to the option letter that caused the problem. Furthermore, un-
            less optstring begins with a colon, a question mark is placed in
            name, OPTARG is unset and a diagnostic is shown on standard error.

            getopts records the index of the argument to be processed by the
            next call in OPTIND. When the end of the options is encountered,
            getopts returns a non-zero exit status. Options end at the first
            argument that does not start with a '-' (non-option argument) or
            when a "--" argument is encountered.

            Option parsing can be reset by setting OPTIND to 1 (this is done
            automatically whenever the shell or a shell procedure is invoked).

            Warning: Changing the value of the shell parameter OPTIND to a
            value other than 1 or parsing different sets of arguments without
            resetting OPTIND may lead to unexpected results.

     hash [-r] [name ...]
            (built-in alias) Without arguments, any hashed executable command
            paths are listed. The -r option causes all hashed commands to be
            removed from the cache. Each name is searched as if it were a com-
            mand name and added to the cache if it is an executable command.

     hd [file ...]
            (dot.mkshrc alias or function) Hexdump stdin or arguments legibly.

     history [-nr] [first [last]]
            (built-in alias) Same as fc -l (see above).

     integer [flags] [name[=value] ...]
            (built-in alias) Same as typeset -i (see below).

     jobs [-lnp] [job ...]
            (regular) Display information about the specified job(s); if no
            jobs are specified, all jobs are displayed. The -n option causes
            information to be displayed only for jobs that have changed state
            since the last notification. If the -l option is used, the process
            ID of each process in a job is also listed. The -p option causes
            only the process group of each job to be printed. See Job control
            below for the format of job and the displayed job.

     kill [-s signame | -signum | -signame] { job | pid | pgrp } ...
            (regular) Send the specified signal to the specified jobs, process
            IDs or process groups. If no signal is specified, the TERM signal
            is sent. If a job is specified, the signal is sent to the job's
            process group. See Job control below for the format of job.

     kill -l [exit-status ...]
            (regular) Print the signal name corresponding to exit-status. If
            no arguments are specified, a list of all the signals with their
            numbers and a short description of each are printed.

     let [expression ...]
            (regular) Each expression is evaluated (see Arithmetic expressions
            above). If all expressions evaluate successfully, the exit status
            is 0 (1) if the last expression evaluated to non-zero (zero). If
            an error occurs during the parsing or evaluation of an expression,
            the exit status is greater than 1. Since expressions may need to
            be quoted, (( expr )) is syntactic sugar for:
                  { \\builtin let 'expr'; }

     local [flags] [name[=value] ...]
            (built-in alias) Same as typeset (see below).

     mknod [-m mode] name b|c major minor
     mknod [-m mode] name p
            (optional) Create a device special file. The file type may be one
            of b (block type device), c (character type device) or p (named
            pipe, FIFO). The file created may be modified according to its
            mode (via the -m option), major (major device number), and minor
            (minor device number). This is not normally part of mksh; however,
            distributors may have added this as builtin as a speed hack.

     nameref [flags] [name[=value] ...]
            (built-in alias) Same as typeset -n (see below).

     popd [-lnv] [+n]
            (dot.mkshrc function) Pops the directory stack and returns to the
            new top directory. The flags are as in dirs (see above). A numeric
            argument +n selects the entry in the stack to discard.

     print [-AcelNnprsu[n] | -R [-n]] [argument ...]
            (regular) Print the specified argument(s) on the standard output,
            separated by spaces, terminated with a newline. The escapes men-
            tioned in Backslash expansion above, as well as "\c", which is
            equivalent to using the -n option, are interpreted.

            The options are as follows:

            -A     Each argument is arithmetically evaluated; the character
                   corresponding to the resulting value is printed. Empty
                   arguments separate input words.

            -c     The output is printed columnised, top to bottom then left
                   to right, similar to how tab completion (control character
                   escaping excepted), the kill -l built-in utility, the
                   select statement and the rs(1) utility do.

            -e     Restore backslash expansion after a previous -r.

            -l     Change the output word separator to newline.

            -N     Change the output word and line separator to ASCII NUL.

            -n     Do not print the trailing line separator.

            -p     Print to the co-process (see Co-processes above).

            -r     Inhibit backslash expansion.

            -s     Print to the history file instead of standard output.

            -u[n]  Print to the file descriptor n (defaults to 1 if omitted)
                   instead of standard output.

            The -R option mostly emulates the BSD echo(1) command which does
            not expand backslashes and interprets its first argument as option
            only if it is exactly "-n" (to suppress the trailing newline).

     printf format [arguments ...]
            (optional, defer always) If compiled in, format and print the ar-
            guments, supporting the bare POSIX-mandated minimum. If an exter-
            nal utility of the same name is found, it is deferred to, unless
            run as direct builtin call or from the builtin utility.

     pushd [-lnv]
            (dot.mkshrc function) Rotate the top two elements of the directory
            stack. The options are the same as for dirs (see above), and pushd
            changes to the topmost directory stack entry after acting.

     pushd [-lnv] +n
            (dot.mkshrc function) Rotate the element number n to the top.

     pushd [-lnv] name
            (dot.mkshrc function) Push name on top of the stack.

     pwd [-LP]
            (regular) Print the present working directory. If no options are
            given, pwd behaves as if the -P option (print physical path) was
            used if the physical shell option is set, the -L option (print
            logical path) otherwise. The logical path is the path used to cd
            to the current directory; the physical path is determined from the
            filesystem (by following ".." directories to the root directory).

     r [-g] [old=new] [prefix]
            (built-in alias) Same as fc -e - (see above).

     read [-A | -a] [-d x] [-N z | -n z] [-p | -u[n]] [-t n] [-rs] [p ...]
            (regular) Reads a line of input, separates the input into fields
            using the IFS parameter (see Substitution above) or other speci-
            fied means, and assigns each field to the specified parameters p.
            If no parameters are specified, the REPLY parameter is used to
            store the result. If there are more parameters than fields, the
            extra parameters are set to the empty string or 0; if there are
            more fields than parameters, the last parameter is assigned the
            remaining fields (including the word separators).

            The options are as follows:

            -A     Store the result into the parameter p (or REPLY) as array
                   of words. Only no or one parameter is accepted.

            -a     Store the result, without applying IFS word splitting, into
                   the parameter p (or REPLY) as array of characters (wide
                   characters if the utf8-mode option is enacted, octets oth-
                   erwise); the codepoints are encoded as decimal numbers by
                   default. Only no or one parameter is accepted.

            -d x   Use the first byte of x, NUL if empty, instead of the ASCII
                   newline character to delimit input lines.

            -N z   Instead of reading till end-of-line, read exactly z bytes.
                   Upon EOF, a partial read is returned with exit status 1.
                   After timeout, a partial read is returned with an exit
                   status as if SIGALRM were caught.

            -n z   Instead of reading till end-of-line, read up to z bytes but
                   return as soon as any bytes are read, e.g. from a slow ter-
                   minal device, or if EOF or a timeout occurs.

            -p     Read from the currently active co-process (see Co-processes
                   above for details) instead of from a file descriptor.

            -u[n]  Read from the file descriptor number n (defaults to 0, i.e.
                   standard input).
                   The argument must immediately follow the option character.

            -t n   Interrupt reading after n seconds (specified as positive
                   decimal value with an optional fractional part). The exit
                   status of read is the same as if SIGALRM were caught if the
                   timeout occurred, but partial reads may still be returned.

            -r     Normally, read strips backslash-newline sequences and any
                   remaining backslashes from input. This option enables raw
                   mode, in which backslashes are retained and ignored.

            -s     The input line is saved to the history.

            If the input is a terminal, both the -N and -n options set it into
            raw mode; they read an entire file if -1 is passed as z argument.

            The first parameter may have a question mark and a string appended
            to it, in which case the string is used as a prompt (printed to
            standard error before any input is read) if the input is a tty(4)
            (e.g. read nfoo?'number of foos: ').

            If no input is read or a timeout occurred, read exits with a non-
            zero status.

     readonly [-p] [parameter[=value] ...]
            (keeps assignments, special, decl-util) Sets the read-only attri-
            bute of the named parameters. If values are given, parameters are
            assigned these before disallowing writes. Once a parameter is made
            read-only, it cannot be unset and its value cannot be changed.

