MirBSD manpage: perlrun(1)

PERLRUN(1)      Perl Programmers Reference Guide       PERLRUN(1)


     perlrun - how to execute the Perl interpreter


     perl [ -sTtuUWX ]      [ -hv ] [ -V[:configvar] ]
          [ -cw ] [ -d[t][:debugger] ] [ -D[number/list] ]
          [ -pna ] [ -Fpattern ] [ -l[octal] ] [ -0[octal/hexadecimal] ]
          [ -Idir ] [ -m[-]module ] [ -M[-]'module...' ] [ -f ]
          [ -C [number/list] ]      [ -P ]      [ -S ]
          [ -x[dir] ]      [ -i[extension] ]
          [ -e 'command' ] [ -- ] [ programfile ] [ argument ]...


     The normal way to run a Perl program is by making it
     directly executable, or else by passing the name of the
     source file as an argument on the command line.  (An
     interactive Perl environment is also possible--see perldebug
     for details on how to do that.) Upon startup, Perl looks for
     your program in one of the following places:

     1.  Specified line by line via -e switches on the command

     2.  Contained in the file specified by the first filename on
         the command line. (Note that systems supporting the #!
         notation invoke interpreters this way. See "Location of

     3.  Passed in implicitly via standard input.  This works
         only if there are no filename arguments--to pass argu-
         ments to a STDIN-read program you must explicitly
         specify a "-" for the program name.

     With methods 2 and 3, Perl starts parsing the input file
     from the beginning, unless you've specified a -x switch, in
     which case it scans for the first line starting with #! and
     containing the word "perl", and starts there instead.  This
     is useful for running a program embedded in a larger mes-
     sage.  (In this case you would indicate the end of the pro-
     gram using the "__END__" token.)

     The #! line is always examined for switches as the line is
     being parsed.  Thus, if you're on a machine that allows only
     one argument with the #! line, or worse, doesn't even recog-
     nize the #! line, you still can get consistent switch
     behavior regardless of how Perl was invoked, even if -x was
     used to find the beginning of the program.

     Because historically some operating systems silently chopped
     off kernel interpretation of the #! line after 32 charac-
     ters, some switches may be passed in on the command line,
     and some may not; you could even get a "-" without its

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     letter, if you're not careful. You probably want to make
     sure that all your switches fall either before or after that
     32-character boundary.  Most switches don't actually care if
     they're processed redundantly, but getting a "-" instead of
     a complete switch could cause Perl to try to execute stan-
     dard input instead of your program.  And a partial -I switch
     could also cause odd results.

     Some switches do care if they are processed twice, for
     instance combinations of -l and -0.  Either put all the
     switches after the 32-character boundary (if applicable), or
     replace the use of -0digits by "BEGIN{ $/ = "\0digits"; }".

     Parsing of the #! switches starts wherever "perl" is men-
     tioned in the line. The sequences "-*" and "- " are specifi-
     cally ignored so that you could, if you were so inclined,

         #!/bin/sh -- # -*- perl -*- -p
         eval 'exec perl -wS $0 ${1+"$@"}'
             if $running_under_some_shell;

     to let Perl see the -p switch.

     A similar trick involves the env program, if you have it.

         #!/usr/bin/env perl

     The examples above use a relative path to the perl inter-
     preter, getting whatever version is first in the user's
     path.  If you want a specific version of Perl, say,
     perl5.005_57, you should place that directly in the #!
     line's path.

     If the #! line does not contain the word "perl", the program
     named after the #! is executed instead of the Perl inter-
     preter.  This is slightly bizarre, but it helps people on
     machines that don't do #!, because they can tell a program
     that their SHELL is /usr/bin/perl, and Perl will then
     dispatch the program to the correct interpreter for them.

     After locating your program, Perl compiles the entire pro-
     gram to an internal form.  If there are any compilation
     errors, execution of the program is not attempted.  (This is
     unlike the typical shell script, which might run part-way
     through before finding a syntax error.)

     If the program is syntactically correct, it is executed.  If
     the program runs off the end without hitting an exit() or
     die() operator, an implicit exit(0) is provided to indicate
     successful completion.

