MirOS Manual: lksh(1)

LKSH(1)                      BSD Reference Manual                      LKSH(1)


     lksh - Legacy Korn shell built on mksh


     lksh [-+abCefhiklmnprUuvXx] [-+o opt] [-c string | -s | file [args ...]]


     lksh is a command interpreter intended exclusively for running legacy
     shell scripts. It is built on mksh; refer to its manual page for details
     on the scripting language. It is recommended to port scripts to mksh in-
     stead of relying on legacy or idiotic POSIX-mandated behaviour, since the
     MirBSD Korn Shell scripting language is much more consistent.

     Note that it's strongly recommended to invoke lksh with at least the -o
     posix option, if not both that and -o sh, to fully enjoy better compati-
     bility to the POSIX standard (which is probably why you use lksh over
     mksh in the first place) or legacy scripts, respectively.


     lksh currently has the following differences from mksh:

     •   There is no explicit support for interactive use, nor any command
         line editing or history code. Hence, lksh is not suitable as a user's
         login shell, either; use mksh instead.

     •   The KSH_VERSION string identifies lksh as "LEGACY KSH" instead of
         "MIRBSD KSH". Note that the rest of the version string is identical
         between the two shell flavours, and the behaviour and differences can
         change between versions; see the accompanying manual page mksh(1) for
         the versions this document applies to.

     •   lksh uses POSIX arithmetics, which has quite a few implications: The
         data type for arithmetics is the host ISO C long data type. Signed
         integer wraparound is Undefined Behaviour; this means that...

               $ echo $((2147483647 + 1))

         ... is permitted to, e.g. delete all files on your system (the figure
         differs for non-32-bit systems, the rule doesn't). The sign of the
         result of a modulo operation with at least one negative operand is
         unspecified. Shift operations on negative numbers are unspecified.
         Division of the largest negative number by -1 is Undefined Behaviour.
         The compiler is permitted to delete all data and crash the system if
         Undefined Behaviour occurs (see above for an example).

     •   lksh only offers the traditional ten file descriptors to scripts.

     •   The rotation arithmetic operators are not available.

     •   The shift arithmetic operators take all bits of the second operand
         into account; if they exceed permitted precision, the result is un-

     •   The GNU bash extension &> to redirect stdout and stderr in one go is
         not parsed.

     •   The mksh command line option -T is not available.

     •   Unless set -o posix is active, lksh always uses traditional mode for
         constructs like:

               $ set -- $(getopt ab:c "$@")
               $ echo $?

         POSIX mandates this to show 0, but traditional mode passes through
         the errorlevel from the getopt(1) command.

     •   Unlike AT&T UNIX ksh, mksh in -o posix or -o sh mode and lksh do not
         keep file descriptors > 2 private from sub-processes.

     •   Functions defined with the function reserved word share the shell op-
         tions (set -o) instead of locally scoping them.






     To use lksh as /bin/sh, compilation to enable set -o posix by default if
     called as sh is highly recommended for better standards compliance. For
     better compatibility with legacy scripts, such as many Debian maintainer
     scripts, Upstart and SYSV init scripts, and other unfixed scripts, using
     the compile-time options for enabling both set -o posix -o sh when the
     shell is run as sh is recommended.

     lksh tries to make a cross between a legacy bourne/posix compatibl-ish
     shell and a legacy pdksh-alike but "legacy" is not exactly specified.

     The set built-in command does not currently have all options one would
     expect from a full-blown mksh or pdksh.

     Talk to the MirOS development team using the mailing list at
     <miros-mksh@mirbsd.org> or the #!/bin/mksh (or #ksh) IRC channel at
     irc.freenode.net (Port 6697 SSL, 6667 unencrypted) if you need any furth-
     er quirks or assistance, and consider migrating your legacy scripts to
     work with mksh instead of requiring lksh.

MirOS                          October 9, 2015                               1

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