            If no parameters are specified, the names of all parameters with
            the read-only attribute are printed one per line, unless the -p
            option is used, in which case readonly commands defining all read-
            only parameters, including their values, are printed.

     realpath [--] name
            (defer with flags) Resolves an absolute pathname corresponding to
            name. If the resolved pathname either exists or can be created im-
            mediately, realpath returns 0 and prints the resolved pathname,
            otherwise or if an error occurs, it issues a diagnostic and re-
            turns nonzero. If name ends with a slash ('/'), resolving to an
            extant non-directory is also treated as error.

     rename [--] from to
            (defer always, needs rename(2)) Renames the file from to to. Both
            pathnames must be on the same device. Intended for emergency si-
            tuations (where /bin/mv becomes unusable); thin syscall wrapper.

     return [status]
            (keeps assignments, special) Returns from a function or . script
            with errorlevel status. If no status is given, the exit status of
            the last executed command is used. If used outside of a function
            or . script, it has the same effect as exit. Note that mksh treats
            both profile and ENV files as . scripts, while the original Korn
            shell only treated profiles as . scripts.

     rot13  (dot.mkshrc alias) ROT13-encrypts/-decrypts stdin to stdout.

     set [-+abCefhkmnpsUuvXx] [-+o option] [-+A name] [--] [argument ...]
     set -- [argument ...]
     set -+o
            (keeps assignments, special) The set command can be used to show
            all shell parameters (like typeset -), set (-) or clear (+) shell
            options, set an array parameter or the positional parameters.

            Options can be changed using the -+o option syntax, where option
            is the long name of an option, or using the -+letter syntax, where
            letter is the option's single letter name (not all options have
            both names). The following table lists short and long names (if
            extant) along with a description of what each option does:

            -A name
                 Sets the elements of the array parameter name to argument ...

                 If -A is used, the array is reset (i.e. emptied) first; if +A
                 is used, the first N elements are set (where N is the number
                 of arguments); the rest are left untouched. If name ends with
                 a '+', the array is appended to instead.

                 An alternative syntax for the command set -A foo -- a b c;
                 set -A foo+ -- d e which is compatible to GNU bash and also
                 supported by AT&T UNIX ksh93 is: foo=(a b c); foo+=(d e)

            -a | -o allexport
                 Make all variables assigned to while enabled as exported.

            -b | -o notify
                 Print job notification messages asynchronously instead of
                 just before the prompt. Only used with job control (-m).

            -C | -o noclobber
                 Prevent > redirection from overwriting existing files; '>|'
                 must be used to force overwriting instead. Note: This is not
                 safe to use for creation of temporary files or lockfiles due
                 to a TOCTOU in a check allowing one to redirect output to
                 /dev/null or other device files even in noclobber mode.

            -c   Commands are read from an argument string. Can only be used
                 when the shell is invoked.

            -e | -o errexit
                 Exit (after executing the ERR trap) as soon as an error oc-
                 curs or a command fails (i.e. exits with a non-zero status).
                 This does not apply to commands whose exit status is expli-
                 citly tested by a shell construct such as !, if, until or
                 while statements. For &&, || and pipelines (but mind -o
                 pipefail), only the status of the last command is tested.

            -f | -o noglob
                 Do not expand file name patterns.

            -h | -o trackall
                 Create tracked aliases for all executed commands (see Aliases
                 above). Enabled by default for non-interactive shells.

            -i | -o interactive
                 The shell is an interactive shell. This option can only be
                 used when the shell is invoked. See above for details.

            -k | -o keyword
                 Parameter assignments are recognised anywhere in a command.

            -l | -o login
                 The shell is a login shell. This option can only be used when
                 the shell is invoked. See above for what this means.

            -m | -o monitor
                 Enable job control (default for interactive shells).

            -n | -o noexec
                 Do not execute any commands. Useful for checking the syntax
                 of scripts. Ignored if reading commands from a tty.

            -p | -o privileged
                 The shell is a privileged shell. It is set automatically if,
                 when the shell starts, the real UID or GID does not match the
                 effective UID (EUID) or GID (EGID), respectively. See above
                 for a description of what this means.

                 If the shell is privileged, setting this flag after startup
                 file processing let it go full setuid and/or setgid. Clearing
                 the flag makes the shell drop privileges. Changing this flag
                 resets the supplementary groups vector.

            -r | -o restricted
                 The shell is a restricted shell. This option can only be used
                 when the shell is invoked. See above for what this means.

            -s | -o stdin
                 If used when the shell is invoked, commands are read from
                 standard input. Set automatically if the shell is invoked
                 with no arguments.

                 When -s is used with the set command it causes the specified
                 arguments to be sorted ASCIIbetically before assigning them
                 to the positional parameters (or to array name, with -A).

            -U | -o utf8-mode
                 Enable UTF-8 support in the Emacs editing mode and internal
                 string handling functions. This flag is disabled by default,
                 but can be enabled by setting it on the shell command line;
                 is enabled automatically for interactive shells if the POSIX
                 locale uses the UTF-8 codeset or, lacking POSIX locales, the
                 LC_ALL, LC_CTYPE or LANG environment variables either case-
                 insensitively equal "UTF-8" or "utf8" or have that as codeset

                 In near future, locale tracking will be implemented, which
                 means that set -+U is changed whenever one of the POSIX
                 locale-related environment variables changes.

            -u | -o nounset
                 Referencing of an unset parameter, other than "$@" or "$*",
                 is treated as an error, unless one of the '-', '+' or '='
                 modifiers is used.

            -v | -o verbose
                 Write shell input to standard error as it is read.

            -X | -o markdirs
                 Mark directories with a trailing '/' during globbing.

            -x | -o xtrace
                 Print commands when they are executed, preceded by PS4.

            -o asis
                 When quoting output, if not in EBCDIC mode and utf8-mode is
                 disabled, show C1 control characters "as is", that is, do not
                 escape them. Use with codepages where the range 0x80..0x9F
                 contains printable characters (such as 437, 850, 1252, etc.
                 but not the ISO 8859 series, for example).

            -o bgnice
                 Background jobs are run with lower priority.

            -o braceexpand
                 Enable brace expansion. This is enabled by default.

            -o emacs
                 Enable BRL emacs-like command-line editing (interactive
                 shells only); see Emacs editing mode. Enabled by default.

            -o gmacs
                 Enable gmacs-like command-line editing (interactive shells
                 only). Currently identical to emacs editing except that
                 transpose-chars (^T) acts slightly differently.

            -o ignoreeof
                 The shell will not (easily) exit when end-of-file is read;
                 exit must be used. To avoid infinite loops, the shell will
                 exit if EOF is read 13 times in a row.

            -o inherit-xtrace
                 Do not reset -o xtrace upon entering functions (default).

            -o nohup
                 Do not kill running jobs with a SIGHUP signal when a login
                 shell exits. Currently enabled by default.

            -o nolog
                 No effect. In the original Korn shell, this prevented func-
                 tion definitions from being stored in the history file.

            -o physical
                 Causes the cd and pwd commands to use "physical" (i.e. the
                 filesystem's) ".." directories instead of "logical" direc-
                 tories (i.e. the shell handles "..", which allows the user to
                 be oblivious of symbolic links to directories). Clear by de-
                 fault. Note that setting this option does not affect the
                 current value of the PWD parameter; only the cd command
                 changes PWD. See cd and pwd above for more details.

            -o pipefail
                 Make the exit status of a pipeline the rightmost non-zero er-
                 rorlevel, or zero if all commands exited with zero.

            -o posix
                 Behave closer to the standards (see POSIX mode for details).
                 Automatically enabled if the shell invocation basename, after
                 '-' and 'r' processing, begins with "sh" and (often used for
                 the lksh binary) this autodetection feature is compiled in.
                 As a side effect, setting this flag turns off the braceexpand
                 flag, which can be turned back on manually, and (unless both
                 are set in the same command) sh mode.

            -o sh
                 Enable kludge /bin/sh compatibility mode (see SH mode below
                 for details). Automatically enabled if the basename of the
                 shell invocation, after '-' and 'r' processing, begins with
                 "sh" and this autodetection feature is compiled in (rather
                 uncommon). As a side effect, setting this flag turns off the
                 braceexpand flag, which can be turned back on manually, and
                 posix mode (unless both are set in the same command).

            -o vi
                 Enable vi(1)-like command-line editing (interactive shells
                 only). See Vi editing mode for documentation and limitations.

            -o vi-esccomplete
                 In vi command-line editing, do command and file name comple-
                 tion when Esc (^[) is entered in command mode.