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     #! and quoting on non-Unix systems

     Unix's #! technique can be simulated on other systems:


             extproc perl -S -your_switches

         as the first line in "*.cmd" file (-S due to a bug in
         cmd.exe's `extproc' handling).

         Create a batch file to run your program, and codify it
         in "ALTERNATE_SHEBANG" (see the dosish.h file in the
         source distribution for more information).

         The Win95/NT installation, when using the ActiveState
         installer for Perl, will modify the Registry to associ-
         ate the .pl extension with the perl interpreter.  If you
         install Perl by other means (including building from the
         sources), you may have to modify the Registry yourself.
         Note that this means you can no longer tell the differ-
         ence between an executable Perl program and a Perl
         library file.

         Under "Classic" MacOS, a perl program will have the
         appropriate Creator and Type, so that double-clicking
         them will invoke the MacPerl application. Under Mac OS
         X, clickable apps can be made from any "#!" script using
         Wil Sanchez' DropScript utility:
         http://www.wsanchez.net/software/ .

     VMS Put

             $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
             $ exit++ + ++$status != 0 and $exit = $status = undef;

         at the top of your program, where -mysw are any command
         line switches you want to pass to Perl.  You can now
         invoke the program directly, by saying "perl program",
         or as a DCL procedure, by saying @program (or implicitly
         via DCL$PATH by just using the name of the program).

         This incantation is a bit much to remember, but Perl
         will display it for you if you say "perl

     Command-interpreters on non-Unix systems have rather dif-
     ferent ideas on quoting than Unix shells.  You'll need to

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     learn the special characters in your command-interpreter
     ("*", "\" and """ are common) and how to protect whitespace
     and these characters to run one-liners (see -e below).

     On some systems, you may have to change single-quotes to
     double ones, which you must not do on Unix or Plan 9 sys-
     tems.  You might also have to change a single % to a %%.

     For example:

         # Unix
         perl -e 'print "Hello world\n"'

         # MS-DOS, etc.
         perl -e "print \"Hello world\n\""

         # Macintosh
         print "Hello world\n"
          (then Run "Myscript" or Shift-Command-R)

         # VMS
         perl -e "print ""Hello world\n"""

     The problem is that none of this is reliable: it depends on
     the command and it is entirely possible neither works.  If
     4DOS were the command shell, this would probably work

         perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""

     CMD.EXE in Windows NT slipped a lot of standard Unix func-
     tionality in when nobody was looking, but just try to find
     documentation for its quoting rules.

     Under the Macintosh, it depends which environment you are
     using.  The MacPerl shell, or MPW, is much like Unix shells
     in its support for several quoting variants, except that it
     makes free use of the Macintosh's non-ASCII characters as
     control characters.

     There is no general solution to all of this.  It's just a

     Location of Perl

     It may seem obvious to say, but Perl is useful only when
     users can easily find it.  When possible, it's good for both
     /usr/bin/perl and /usr/local/bin/perl to be symlinks to the
     actual binary.  If that can't be done, system administrators
     are strongly encouraged to put (symlinks to) perl and its
     accompanying utilities into a directory typically found
     along a user's PATH, or in some other obvious and convenient

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     In this documentation, "#!/usr/bin/perl" on the first line
     of the program will stand in for whatever method works on
     your system.  You are advised to use a specific path if you
     care about a specific version.


     or if you just want to be running at least version, place a
     statement like this at the top of your program:

         use 5.005_54;

     Command Switches

     As with all standard commands, a single-character switch may
     be clustered with the following switch, if any.

         #!/usr/bin/perl -spi.orig   # same as -s -p -i.orig

     Switches include:

          specifies the input record separator ($/) as an octal
          or hexadecimal number.  If there are no digits, the
          null character is the separator.  Other switches may
          precede or follow the digits.  For example, if you have
          a version of find which can print filenames terminated
          by the null character, you can say this:

              find . -name '*.orig' -print0 | perl -n0e unlink

          The special value 00 will cause Perl to slurp files in
          paragraph mode. The value 0777 will cause Perl to slurp
          files whole because there is no legal byte with that

          If you want to specify any Unicode character, use the
          hexadecimal format: "-0xHHH...", where the "H" are
          valid hexadecimal digits. (This means that you cannot
          use the "-x" with a directory name that consists of
          hexadecimal digits.)

     -a   turns on autosplit mode when used with a -n or -p.  An
          implicit split command to the @F array is done as the
          first thing inside the implicit while loop produced by
          the -n or -p.

              perl -ane 'print pop(@F), "\n";'

          is equivalent to

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              while (<>) {
                  @F = split(' ');
                  print pop(@F), "\n";

          An alternate delimiter may be specified using -F.

     -C [number/list]
          The "-C" flag controls some Unicode of the Perl Unicode

          As of 5.8.1, the "-C" can be followed either by a
          number or a list of option letters.  The letters, their
          numeric values, and effects are as follows; listing the
          letters is equal to summing the numbers.

              I     1    STDIN is assumed to be in UTF-8
              O     2    STDOUT will be in UTF-8
              E     4    STDERR will be in UTF-8
              S     7    I + O + E
              i     8    UTF-8 is the default PerlIO layer for input streams
              o    16    UTF-8 is the default PerlIO layer for output streams
              D    24    i + o
              A    32    the @ARGV elements are expected to be strings encoded in UTF-8
              L    64    normally the "IOEioA" are unconditional,
                         the L makes them conditional on the locale environment
                         variables (the LC_ALL, LC_TYPE, and LANG, in the order
                         of decreasing precedence) -- if the variables indicate
                         UTF-8, then the selected "IOEioA" are in effect

          For example, "-COE" and "-C6" will both turn on
          UTF-8-ness on both STDOUT and STDERR.  Repeating
          letters is just redundant, not cumulative nor toggling.

          The "io" options mean that any subsequent open() (or
          similar I/O operations) will have the ":utf8" PerlIO
          layer implicitly applied to them, in other words, UTF-8
          is expected from any input stream, and UTF-8 is pro-
          duced to any output stream.  This is just the default,
          with explicit layers in open() and with binmode() one
          can manipulate streams as usual.

          "-C" on its own (not followed by any number or option
          list), or the empty string "" for the "PERL_UNICODE"
          environment variable, has the same effect as "-CSDL".
          In other words, the standard I/O handles and the
          default "open()" layer are UTF-8-fied but only if the
          locale environment variables indicate a UTF-8 locale.
          This behaviour follows the implicit (and problematic)
          UTF-8 behaviour of Perl 5.8.0.

          You can use "-C0" (or "0" for "PERL_UNICODE") to

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          explicitly disable all the above Unicode features.

          The read-only magic variable "${^UNICODE}" reflects the
          numeric value of this setting.  This is variable is set
          during Perl startup and is thereafter read-only.  If
          you want runtime effects, use the three-arg open() (see
          "open" in perlfunc), the two-arg binmode() (see "bin-
          mode" in perlfunc), and the "open" pragma (see open).

          (In Perls earlier than 5.8.1 the "-C" switch was a
          Win32-only switch that enabled the use of Unicode-aware
          "wide system call" Win32 APIs. This feature was practi-
          cally unused, however, and the command line switch was
          therefore "recycled".)

     -c   causes Perl to check the syntax of the program and then
          exit without executing it.  Actually, it will execute
          "BEGIN", "CHECK", and "use" blocks, because these are
          considered as occurring outside the execution of your
          program.  "INIT" and "END" blocks, however, will be

     -dt  runs the program under the Perl debugger.  See perlde-
          bug. If t is specified, it indicates to the debugger
          that threads will be used in the code being debugged.

          runs the program under the control of a debugging, pro-
          filing, or tracing module installed as Devel::foo.
          E.g., -d:DProf executes the program using the
          Devel::DProf profiler.  As with the -M flag, options
          may be passed to the Devel::foo package where they will
          be received and interpreted by the Devel::foo::import
          routine. The comma-separated list of options must fol-
          low a "=" character. If t is specified, it indicates to
          the debugger that threads will be used in the code
          being debugged. See perldebug.

          sets debugging flags.  To watch how it executes your
          program, use -Dtls.  (This works only if debugging is
          compiled into your Perl.)  Another nice value is -Dx,
          which lists your compiled syntax tree.  And -Dr
          displays compiled regular expressions; the format of
          the output is explained in perldebguts.