            -o vi-tabcomplete
                 In vi command-line editing, do command and file name comple-
                 tion when Tab (^I) is entered in insert mode (default).

            -o viraw
                 No effect. In the original Korn shell, unless viraw was set,
                 the vi command-line mode would let the tty(4) driver do the
                 work until Esc was entered. mksh is always in viraw mode.

            These options can also be used upon invocation of the shell. The
            current set of options with single letter names can be found in
            the parameter "$-". set -o with no option name will list all the
            options and whether each is on or off; set +o prints a command to
            restore the current option set, using the internal set -o .reset
            construct, which is an implementation detail; these commands are
            transient (only valid within the current shell session).

            A lone "-" clears both the -v and -x options (obsolete); it (or a
            lone "+") terminates option processing and is otherwise ignored.

            Remaining arguments, if any, are assigned (in order, unless -s is
            given) to name (with -A) or the positional parameters (i.e., $1,
            $2, etc). Use -- if the first argument begins with plus or dash.
            If options end with "--" and there are no remaining arguments, all
            positional parameters are cleared. If no options or arguments are
            given, the values of all parameters are printed (suitably quoted).

     setenv [name [value]]
            (dot.mkshrc function) Without arguments, display the names and
            values of all exported parameters. Otherwise, set name's export
            attribute, and its value to value (empty string if none given).

     shift [number]
            (keeps assignments, special) The positional parameters number+1,
            number+2, etc. (number defaults to 1) are renamed to 1, 2, etc.

     smores [file ...]
            (dot.mkshrc function) Simple pager: <Enter> next; 'q'+<Enter> quit

     source file [arg ...]
            (keeps assignments) Like . ("dot"), except that the current work-
            ing directory is appended to the search path. (GNU bash extension)

            (needs job control and getsid(2)) Stops the shell as if it had re-
            ceived the suspend character from the terminal.

            It is not possible to suspend a login shell unless the parent pro-
            cess is a member of the same terminal session but is a member of a
            different process group. As a general rule, if the shell was
            started by another shell or via su(1), it can be suspended.

     test expression
     [ expression ]
            (regular) test evaluates the expression and exits with status code
            0 if true, 1 if false, or greater than 1 if there was an error. It
            is often used as the condition command of if and while statements.
            All file expressions, except -h and -L, follow symbolic links.

            The following basic expressions are available:

            -a file
                 file exists.

            -b file
                 file is a block special device.

            -c file
                 file is a character special device.

            -d file
                 file is a directory.

            -e file
                 file exists.

            -f file
                 file is a regular file.

            -G file
                 file's group is the shell's effective group ID.

            -g file
                 file's mode has the setgid bit set.

            -H file
                 file is a context dependent directory (only useful on HP-UX).

            -h file
                 file is a symbolic link.

            -k file
                 file's mode has the sticky(7) bit set.

            -L file
                 file is a symbolic link.

            -O file
                 file's owner is the shell's effective user ID.

            -p file
                 file is a named pipe (FIFO).

            -r file
                 file exists and is readable.

            -S file
                 file is a unix(4)-domain socket.

            -s file
                 file is not empty.

            -t fd
                 File descriptor fd is a tty(4) device.

            -u file
                 file's mode has the setuid bit set.

            -w file
                 file exists and is writable.

            -x file
                 file exists and is executable.

            file1 -nt file2
                 file1 is newer than file2 or file1 exists and file2 does not.

            file1 -ot file2
                 file1 is older than file2 or file2 exists and file1 does not.

            file1 -ef file2
                 file1 is the same file as file2.

                 string has non-zero length.

            -n string
                 string is not empty.

            -z string
                 string is empty.

            -v name
                 The shell parameter name is set.

            -o option
                 Shell option is set (see the set command above for a list of
                 options). As a non-standard extension, if the option starts
                 with a '!', the test is negated; the test always fails if
                 option doesn't exist (so [ -o foo -o -o !foo ] returns true
                 if and only if option foo exists). The same can be achieved
                 with [ -o ?foo ] like in AT&T UNIX ksh93. option can also be
                 the short flag prefixed with either '-' or '+' (no logical
                 negation), for example "-x" or "+x" instead of "xtrace".

            string = string
                 Strings are equal. In double brackets, pattern matching (R59+
                 using extglobs) occurs if the right-hand string isn't quoted.

            string == string
                 Same as '=' (deprecated).

            string != string
                 Strings are not equal. See '=' regarding pattern matching.

            string > string
                 First string operand is greater than second string operand.

            string < string
                 First string operand is less than second string operand.

            number -eq number
                 Numbers compare equal.

            number -ne number
                 Numbers compare not equal.

            number -ge number
                 Numbers compare greater than or equal.

            number -gt number
                 Numbers compare greater than.

            number -le number
                 Numbers compare less than or equal.

            number -lt number
                 Numbers compare less than.

            The above basic expressions, in which unary operators have pre-
            cedence over binary operators, may be combined with the following
            operators (listed in increasing order of precedence):

                  expr -o expr            Logical OR.
                  expr -a expr            Logical AND.
                  ! expr                  Logical NOT.
                  ( expr )                Grouping.

            Note that a number actually may be an arithmetic expression, such
            as a mathematical term or the name of an integer variable:

                  x=1; [ "x" -eq 1 ]      evaluates to true

            Note that some special rules are applied (courtesy of POSIX) if
            the number of arguments to test or inside the brackets [ ... ] is
            less than five: if leading "!" arguments can be stripped such that
            only one to three arguments remain, then the lowered comparison is
            executed; (thanks to XSI) parentheses \( ... \) lower four- and
            three-argument forms to two- and one-argument forms, respectively;
            three-argument forms ultimately prefer binary operations, followed
            by negation and parenthesis lowering; two- and four-argument forms
            prefer negation followed by parenthesis; the one-argument form al-
            ways implies -n. To assume this is not necessarily portable.

            Note: A common mistake is to use "if [ $foo = bar ]" which fails
            if parameter "foo" is empty or unset, if it has embedded spaces
            (i.e. IFS octets) or if it is a unary operator like "!" or "-n".
            Use tests like "if [ x"$foo" = x"bar" ]" instead, or the double-
            bracket construct (see [[ above): "if [[ $foo = bar ]]" or, to
            avoid pattern matching, "if [[ $foo = "$bar" ]]"; the [[ ... ]]
            construct is not only more secure to use but also often faster.
            Similarily, operators need to be quoted as usual for test / [.

     time [-p] [pipeline]
            (reserved word) If a pipeline is given, the times used to execute
            the pipeline are reported. If no pipeline is given, then the user
            and system time used by the shell itself, and all the commands it
            has run since it was started, are reported.

            The times reported are the real time (elapsed time from start to
            finish), the user CPU time (time spent running in user mode), and
            the system CPU time (time spent running in kernel mode).

            Times are reported to standard error; the format of the output is:

                  0m0.03s real     0m0.02s user     0m0.01s system

            If the -p option is given (which is only permitted if pipeline is
            a simple command), the output is slightly longer:

                  real     0.03
                  user     0.02
                  sys      0.01

            Simple redirections of standard error do not affect time's output:

                  $ time sleep 1 2>afile
                  $ { time sleep 1; } 2>afile

            Times for the first command do not go to "afile", but those of the
            second command do.

     times  (keeps assignments, special) Print the accumulated user and system
            times (see above) used both by the shell and by processes that the
            shell started which have exited. The format of the output is:

                  0m0.01s 0m0.00s
                  0m0.04s 0m0.02s

     trap n [signal ...]
            (keeps assignments, special) If the first operand is a decimal un-
            signed integer, this resets all specified signals to the default
            action, i.e. is the same as calling trap with a dash ("-") as
            handler, followed by the arguments (interpreted as signals).

     trap [handler signal ...]
            (keeps assignments, special) Sets a trap handler that is to be ex-
            ecuted when any of the specified signals are received. handler is
            either an empty string, indicating the signals are to be ignored,
            a dash ("-"), indicating that the default action is to be taken
            for the signals (see signal(3)), or a string comprised of shell
            commands to be executed at the first opportunity (i.e. when the
            current command completes or before printing the next PS1 prompt)
            after receipt of one of the signals. signal is the name, possibly
            prefixed with "SIG", of a signal (e.g. PIPE, ALRM or SIGINT) or
            the number of the signal (see the kill -l command above).