          As an alternative, specify a number instead of list of
          letters (e.g., -D14 is equivalent to -Dtls):

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                  1  p  Tokenizing and parsing
                  2  s  Stack snapshots (with v, displays all stacks)
                  4  l  Context (loop) stack processing
                  8  t  Trace execution
                 16  o  Method and overloading resolution
                 32  c  String/numeric conversions
                 64  P  Print profiling info, preprocessor command for -P, source file input state
                128  m  Memory allocation
                256  f  Format processing
                512  r  Regular expression parsing and execution
               1024  x  Syntax tree dump
               2048  u  Tainting checks
               4096     (Obsolete, previously used for LEAKTEST)
               8192  H  Hash dump -- usurps values()
              16384  X  Scratchpad allocation
              32768  D  Cleaning up
              65536  S  Thread synchronization
             131072  T  Tokenising
             262144  R  Include reference counts of dumped variables (eg when using -Ds)
             524288  J  Do not s,t,P-debug (Jump over) opcodes within package DB
            1048576  v  Verbose: use in conjunction with other flags
            8388608  q  quiet - currently only suppresses the "EXECUTING" message

          All these flags require -DDEBUGGING when you compile
          the Perl executable (but see Devel::Peek, re which may
          change this). See the INSTALL file in the Perl source
          distribution for how to do this.  This flag is automat-
          ically set if you include -g option when "Configure"
          asks you about optimizer/debugger flags.

          If you're just trying to get a print out of each line
          of Perl code as it executes, the way that "sh -x" pro-
          vides for shell scripts, you can't use Perl's -D
          switch.  Instead do this

            # If you have "env" utility
            env PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program

            # Bourne shell syntax
            $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program

            # csh syntax
            % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)

          See perldebug for details and variations.

     -e commandline
          may be used to enter one line of program.  If -e is
          given, Perl will not look for a filename in the argu-
          ment list.  Multiple -e commands may be given to build
          up a multi-line script.  Make sure to use semicolons
          where you would in a normal program.

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     -f   Disable executing $Config{sitelib}/sitecustomize.pl at

          Perl can be built so that it by default will try to
          execute $Config{sitelib}/sitecustomize.pl at startup.
          This is a hook that allows the sysadmin to customize
          how perl behaves.  It can for instance be used to add
          entries to the @INC array to make perl find modules in
          non-standard locations.

          specifies the pattern to split on if -a is also in
          effect.  The pattern may be surrounded by "//", "", or
          '', otherwise it will be put in single quotes. You
          can't use literal whitespace in the pattern.

     -h   prints a summary of the options.

          specifies that files processed by the "<>" construct
          are to be edited in-place.  It does this by renaming
          the input file, opening the output file by the original
          name, and selecting that output file as the default for
          print() statements.  The extension, if supplied, is
          used to modify the name of the old file to make a
          backup copy, following these rules:

          If no extension is supplied, no backup is made and the
          current file is overwritten.

          If the extension doesn't contain a "*", then it is
          appended to the end of the current filename as a suf-
          fix.  If the extension does contain one or more "*"
          characters, then each "*" is replaced with the current
          filename.  In Perl terms, you could think of this as:

              ($backup = $extension) =~ s/\*/$file_name/g;

          This allows you to add a prefix to the backup file,
          instead of (or in addition to) a suffix:

              $ perl -pi'orig_*' -e 's/bar/baz/' fileA    # backup to 'orig_fileA'

          Or even to place backup copies of the original files
          into another directory (provided the directory already

              $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'

          These sets of one-liners are equivalent:

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              $ perl -pi -e 's/bar/baz/' fileA            # overwrite current file
              $ perl -pi'*' -e 's/bar/baz/' fileA         # overwrite current file

              $ perl -pi'.orig' -e 's/bar/baz/' fileA     # backup to 'fileA.orig'
              $ perl -pi'*.orig' -e 's/bar/baz/' fileA    # backup to 'fileA.orig'

          From the shell, saying

              $ perl -p -i.orig -e "s/foo/bar/; ... "

          is the same as using the program:

              #!/usr/bin/perl -pi.orig

          which is equivalent to

              $extension = '.orig';
              LINE: while (<>) {
                  if ($ARGV ne $oldargv) {
                      if ($extension !~ /\*/) {
                          $backup = $ARGV . $extension;
                      else {
                          ($backup = $extension) =~ s/\*/$ARGV/g;
                      rename($ARGV, $backup);
                      open(ARGVOUT, ">$ARGV");
                      $oldargv = $ARGV;
              continue {
                  print;  # this prints to original filename

          except that the -i form doesn't need to compare $ARGV
          to $oldargv to know when the filename has changed.  It
          does, however, use ARGVOUT for the selected filehandle.
          Note that STDOUT is restored as the default output
          filehandle after the loop.

          As shown above, Perl creates the backup file whether or
          not any output is actually changed.  So this is just a
          fancy way to copy files:

              $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
              $ perl -p -i'.orig' -e 1 file1 file2 file3...

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          You can use "eof" without parentheses to locate the end
          of each input file, in case you want to append to each
          file, or reset line numbering (see example in "eof" in

          If, for a given file, Perl is unable to create the
          backup file as specified in the extension then it will
          skip that file and continue on with the next one (if it

          For a discussion of issues surrounding file permissions
          and -i, see "Why does Perl let me delete read-only
          files? Why does -i clobber protected files? Isn't this
          a bug in Perl?" in perlfaq5.

          You cannot use -i to create directories or to strip
          extensions from files.

          Perl does not expand "~" in filenames, which is good,
          since some folks use it for their backup files:

              $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...

          Note that because -i renames or deletes the original
          file before creating a new file of the same name, UNIX-
          style soft and hard links will not be preserved.

          Finally, the -i switch does not impede execution when
          no files are given on the command line.  In this case,
          no backup is made (the original file cannot, of course,
          be determined) and processing proceeds from STDIN to
          STDOUT as might be expected.

          Directories specified by -I are prepended to the search
          path for modules (@INC), and also tells the C prepro-
          cessor where to search for include files.  The C
          preprocessor is invoked with -P; by default it searches
          /usr/include and /usr/lib/perl.

          enables automatic line-ending processing.  It has two
          separate effects.  First, it automatically chomps $/
          (the input record separator) when used with -n or -p.
          Second, it assigns "$\" (the output record separator)
          to have the value of octnum so that any print state-
          ments will have that separator added back on. If octnum
          is omitted, sets "$\" to the current value of $/.  For
          instance, to trim lines to 80 columns:

              perl -lpe 'substr($_, 80) = ""'

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          Note that the assignment "$\ = $/" is done when the
          switch is processed, so the input record separator can
          be different than the output record separator if the -l
          switch is followed by a -0 switch:

              gnufind / -print0 | perl -ln0e 'print "found $_" if -p'

          This sets "$\" to newline and then sets $/ to the null

     -M[-]'module ...'
          -mmodule executes "use" module "();" before executing
          your program.

          -Mmodule executes "use" module ";" before executing
          your program.  You can use quotes to add extra code
          after the module name, e.g., '-Mmodule qw(foo bar)'.

          If the first character after the -M or -m is a dash
          ("-") then the 'use' is replaced with 'no'.

          A little builtin syntactic sugar means you can also say
          -mmodule=foo,bar or -Mmodule=foo,bar as a shortcut for
          '-Mmodule qw(foo bar)'.  This avoids the need to use
          quotes when importing symbols.  The actual code gen-
          erated by -Mmodule=foo,bar is "use module
          split(/,/,q{foo,bar})".  Note that the "=" form removes
          the distinction between -m and -M.

          A consequence of this is that -MFoo=number never does a
          version check (unless "Foo::import()" itself is set up
          to do a version check, which could happen for example
          if Foo inherits from Exporter.)

     -n   causes Perl to assume the following loop around your
          program, which makes it iterate over filename arguments
          somewhat like sed -n or awk:

              while (<>) {
                  ...             # your program goes here

          Note that the lines are not printed by default.  See -p
          to have lines printed.  If a file named by an argument
          cannot be opened for some reason, Perl warns you about
          it and moves on to the next file.