            There are two special signals: EXIT (also known as 0), which is
            executed when the shell is about to exit, and ERR, which is exe-
            cuted after an error occurs; an error is something that would
            cause the shell to exit if the set -e or set -o errexit option
            were set. EXIT handlers are executed in the environment of the
            last executed command. The original Korn shell's DEBUG trap and
            handling of ERR and EXIT in functions are not yet implemented.

            Note that, for non-interactive shells, the trap handler cannot be
            changed for signals that were ignored when the shell started.

            With no arguments, the current state of the traps that have been
            set since the shell started is shown as a series of trap commands.
            Note that the output of trap cannot be usefully captured or piped
            to another process (an artifact of the fact that traps are cleared
            when subprocesses are created).

     true   (regular) A command that exits with a zero status.

     type name ...
            (built-in alias) Reveal how name would be interpreted as command.

     typeset [-+aglpnrtUux] [-L[n] | -R[n] | -Z[n]] [-i[n]] [name[=value] ...]
     typeset -f [-tux] [name ...]
            (keeps assignments, decl-util) Display or set attributes of shell
            parameters or functions. With no name arguments, parameter attri-
            butes are shown; if no options are used, the current attributes of
            all parameters are printed as typeset commands; if an option is
            given (or "-" with no option letter), all parameters and their
            values with the specified attributes are printed; if options are
            introduced with '+' (or "+" alone), only names are printed.

            If any name arguments are given, the attributes of the so named
            parameters are set (-) or cleared (+); inside a function, this
            will cause the parameters to be created (and set to "" if no value
            is given) in the local scope (except if -g is used). Values for
            parameters may optionally be specified. For name[*], the change
            affects all elements of the array, and no value may be specified.

            When -f is used, typeset operates on the attributes of functions.
            As with parameters, if no name arguments are given, functions are
            listed with their values (i.e. definitions) unless options are in-
            troduced with '+', in which case only the names are displayed.

            -a      Indexed array attribute.

            -f      Function mode. Display or set shell functions and their
                    attributes, instead of shell parameters.

            -g      "global" mode. Do not cause named parameters to be created
                    in the local scope when called inside a function.

            -i[n]   Integer attribute. n specifies the base to use when strin-
                    gifying the integer (if not specified, the base given in
                    the first assignment is used). Parameters with this attri-
                    bute may be assigned arithmetic expressions for values.

            -L[n]   Left justify attribute. n specifies the field width. If n
                    is not specified, the current width of the parameter (or
                    the width of its first assigned value) is used. Leading
                    whitespace (and digit zeros, if used with the -Z option)
                    is stripped. If necessary, values are either truncated or
                    padded with space to fit the field width.

            -l      Lower case attribute. All upper case ASCII characters in
                    values are converted to lower case. (In the original Korn
                    shell, this parameter meant "long integer" when used with
                    the -i option.)

            -n      Create a bound variable (name reference): any access to
                    the variable name will access the variable value in the
                    current scope (this is different from AT&T UNIX ksh93!)
                    instead. Also different from AT&T UNIX ksh93 is that value
                    is lazily evaluated at the time name is accessed. This can
                    be used by functions to access variables whose names are
                    passed as parameters, instead of resorting to eval.

            -p      Print complete typeset commands that can be used to re-
                    create the attributes and values of parameters.

            -R[n]   Right justify attribute. n specifies the field width. If n
                    is not specified, the current width of the parameter (or
                    the width of its first assigned value) is used. Trailing
                    whitespace is stripped. If necessary, values are either
                    stripped of leading characters or padded with space to fit
                    the field width.

            -r      Read-only attribute. Parameters with this attribute may
                    not be assigned to or unset. Once this attribute is set,
                    it cannot be turned off.

            -t      Tag attribute. This attribute has no meaning to the shell
                    for parameters and is provided for application use.

                    For functions, -t is the trace attribute. When functions
                    with the trace attribute are executed, the -o xtrace (-x)
                    shell option is temporarily turned on.

            -U      Unsigned integer attribute. Integers are printed as un-
                    signed values (combined with the -i option).

            -u      Upper case attribute. All lower case ASCII characters in
                    values are converted to upper case. (In the original Korn
                    shell, this parameter meant "unsigned integer" when used
                    with the -i option which meant upper case letters would
                    never be used for bases greater than 10. See -U above.)

                    For functions, -u is the undefined attribute, used with
                    FPATH. See Functions above for the implications of this.

            -x      Export attribute. Parameters are placed in the environment
                    of any executed commands. Functions cannot be exported for
                    security reasons ("shellshock").

            -Z[n]   Zero fill attribute. If not combined with -L, this is the
                    same as -R, except zero padding is used instead of space
                    padding. For integers, the number is padded, not the base.

            If any of the -i, -L, -l, -R, -U, -u or -Z options are changed,
            all others from this set are cleared, unless they are also given
            on the same command line.

     ulimit [-aBCcdefHilMmnOPpqrSsTtVvwx] [value]
            (regular) Display or set process limits. If no options are used,
            the file size limit (-f) is assumed. value, if specified, may be
            either an arithmetic expression or the word "unlimited". The lim-
            its affect the shell and any processes created by the shell after
            a limit is imposed. Note that systems may not allow some limits to
            be increased once they are set. Also note that the types of limits
            available are system dependent - some systems have only the -f
            limit, or not even that, or can set only the soft limits, etc.

            -a     Display all limits (soft limits unless -H is used).

            -B n   Set the socket buffer size to n kibibytes.

            -C n   Set the number of cached threads to n.

            -c n   Impose a size limit of n blocks on the size of core dumps.
                   Silently ignored if the system does not support this limit.

            -d n   Limit the size of the data area to n kibibytes.
                   On some systems, read-only maximum brk(2) size minus etext.

            -e n   Set the maximum niceness to n.

            -f n   Impose a size limit of n blocks on files written by the
                   shell and its child processes (any size may be read).

            -H     Set the hard limit only (the default is to set both hard
                   and soft limits). With -a, display all hard limits.

            -i n   Set the number of pending signals to n.

            -l n   Impose a limit of n kibibytes on the amount of locked
                   (wired) physical memory.

            -M n   Set the AIO locked memory to n kibibytes.

            -m n   Impose a limit of n kibibytes on the amount of physical
                   memory used.

            -n n   Impose a limit of n file descriptors that can be open at
                   once. On some systems attempts to set are silently ignored.

            -O n   Set the number of AIO operations to n.

            -P n   Limit the number of threads per process to n.

                   This option mostly matches AT&T UNIX ksh93's -T;
                   on AIX, see -r as used by its ksh though.

            -p n   Impose a limit of n processes that can be run by the user
                   (uid) at any one time.

            -q n   Limit the size of POSIX message queues to n bytes.

            -R n   (Linux) Limit the CPU time slice a real-time process can
                   use before performing a blocking syscall to n milliseconds.

            -r n   (AIX) Limit the number of threads per process to n.
                   (Linux) Set the maximum real-time priority to n.

            -S     Set the soft limit only (the default is to set both hard
                   and soft limits). With -a, display soft limits (default).

            -s n   Limit the size of the stack area to n kibibytes.

            -T n   Impose a time limit of n real seconds ("humantime") to be
                   used by each process.

            -t n   Impose a time limit of n CPU seconds spent in user mode to
                   be used by each process.

            -V n   Set the number of vnode monitors on Haiku to n.

            -v n   Impose a limit of n kibibytes on the amount of virtual
                   memory (address space) used.

            -w n   Limit the amount of swap space used to at most n kibibytes.

            -x n   Set the maximum number of file locks to n.

            As far as ulimit is concerned, a block is 512 bytes.

     umask [-S] [mask]
            (regular) Display or set the file permission creation mask or
            umask (see umask(2)). If the -S option is used, the mask displayed
            or set is symbolic; otherwise, it is an octal number.

            Symbolic masks are like those used by chmod(1). When used, they
            describe what permissions may be made available (as opposed to oc-
            tal masks in which a set bit means the corresponding bit is to be
            cleared). For example, "ug=rwx,o=" sets the mask so files will not
            be readable, writable or executable by "others", and is equivalent
            (on most systems) to the octal mask "007".

     unalias [-adt] [name ...]
            (regular) The aliases for the given names are removed. If the -a
            option is used, all aliases are removed. If the -t or -d options
            are used, the indicated operations are carried out on tracked or
            directory aliases, respectively.

     unset [-fv] parameter ...
            (keeps assignments, special) Unset the named parameters (-v, the
            default) or functions (-f). With parameter[*], attributes are re-
            tained, only values are unset. The exit status is non-zero if any
            of the parameters are read-only, zero otherwise (not portable).

     wait [job ...]
            (regular) Wait for the specified job(s) to finish. The exit status
            of wait is that of the last specified job; if the last job is
            killed by a signal, the exit status is 128 + the signal number
            (see kill -l exit-status above); if the last specified job cannot
            be found (because it never existed or had already finished), the
            exit status is 127. See Job control below for the format of job.
            wait will return if a signal for which a trap has been set is re-
            ceived or if a SIGHUP, SIGINT or SIGQUIT signal is received.