          Here is an efficient way to delete all files that

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          haven't been modified for at least a week:

              find . -mtime +7 -print | perl -nle unlink

          This is faster than using the -exec switch of find
          because you don't have to start a process on every
          filename found.  It does suffer from the bug of mishan-
          dling newlines in pathnames, which you can fix if you
          follow the example under -0.

          "BEGIN" and "END" blocks may be used to capture control
          before or after the implicit program loop, just as in

     -p   causes Perl to assume the following loop around your
          program, which makes it iterate over filename arguments
          somewhat like sed:

              while (<>) {
                  ...             # your program goes here
              } continue {
                  print or die "-p destination: $!\n";

          If a file named by an argument cannot be opened for
          some reason, Perl warns you about it, and moves on to
          the next file.  Note that the lines are printed
          automatically.  An error occurring during printing is
          treated as fatal.  To suppress printing use the -n
          switch.  A -p overrides a -n switch.

          "BEGIN" and "END" blocks may be used to capture control
          before or after the implicit loop, just as in awk.

     -P   NOTE: Use of -P is strongly discouraged because of its
          inherent problems, including poor portability.

          This option causes your program to be run through the C
          preprocessor before compilation by Perl.  Because both
          comments and cpp directives begin with the # character,
          you should avoid starting comments with any words
          recognized by the C preprocessor such as "if", "else",
          or "define".

          If you're considering using "-P", you might also want
          to look at the Filter::cpp module from CPAN.

          The problems of -P include, but are not limited to:

          *         The "#!" line is stripped, so any switches
                    there don't apply.

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          *         A "-P" on a "#!" line doesn't work.

          *         All lines that begin with (whitespace and) a
                    "#" but do not look like cpp commands, are
                    stripped, including anything inside Perl
                    strings, regular expressions, and here-docs .

          *         In some platforms the C preprocessor knows
                    too much: it knows about the C++ -style
                    until-end-of-line comments starting with
                    "//". This will cause problems with common
                    Perl constructs like


                    because after -P this will became illegal


                    The workaround is to use some other quoting
                    separator than "/", like for example "!":


          *         It requires not only a working C preprocessor
                    but also a working sed.  If not on UNIX, you
                    are probably out of luck on this.

          *         Script line numbers are not preserved.

          *         The "-x" does not work with "-P".

     -s   enables rudimentary switch parsing for switches on the
          command line after the program name but before any
          filename arguments (or before an argument of --).  Any
          switch found there is removed from @ARGV and sets the
          corresponding variable in the Perl program.  The fol-
          lowing program prints "1" if the program is invoked
          with a -xyz switch, and "abc" if it is invoked with

              #!/usr/bin/perl -s
              if ($xyz) { print "$xyz\n" }

          Do note that a switch like --help creates the variable
          ${-help}, which is not compliant with "strict refs".
          Also, when using this option on a script with warnings
          enabled you may get a lot of spurious "used only once"

     -S   makes Perl use the PATH environment variable to search

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          for the program (unless the name of the program con-
          tains directory separators).

          On some platforms, this also makes Perl append suffixes
          to the filename while searching for it.  For example,
          on Win32 platforms, the ".bat" and ".cmd" suffixes are
          appended if a lookup for the original name fails, and
          if the name does not already end in one of those suf-
          fixes.  If your Perl was compiled with DEBUGGING turned
          on, using the -Dp switch to Perl shows how the search

          Typically this is used to emulate #! startup on plat-
          forms that don't support #!.  Its also convenient when
          debugging a script that uses #!, and is thus normally
          found by the shell's $PATH search mechanism.

          This example works on many platforms that have a shell
          compatible with Bourne shell:

              eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
                      if $running_under_some_shell;

          The system ignores the first line and feeds the program
          to /bin/sh, which proceeds to try to execute the Perl
          program as a shell script. The shell executes the
          second line as a normal shell command, and thus starts
          up the Perl interpreter.  On some systems $0 doesn't
          always contain the full pathname, so the -S tells Perl
          to search for the program if necessary.  After Perl
          locates the program, it parses the lines and ignores
          them because the variable $running_under_some_shell is
          never true.  If the program will be interpreted by csh,
          you will need to replace "${1+"$@"}" with $*, even
          though that doesn't understand embedded spaces (and
          such) in the argument list.  To start up sh rather than
          csh, some systems may have to replace the #! line with
          a line containing just a colon, which will be politely
          ignored by Perl.  Other systems can't control that, and
          need a totally devious construct that will work under
          any of csh, sh, or Perl, such as the following:

                  eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
                  & eval 'exec /usr/bin/perl -wS $0 $argv:q'
                          if $running_under_some_shell;

          If the filename supplied contains directory separators
          (i.e., is an absolute or relative pathname), and if
          that file is not found, platforms that append file
          extensions will do so and try to look for the file with
          those extensions added, one by one.