            If no jobs are specified, wait waits for all currently running
            jobs (if any) to finish and exits with a zero status. If job moni-
            toring is enabled, the completion status of jobs is printed (this
            is not the case when jobs are explicitly specified).

     whence [-pv] [name ...]
            (regular) Without the -v option, it is the same as command -v, ex-
            cept aliases are printed as their definition only. With the -v op-
            tion, it is exactly identical to command -V. In either case, with
            the -p option the search is restricted to the (current) PATH.

     which [-a] [name ...]
            (dot.mkshrc function) Without -a, behaves like whence -p (does a
            PATH search for each name printing the resulting pathname if
            found); with -a, matches in all PATH components are printed, i.e.
            the search is not stopped after a match. If no name was matched,
            the exit status is 2; if every name was matched, it is zero, oth-
            erwise it is 1. No diagnostics are produced on failure to match.

Job control

     Job control refers to the shell's ability to monitor and control jobs
     which are processes or groups of processes created for commands or pipe-
     lines. At a minimum, the shell keeps track of the status of the back-
     ground (i.e. asynchronous) jobs that currently exist; this information
     can be displayed using the jobs commands. If job control is fully enabled
     (using set -m or set -o monitor), as it is for interactive shells, the
     processes of a job are placed in their own process group. Foreground jobs
     can be stopped by typing the suspend character from the terminal (normal-
     ly ^Z); jobs can be restarted in either the foreground or background us-
     ing the commands fg and bg.

     Note that only commands that create processes (e.g. asynchronous com-
     mands, subshell commands and non-built-in, non-function commands) can be
     stopped; commands like read cannot be.

     When a job is created, it is assigned a job number. For interactive
     shells, this number is printed inside "[...]", followed by the process
     IDs of the processes in the job when an asynchronous command is run. A
     job may be referred to in the bg, fg, jobs, kill and wait commands either
     by the process ID of the last process in the command pipeline (as stored
     in the $! parameter) or by prefixing the job number with a percent sign
     ('%'). Other percent sequences can also be used to refer to jobs:

     %+ | %% | %    The most recently stopped job or, if there are no stopped
                    jobs, the oldest running job.

     %-             The job that would be the %+ job if the latter did not ex-

     %n             The job with job number n.

     %?string       The job with its command containing the string string (an
                    error occurs if multiple jobs are matched).

     %string        The job with its command starting with the string string
                    (an error occurs if multiple jobs are matched).

     When a job changes state (e.g. a background job finishes or foreground
     job is stopped), the shell prints the following status information:

           [number] flag status command


     number   is the job number of the job;

     flag     is the '+' or '-' character if the job is the %+ or %- job,
              respectively, or space if it is neither;

     status   indicates the current state of the job and can be:

              Done [number]
                         The job exited. number is the exit status of the job
                         which is omitted if the status is zero.

              Running    The job has neither stopped nor exited (note that
                         running does not necessarily mean consuming CPU
                         time - the process could be blocked waiting for some

              Stopped [signal]
                         The job was stopped by the indicated signal (if no
                         signal is given, the job was stopped by SIGTSTP).

              signal-description ["core dumped"]
                         The job was killed by a signal (e.g. memory fault,
                         hangup); use kill -l for a list of signal descrip-
                         tions. The "core dumped" message indicates the pro-
                         cess created a core file.

     command  is the command that created the process. If there are multiple
              processes in the job, each process will have a line showing its
              command and possibly its status, if it is different from the
              status of the previous process.

     When an attempt is made to exit the shell while there are jobs in the
     stopped state, the shell warns the user that there are stopped jobs and
     does not exit. If another attempt is immediately made to exit the shell,
     the stopped jobs are sent a SIGHUP signal and the shell exits. Similarly,
     if the nohup option is not set and there are running jobs when an attempt
     is made to exit a login shell, the shell warns the user and does not
     exit. If another attempt is immediately made to exit the shell, the run-
     ning jobs are sent a SIGHUP signal and the shell exits.

Terminal state

     The state of the controlling terminal can be modified by a command exe-
     cuted in the foreground, whether or not job control is enabled, but the
     modified terminal state is only kept past the job's lifetime and used for
     later command invocations if the command exits successfully (i.e. with an
     exit status of 0). When such a job is momentarily stopped or restarted,
     the terminal state is saved and restored, respectively, but it will not
     be kept afterwards. In interactive mode, when line editing is enabled,
     the terminal state is saved before being reconfigured by the shell for
     the line editor, then restored before running a command.

POSIX mode

     Entering set -o posix mode will cause mksh to behave even more POSIX com-
     pliant in places where the defaults or opinions differ. Note that mksh
     will still operate with unsigned 32-bit arithmetic; use lksh if arithmet-
     ic on the host long data type, complete with ISO C Undefined Behaviour,
     is required; refer to the lksh(1) manual page for details. Most other
     historic, AT&T UNIX ksh-compatible or opinionated differences can be dis-
     abled by using this mode; these are:

     •   The incompatible GNU bash I/O redirection &>file is not supported.

     •   File descriptors created by I/O redirections are inherited by child

     •   Numbers with a leading digit zero are interpreted as octal.

     •   The echo builtin does not interpret backslashes and only supports the
         exact option -n.

     •   Alias expansion with a trailing space only reruns on command words.

     •   Tilde expansion follows POSIX instead of Korn shell rules.

     •   The exit status of fg is always 0.

     •   kill -l only lists signal names, all in one line.

     •   getopts does not accept options with a leading '+'.

     •   exec skips builtins, functions and other commands and uses a PATH
         search to determine the utility to execute.

SH mode

     Compatibility mode; intended for use with legacy scripts that cannot
     easily be fixed; the changes are as follows:

     •   The incompatible GNU bash I/O redirection &>file is not supported.

     •   File descriptors created by I/O redirections are inherited by child

     •   The echo builtin does not interpret backslashes and only supports the
         exact option -n, unless built with -DMKSH_MIDNIGHTBSD01ASH_COMPAT.

     •   The substitution operations ${x#pat}, ${x##pat}, ${x%pat}, and
         ${x%%pat} wrongly do not require a parenthesis to be escaped and do
         not parse extglobs.

     •   The getopt construct from lksh(1) passes through the errorlevel.

     •   sh -c eats a leading -- if built with -DMKSH_MIDNIGHTBSD01ASH_COMPAT.

Interactive input line editing

     The shell supports three modes of reading command lines from a tty(4) in
     an interactive session, controlled by the emacs, gmacs and vi options (at
     most one of these can be set at once). The default is emacs. Editing
     modes can be set explicitly using the set built-in. If none of these op-
     tions are enabled, the shell simply reads lines using the normal tty(4)
     driver. If the emacs or gmacs option is set, the shell allows emacs-like
     editing of the command; similarly, if the vi option is set, the shell al-
     lows vi-like editing of the command. These modes are described in detail
     in the following sections.

     In these editing modes, if a line is longer than the screen width (see
     the COLUMNS parameter), a '>', '+' or '<' character is displayed in the
     last column indicating that there are more characters after, before and
     after, or before the current position, respectively. The line is scrolled
     horizontally as necessary.

     Completed lines are pushed into the history, unless they begin with an
     IFS octet or IFS white space or are the same as the previous line.

Emacs editing mode

     When the emacs option is set, interactive input line editing is enabled.
     Warning: This mode is slightly different from the emacs mode in the ori-
     ginal Korn shell. In this mode, various editing commands (typically bound
     to one or more control characters) cause immediate actions without wait-
     ing for a newline. Several editing commands are bound to particular con-
     trol characters when the shell is invoked; these bindings can be changed
     using the bind command.

     The following is a list of available editing commands. Each description
     starts with the name of the command, suffixed with a colon; a [n] (if the
     command can be prefixed with a count); and any keys the command is bound
     to by default, written using caret notation (e.g. the ASCII Esc character
     is written as ^[) or terminal-specific indications. A count prefix for a
     command is entered using the sequence ^[n, where n is one or more digits.
     Unless otherwise specified, if a count is omitted, it defaults to 1.

     Bigwords, as used below, are separated by spaces or tabs; words consist
     of alphanumerics, underscore ('_') or dollar sign ('$') characters.

     Note that editing command names are used only with the bind command.
     Furthermore, many editing commands are useful only on terminals with a
     visible cursor. The user's tty(4) characters (e.g. ERASE) are bound to
     reasonable substitutes and override the default bindings; their customary
     values are shown in parentheses below. The default bindings were chosen
     to resemble corresponding Emacs key bindings:

     abort: INTR (^C), ^G
             Abort the current command, save it to the history, empty the line
             buffer and set the exit state to interrupted.

     auto-insert: [n]
             (Most ordinary characters are bound to this command.) Simply
             causes the character to appear as literal input.

     backward-bigword: [n] ^[B
             Moves the cursor backward to the beginning of the bigword.

     backward-char: [n] ^B, ^XD, ANSI-CurLeft, PC-CurLeft
             Moves the cursor backward n characters.

     backward-word: [n] ^[b, ANSI-Ctrl-CurLeft, ANSI-Alt-CurLeft
             Moves the cursor backward to the beginning of the word.

     beginning-of-history: ^[<
             Moves to the beginning of the history.

     beginning-of-line: ^A, ANSI-Home, PC-Home
             Moves the cursor to the beginning of the edited input line.

     capitalise-bigword: [n] ^[C
             Uppercase the first character in the next n bigwords as below.

     capitalise-word: [n] ^[c
             Uppercase the first ASCII character in the next n words, leaving
             the cursor past the end of the last word.

     clear-screen: ^[^L
             Prints a compile-time configurable sequence to clear the screen
             and home the cursor, redraws the last line of the prompt string
             and the currently edited input line. The default sequence works
             for almost all standard terminals.

     comment: ^[#
             If the current line does not begin with a comment character, one
             is added at the beginning of the line and the line is entered (as
             if return had been pressed); otherwise, the existing comment
             characters are removed and the cursor is placed at the beginning
             of the line.

     complete: ^[^[
             Automatically completes as much as is unique of the command name
             or the file name containing the cursor. If the entire remaining
             command or file name is unique, a space is printed after its com-
             pletion, unless it is a directory name in which case '/' is ap-
             pended. If there is no command or file name with the current par-
             tial word as its prefix, a bell character is output (usually
             causing a beep to be sounded).

     complete-command: ^X^[
             Automatically completes as much as is unique of the command name
             having the partial word up to the cursor as its prefix, as in the
             complete command above.

     complete-file: ^[^X
             Automatically completes as much as is unique of the file name
             having the partial word up to the cursor as its prefix, as in the
             complete command described above.

     complete-list: ^I, ^[=
             Complete as much as is possible of the current word and list the
             possible completions for it. If only one completion is possible,
             match as in the complete command above. Note that ^I is usually
             generated by the Tab (tabulator) key.

     delete-bigword-backward: [n] ^[H
             Deletes n bigwords before the cursor.

     delete-bigword-forward: [n] ^[D
             Deletes characters after the cursor up to the end of n bigwords.

     delete-char-backward: [n] ERASE (^H), ^?, ^H
             Deletes n characters before the cursor.

     delete-char-forward: [n] ANSI-Del, PC-Del
             Deletes n characters after the cursor.

     delete-word-backward: [n] Pfx1+ERASE (^[^H), WERASE (^W), ^[^?, ^[^H, ^[h
             Deletes n words before the cursor.

     delete-word-forward: [n] ^[d
             Deletes characters after the cursor up to the end of n words.

     down-history: [n] ^N, ^XB, ANSI-CurDown, PC-CurDown
             Scrolls the history buffer forward n lines (later). Each input
             line originally starts just after the last entry in the history
             buffer, so down-history is not useful until either
             search-history, search-history-up or up-history has been per-

     downcase-bigword: [n] ^[L
             Lowercases the next n bigwords.

     downcase-word: [n] ^[l
             Lowercases the next n words.

     edit-line: [n] ^Xe
             Internally run the command fc -e "${VISUAL:-${EDITOR:-vi}}" -- n
             on a temporary script file to interactively edit line n (if n is
             not specified, the current line); then, unless the editor invoked
             exits nonzero but even if the script was not changed, execute the
             resulting script as if typed on the command line; both the edited
             (resulting) and original lines are added onto history.

     end-of-history: ^[>
             Moves to the end of the history.

     end-of-line: ^E, ANSI-End, PC-End
             Moves the cursor to the end of the input line.

     eot: ^_
             Acts as an end-of-file; this is useful because edit-mode input
             disables normal terminal input canonicalisation.

     eot-or-delete: [n] EOF (^D)
             If alone on a line, same as eot, otherwise, delete-char-forward.

     error: (not bound)
             Error (ring the bell).

     evaluate-region: ^[^E
             Evaluates the text between the mark and the cursor position (the
             entire line if no mark is set) as function substitution (if it
             cannot be parsed, the editing state is unchanged and the bell is
             rung to signal an error); $? is updated accordingly.

     exchange-point-and-mark: ^X^X
             Places the cursor where the mark is and sets the mark to where
             the cursor was.

     expand-file: ^[*
             Appends a '*' to the current word and replaces the word with the
             result of performing file globbing on the word. If no files match
             the pattern, the bell is rung.

     forward-bigword: [n] ^[F
             Moves the cursor forward to the end of the nth bigword.

     forward-char: [n] ^F, ^XC, ANSI-CurRight, PC-CurRight
             Moves the cursor forward n characters.

     forward-word: [n] ^[f, ANSI-Ctrl-CurRight, ANSI-Alt-CurRight
             Moves the cursor forward to the end of the nth word.

     goto-history: [n] ^[g
             Goes to history number n.

     kill-line: KILL (^U)
             Deletes the entire input line.

     kill-region: ^[^W
             Deletes the input between the cursor and the mark. Note: this
             used to be bound to ^W like in Emacs, which is usually taken by
             WERASE though, so it was moved.

     kill-to-eol: [n] ^K
             Deletes the input from the cursor to the end of the line if n is
             not specified; otherwise deletes characters between the cursor
             and column n.

     list: ^[?
             Prints a sorted, columnated list of command names or file names
             (if any) that can complete the partial word containing the cur-
             sor. Directory names have '/' appended to them.

     list-command: ^X?
             Prints a sorted, columnated list of command names (if any) that
             can complete the partial word containing the cursor.

     list-file: ^X^Y
             Prints a sorted, columnated list of file names (if any) that can
             complete the partial word containing the cursor. File type indi-
             cators are appended as described under list above.

     newline: ^J, ^M
             Causes the current input line to be processed by the shell. The
             current cursor position may be anywhere on the line.

     newline-and-next: ^O
             Causes the current input line to be processed by the shell, and
             the next line from history becomes the current line. This is only
             useful after an up-history, search-history or search-history-up.

     no-op: QUIT (^\)
             This does nothing.

     prefix-1: ^[
             Introduces a 2-character command sequence.

     prefix-2: ^X, ^[[, ^[O
             Introduces a multi-character command sequence.

     prefix-3: ^@
             Introduces a PC keyboard scancode.

     prev-hist-bigword: [n] ^[., ^[_
             If no count is given, the last bigword, otherwise the (n+1)th
             bigword of the previous line is inserted at the cursor, and the
             mark is set to the beginning of the inserted word. When invoked
             repeatedly, the inserted text is replaced by the corresponding
             bigword from the second-last, third-last, etc. line.

     quote: ^^, ^V
             The following character is taken literally rather than as an
             editing command.

     quote-region: ^[Q
             Escapes the text between the mark and the cursor position (the
             entire line if no mark is set) into a shell command argument.

     redraw: ^L
             Reprints the last line of the prompt string and the current input
             line on a new line.

     search-character-backward: [n] ^[^]
             Search backward in the current line for the nth occurrence of the
             next character typed.

     search-character-forward: [n] ^]
             Search forward in the current line for the nth occurrence of the
             next character typed.

     search-history: ^R
             Enter incremental search mode. The internal history list is
             searched backwards for commands matching the input. An initial
             '^' in the search string anchors the search at the beginning of
             the line. The escape key will leave search mode. Other commands,
             including sequences of escape as prefix-1 followed by a prefix-1
             or prefix-2 key, will be executed after leaving search mode. The
             abort (^G) command will restore the input line from before search
             started. Successive search-history commands continue searching
             backward to the following previous occurrence of the pattern. The
             history buffer retains only a finite number of lines; the oldest
             are discarded as necessary.