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          On DOS-like platforms, if the program does not contain
          directory separators, it will first be searched for in
          the current directory before being searched for on the
          PATH.  On Unix platforms, the program will be searched
          for strictly on the PATH.

     -t   Like -T, but taint checks will issue warnings rather
          than fatal errors.  These warnings can be controlled
          normally with "no warnings qw(taint)".

          NOTE: this is not a substitute for -T. This is meant
          only to be used as a temporary development aid while
          securing legacy code: for real production code and for
          new secure code written from scratch always use the
          real -T.

     -T   forces "taint" checks to be turned on so you can test
          them.  Ordinarily these checks are done only when run-
          ning setuid or setgid.  It's a good idea to turn them
          on explicitly for programs that run on behalf of some-
          one else whom you might not necessarily trust, such as
          CGI programs or any internet servers you might write in
          Perl.  See perlsec for details.  For security reasons,
          this option must be seen by Perl quite early; usually
          this means it must appear early on the command line or
          in the #! line for systems which support that con-

     -u   This obsolete switch causes Perl to dump core after
          compiling your program.  You can then in theory take
          this core dump and turn it into an executable file by
          using the undump program (not supplied). This speeds
          startup at the expense of some disk space (which you
          can minimize by stripping the executable).  (Still, a
          "hello world" executable comes out to about 200K on my
          machine.)  If you want to execute a portion of your
          program before dumping, use the dump() operator
          instead.  Note: availability of undump is platform
          specific and may not be available for a specific port
          of Perl.

          This switch has been superseded in favor of the new
          Perl code generator backends to the compiler.  See B
          and B::Bytecode for details.

     -U   allows Perl to do unsafe operations.  Currently the
          only "unsafe" operations are attempting to unlink
          directories while running as superuser, and running
          setuid programs with fatal taint checks turned into
          warnings.  Note that the -w switch (or the $^W vari-
          able) must be used along with this option to actually
          generate the taint-check warnings.

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     -v   prints the version and patchlevel of your perl execut-

     -V   prints summary of the major perl configuration values
          and the current values of @INC.

          Prints to STDOUT the value of the named configuration
          variable(s), with multiples when your configvar argu-
          ment looks like a regex (has non-letters).  For exam-

              $ perl -V:libc
              $ perl -V:lib.
                  libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
              $ perl -V:lib.*
                  libpth='/usr/local/lib /lib /usr/lib';
                  libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';

          Additionally, extra colons can be used to control for-
          matting.  A trailing colon suppresses the linefeed and
          terminator ';', allowing you to embed queries into
          shell commands.  (mnemonic: PATH separator ':'.)

              $ echo "compression-vars: " `perl -V:z.*: ` " are here !"
              compression-vars:  zcat='' zip='zip'  are here !

          A leading colon removes the 'name=' part of the
          response, this allows you to map to the name you need.
          (mnemonic: empty label)

              $ echo "goodvfork="`./perl -Ilib -V::usevfork`

          Leading and trailing colons can be used together if you
          need positional parameter values without the names.
          Note that in the case below, the PERL_API params are
          returned in alphabetical order.

              $ echo building_on `perl -V::osname: -V::PERL_API_.*:` now
              building_on 'linux' '5' '1' '9' now

     -w   prints warnings about dubious constructs, such as vari-
          able names that are mentioned only once and scalar
          variables that are used before being set, redefined
          subroutines, references to undefined filehandles or

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          filehandles opened read-only that you are attempting to
          write on, values used as a number that don't look like
          numbers, using an array as though it were a scalar, if
          your subroutines recurse more than 100 deep, and innu-
          merable other things.