     search-history-down: ANSI-PgDn, PC-PgDn
             Search forwards (this command is only useful after an up-history,
             search-history-up or search-history) through the history buffer
             for commands whose beginning matches the portion of the input
             line before the cursor. When used on an empty line, this has the
             same effect as down-history.

     search-history-up: ANSI-PgUp, PC-PgUp
             Search backwards through the history buffer for commands whose
             beginning matches the portion of the input line before the cur-
             sor. When used on an empty line, this has the same effect as

     set-arg: ^[0 .. ^[9
             Mapped to begin prefixing a count to a command.

     set-mark-command: ^[<space>
             Set the mark at the cursor position.

     transpose-chars: ^T
             If at the end of line or, if the gmacs option is set, this ex-
             changes the two previous characters; otherwise, it exchanges the
             previous and current characters and moves the cursor one charac-
             ter to the right.

     up-history: [n] ^P, ^XA, ANSI-CurUp, PC-CurUp
             Scrolls the history buffer backward n lines (earlier).

     upcase-bigword: [n] ^[U
             Uppercase the next n bigwords.

     upcase-word: [n] ^[u
             Uppercase the next n words.

     version: ^[^V
             Display the version of mksh. The current edit buffer is restored
             as soon as a key is pressed. The restoring keypress is processed,
             unless it is a space.

     vt100-hack: ^[[1
             Mapped to internally represent some longer key sequences.

     yank: ^Y
             Inserts the most recently killed text string at the current cur-
             sor position.

     yank-pop: ^[y
             Immediately after a yank, replaces the inserted text string with
             the next previously killed text string.

     The tab completion escapes characters the same way as the following code:

     print -nr -- "${x@/[\"-\$\&-*:-?[\\\`\{-\~${IFS-$' \t\n'}]/\\$KSH_MATCH}"

Vi editing mode

     Note: The vi command-line editing mode has not yet been brought up to the
     same quality and feature set as the emacs mode. It is 8-bit clean but
     specifically does not support UTF-8 or MBCS.

     The vi command-line editor in mksh has basically the same commands as the
     vi(1) editor with the following exceptions:

     •   You start out in insert mode.

     •   There are file name and command completion commands: =, \, *, ^X, ^E,
         ^F and, optionally, <Tab> and <Esc>.

     •   The _ command is different (in mksh, it is the last argument command;
         in vi(1) it goes to the start of the current line).

     •   The / and G commands move in the opposite direction to the j command.

     •   Commands which don't make sense in a single line editor are not
         available (e.g. screen movement commands and ex(1)-style colon (:)

     Like vi(1), there are two modes: "insert" mode and "command" mode. In in-
     sert mode, most characters are simply put in the buffer at the current
     cursor position as they are typed; however, some characters are treated
     specially. In particular, the following characters are taken from current
     tty(4) settings (see stty(1)) and have their usual meaning (normal values
     are in parentheses): kill (^U), erase (^?), werase (^W), eof (^D), intr
     (^C) and quit (^\). In addition to the above, the following characters
     are also treated specially in insert mode:

     ^E       Command and file name enumeration (see below).

     ^F       Command and file name completion (see below). If used twice in a
              row, the list of possible completions is displayed; if used a
              third time, the completion is undone.

     ^H       Erases previous character.

     ^J | ^M  End of line. The current line is read, parsed and executed by
              the shell.

     ^V       Literal next. The next character typed is not treated specially
              (can be used to insert the characters being described here).

     ^X       Command and file name expansion (see below).

     <Esc>    Puts the editor in command mode (see below).

     <Tab>    Optional file name and command completion (see ^F above), en-
              abled with set -o vi-tabcomplete.

     In command mode, each character is interpreted as a command. Characters
     that don't correspond to commands, are illegal combinations of commands,
     or are commands that can't be carried out, all cause beeps. In the fol-
     lowing command descriptions, an [n] indicates the command may be prefixed
     by a number (e.g. 10l moves right 10 characters); if no number prefix is
     used, n is assumed to be 1 unless otherwise specified. The term "current
     position" refers to the position between the cursor and the character
     preceding the cursor. A "word" is a sequence of letters, digits and un-
     derscore characters or a sequence of non-letter, non-digit, non-
     underscore and non-whitespace characters (e.g. "ab2*&^" contains two
     words) and a "big-word" is a sequence of non-whitespace characters.

     Special mksh vi commands:

     The following commands are not in, or are different from, the normal vi
     file editor:

          Insert a space followed by the nth big-word from the last command in
          the history at the current position and enter insert mode; if n is
          not specified, the last word is inserted.

     #    Insert the comment character ('#') at the start of the current line
          and return the line to the shell (equivalent to I#^J).

          Like G, except if n is not specified, it goes to the most recent
          remembered line.

          Internally run the command fc -e "${VISUAL:-${EDITOR:-vi}}" -- n
          on a temporary script file to interactively edit line n (if n is not
          specified, the current line); then, unless the editor invoked exits
          nonzero but even if the script was not changed, execute the result-
          ing script as if typed on the command line; both the edited
          (resulting) and original lines are added onto history.

     * and ^X
          Command or file name expansion is applied to the current big-word
          (with an appended '*' if the word contains no file globbing
          characters) - the big-word is replaced with the resulting words. If
          the current big-word is the first on the line or follows one of the
          characters ';', '|', '&', '(' or ')' and does not contain a slash
          ('/'), then command expansion is done; otherwise file name expansion
          is done. Command expansion will match the big-word against all
          aliases, functions and built-in commands as well as any executable
          files found by searching the directories in the PATH parameter. File
          name expansion matches the big-word against the files in the current
          directory. After expansion, the cursor is placed just past the last
          word and the editor is in insert mode.

     [n]\, [n]^F, [n]<Tab>, and [n]<Esc>
          Command/file name completion. Replace the current big-word with the
          longest unique match obtained after performing command and file name
          expansion. <Tab> is only recognised if the vi-tabcomplete option is
          set, while <Esc> is only recognised if the vi-esccomplete option is
          set (see set -o). If n is specified, the nth possible completion is
          selected (as reported by the command/file name enumeration command).

     = and ^E
          Command/file name enumeration. List all the commands or files that
          match the current big-word.

     ^V   Display the version of mksh. The current edit buffer is restored as
          soon as a key is pressed. The restoring keypress is ignored.

     @c   Macro expansion. Execute the commands found in the alias _c.

     Intra-line movement commands:

     [n]h and [n]^H
             Move left n characters.

     [n]l and [n]<space>
             Move right n characters.

     0       Move to column 0.

     ^       Move to the first non-whitespace character.

     [n]|    Move to column n.

     $       Move to the last character.

     [n]b    Move back n words.

     [n]B    Move back n big-words.

     [n]e    Move forward to the end of the word, n times.

     [n]E    Move forward to the end of the big-word, n times.

     [n]w    Move forward n words.

     [n]W    Move forward n big-words.

     %       Find match. The editor looks forward for the nearest parenthesis,
             bracket or brace and then moves the cursor to the matching
             parenthesis, bracket or brace.

     [n]fc   Move forward to the nth occurrence of the character c.

     [n]Fc   Move backward to the nth occurrence of the character c.

     [n]tc   Move forward to just before the nth occurrence of the character

     [n]Tc   Move backward to just before the nth occurrence of the character

     [n];    Repeats the last f, F, t or T command.

     [n],    Repeats the last f, F, t or T command, but moves in the opposite

     Inter-line movement commands:

     [n]j, [n]+, and [n]^N
             Move to the nth next line in the history.

     [n]k, [n]-, and [n]^P
             Move to the nth previous line in the history.

     [n]G    Move to line n in the history; if n is not specified, the number
             of the first remembered line is used.

     [n]g    Like G, except if n is not specified, it goes to the most recent
             remembered line.

             Search backward through the history for the nth line containing
             string; if string starts with '^', the remainder of the string
             must appear at the start of the history line for it to match.

             Same as /, except it searches forward through the history.

     [n]n    Search for the nth occurrence of the last search string; the
             direction of the search is the same as the last search.

     [n]N    Search for the nth occurrence of the last search string; the
             direction of the search is the opposite of the last search.

     ANSI-CurUp, PC-PgUp
             Take the characters from the beginning of the line to the current
             cursor position as search string and do a history search, back-
             wards, for lines beginning with this string; keep the cursor po-
             sition. This works only in insert mode and keeps it enabled.

     ANSI-CurDown, PC-PgDn
             Take the characters from the beginning of the line to the current
             cursor position as search string and do a history search, for-
             wards, for lines beginning with this string; keep the cursor po-
             sition. This works only in insert mode and keeps it enabled.

     Edit commands

     [n]a    Append text n times; goes into insert mode just after the current
             position. The append is only replicated if command mode is re-
             entered i.e. <Esc> is used.

     [n]A    Same as a, except it appends at the end of the line.

     [n]i    Insert text n times; goes into insert mode at the current posi-
             tion. The insertion is only replicated if command mode is re-
             entered i.e. <Esc> is used.

     [n]I    Same as i, except the insertion is done just before the first
             non-blank character.

     [n]s    Substitute the next n characters (i.e. delete the characters and
             go into insert mode).

     S       Substitute whole line. All characters from the first non-blank
             character to the end of the line are deleted and insert mode is

             Change from the current position to the position resulting from n
             move-cmds (i.e. delete the indicated region and go into insert
             mode); if move-cmd is c, the line starting from the first non-
             blank character is changed.

     C       Change from the current position to the end of the line (i.e.
             delete to the end of the line and go into insert mode).

     [n]x    Delete the next n characters.

     [n]X    Delete the previous n characters.

     D       Delete to the end of the line.

             Delete from the current position to the position resulting from n
             move-cmds; move-cmd is a movement command (see above) or d, in
             which case the current line is deleted.

     [n]rc   Replace the next n characters with the character c.

     [n]R    Replace. Enter insert mode but overwrite existing characters in-
             stead of inserting before existing characters. The replacement is
             repeated n times.

     [n]~    Change the case of the next n characters.

             Yank from the current position to the position resulting from n
             move-cmds into the yank buffer; if move-cmd is y, the whole line
             is yanked.

     Y       Yank from the current position to the end of the line.

     [n]p    Paste the contents of the yank buffer just after the current po-
             sition, n times.

     [n]P    Same as p, except the buffer is pasted at the current position.

     Miscellaneous vi commands

     ^J and ^M
             The current line is read, parsed and executed by the shell.

     ^L and ^R
             Redraw the current line.

     [n].    Redo the last edit command n times.

     u       Undo the last edit command.

     U       Undo all changes that have been made to the current line.

     PC Home, End, Del and cursor keys
             They move as expected, both in insert and command mode.

     intr and quit
             The interrupt and quit terminal characters cause the current line
             to be removed to the history and a new prompt to be printed.


     ~/.mkshrc          User mkshrc profile (non-privileged interactive
                        shells); see Startup files. The location can be
                        changed at compile time (e.g. for embedded systems);
                        AOSP Android builds use /system/etc/mkshrc.
     ~/.profile         User profile (non-privileged login shells); see
                        Startup files near the top of this manual.
     /etc/profile       System profile (login shells); see Startup files.
     /etc/shells        Shell database.
     /etc/suid_profile  Privileged shells' profile (sugid); see Startup files.

     Note: On Android, /system/etc/ contains the system and suid profile.


     awk(1), cat(1), ed(1), getopt(1), lksh(1), sed(1), sh(1), stty(1),
     dup(2), execve(2), getgid(2), getuid(2), mknod(2), mkfifo(2), open(2),
     pipe(2), rename(2), wait(2), getopt(3), nl_langinfo(3), setlocale(3),
     signal(3), system(3), tty(4), shells(5), environ(7), script(7), utf-8(7),

     The FAQ at http://www.mirbsd.org/mksh-faq.htm or in the mksh.faq file.


     Morris Bolsky, The KornShell Command and Programming Language, Prentice
     Hall PTR, xvi + 356 pages, 1989, ISBN 978-0-13-516972-8 (0-13-516972-0).

     Morris I. Bolsky and David G. Korn, The New KornShell Command and
     Programming Language (2nd Edition), Prentice Hall PTR, xvi + 400 pages,
     1995, ISBN 978-0-13-182700-4 (0-13-182700-6).

     Stephen G. Kochan and Patrick H. Wood, UNIX Shell Programming, Sams, 3rd
     Edition, xiii + 437 pages, 2003, ISBN 978-0-672-32490-1 (0-672-32490-3).

     IEEE Inc., IEEE Standard for Information Technology - Portable Operating
     System Interface (POSIX), IEEE Press, Part 2: Shell and Utilities,
     xvii + 1195 pages, 1993, ISBN 978-1-55937-255-8 (1-55937-255-9).

     Bill Rosenblatt, Learning the Korn Shell, O'Reilly, 360 pages, 1993, ISBN
     978-1-56592-054-5 (1-56592-054-6).

     Bill Rosenblatt and Arnold Robbins, Learning the Korn Shell, Second
     Edition, O'Reilly, 432 pages, 2002, ISBN 978-0-596-00195-7

     Barry Rosenberg, KornShell Programming Tutorial, Addison-Wesley
     Professional, xxi + 324 pages, 1991, ISBN 978-0-201-56324-5


     The MirBSD Korn Shell is developed by mirabilos <m@mirbsd.org> as part of
     The MirOS Project. This shell is based on the public domain 7th edition
     Bourne shell clone by Charles Forsyth, who kindly agreed to, in countries
     where the Public Domain status of the work may not be valid, grant a
     copyright licence to the general public to deal in the work without res-
     triction and permission to sublicence derivatives under the terms of any
     (OSI approved) Open Source licence, and parts of the BRL shell by Doug A.
     Gwyn, Doug Kingston, Ron Natalie, Arnold Robbins, Lou Salkind and others.
     The first release of pdksh was created by Eric Gisin, and it was subse-
     quently maintained by John R. MacMillan, Simon J. Gerraty and Michael
     Rendell. The effort of several projects, such as Debian and OpenBSD, and
     other contributors including our users, to improve the shell is appreci-
     ated. See the documentation, website and source code (CVS) for details.

     mksh-os2 is developed by KO Myung-Hun <komh@chollian.net>.

     mksh-w32 is developed by Michael Langguth <lan@scalaris.com>.

     mksh/z/OS is contributed by Daniel Richard G. <skunk@iSKUNK.ORG>.

     The BSD daemon is Copyright (C) Marshall Kirk McKusick. The complete
     legalese is at: http://www.mirbsd.org/TaC-mksh.txt


     mksh provides a consistent, clear interface normally. This may deviate
     from POSIX in historic or opinionated places. set -o posix (see POSIX
     mode for details) will make the shell more conformant, but mind the FAQ
     (see SEE ALSO), especially regarding locales. mksh (but not lksh) pro-
     vides a consistent 32-bit integer arithmetic implementation, both signed
     and unsigned, with sign of the result of a remainder operation and wra-
     paround defined, even (defying POSIX) on 36-bit and 64-bit systems.

     mksh currently uses OPTU-16 internally, which is the same as UTF-8 and
     CESU-8 with 0000..FFFD being valid codepoints; raw octets map to
     U+EF80..U+EFFF for releases before R60, U-10000080..U-100000FF for R60
     onwards. Future compatibility note: there's work underway to use full 21-
     bit UTF-8 in mksh R60 or so.


     Suspending (using ^Z) pipelines like the one below will only suspend the
     currently running part of the pipeline; in this example, "fubar" is im-
     mediately printed on suspension (but not later after an fg).

           $ /bin/sleep 666 && echo fubar

     The truncation process involved when changing HISTFILE does not free old
     history entries (leaks memory) and leaks old entries into the new history
     if their line numbers are not overwritten by same-number entries from the
     persistent history file; truncating the on-disc file to HISTSIZE lines
     has always been broken and prone to history file corruption when multiple
     shells are accessing the file; the rollover process for the in-memory
     portion of the history is slow, should use memmove(3).

     This document attempts to describe mksh R59-CURRENT and up, compiled
     without any options impacting functionality, such as MKSH_SMALL, when not
     called as /bin/sh which, on some systems only, enables set -o posix or
     set -o sh automatically (whose behaviour differs across targets), for an
     operating environment supporting all of its advanced needs.

     Please report bugs in mksh to the public development mailing list at
     <miros-mksh@mirbsd.org> or, in the #!/bin/mksh channel, on IRC; for both,
     note the information at: http://www.mirbsd.org/mksh-faq.htm#contact

MirBSD                        December 13, 2022                             59

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