          This switch really just enables the internal $^W vari-
          able.  You can disable or promote into fatal errors
          specific warnings using "__WARN__" hooks, as described
          in perlvar and "warn" in perlfunc. See also perldiag
          and perltrap.  A new, fine-grained warning facility is
          also available if you want to manipulate entire classes
          of warnings; see warnings or perllexwarn.

     -W   Enables all warnings regardless of "no warnings" or
          $^W. See perllexwarn.

     -X   Disables all warnings regardless of "use warnings" or
          $^W. See perllexwarn.

     -x directory
          tells Perl that the program is embedded in a larger
          chunk of unrelated ASCII text, such as in a mail mes-
          sage.  Leading garbage will be discarded until the
          first line that starts with #! and contains the string
          "perl".  Any meaningful switches on that line will be
          applied. If a directory name is specified, Perl will
          switch to that directory before running the program.
          The -x switch controls only the disposal of leading
          garbage.  The program must be terminated with "__END__"
          if there is trailing garbage to be ignored (the program
          can process any or all of the trailing garbage via the
          DATA filehandle if desired).


     HOME        Used if chdir has no argument.

     LOGDIR      Used if chdir has no argument and HOME is not

     PATH        Used in executing subprocesses, and in finding
                 the program if -S is used.

     PERL5LIB    A list of directories in which to look for Perl
                 library files before looking in the standard
                 library and the current directory.  Any
                 architecture-specific directories under the
                 specified locations are automatically included
                 if they exist.  If PERL5LIB is not defined,
                 PERLLIB is used.  Directories are separated
                 (like in PATH) by a colon on unixish platforms

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                 and by a semicolon on Windows (the proper path
                 separator being given by the command "perl

                 When running taint checks (either because the
                 program was running setuid or setgid, or the -T
                 switch was used), neither variable is used. The
                 program should instead say:

                     use lib "/my/directory";

     PERL5OPT    Command-line options (switches).  Switches in
                 this variable are taken as if they were on every
                 Perl command line.  Only the -[DIMUdmtw]
                 switches are allowed.  When running taint checks
                 (because the program was running setuid or set-
                 gid, or the -T switch was used), this variable
                 is ignored.  If PERL5OPT begins with -T, taint-
                 ing will be enabled, and any subsequent options

     PERLIO      A space (or colon) separated list of PerlIO
                 layers. If perl is built to use PerlIO system
                 for IO (the default) these layers effect perl's

                 It is conventional to start layer names with a
                 colon e.g. ":perlio" to emphasise their similar-
                 ity to variable "attributes". But the code that
                 parses layer specification strings (which is
                 also used to decode the PERLIO environment vari-
                 able) treats the colon as a separator.

                 An unset or empty PERLIO is equivalent to

                 The list becomes the default for all perl's IO.
                 Consequently only built-in layers can appear in
                 this list, as external layers (such as :encod-
                 ing()) need IO in  order to load them!. See
                 "open pragma" for how to add external encodings
                 as defaults.

                 The layers that it makes sense to include in the
                 PERLIO environment variable are briefly summar-
                 ised below. For more details see PerlIO.

                 :bytes  A pseudolayer that turns off the ":utf8"
                         flag for the layer below. Unlikely to be
                         useful on its own in the global PERLIO
                         environment variable. You perhaps were
                         thinking of ":crlf:bytes" or

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                 :crlf   A layer which does CRLF to "\n" transla-
                         tion distinguishing "text" and "binary"
                         files in the manner of MS-DOS and simi-
                         lar operating systems. (It currently
                         does not mimic MS-DOS as far as treating
                         of Control-Z as being an end-of-file

                 :mmap   A layer which implements "reading" of
                         files by using "mmap()" to make (whole)
                         file appear in the process's address
                         space, and then using that as PerlIO's

                 :perlio This is a re-implementation of
                         "stdio-like" buffering written as a Per-
                         lIO "layer".  As such it will call what-
                         ever layer is below it for its opera-
                         tions (typically ":unix").

                 :pop    An experimental pseudolayer that removes
                         the topmost layer. Use with the same
                         care as is reserved for nitroglycerin.

                 :raw    A pseudolayer that manipulates other
                         layers.  Applying the ":raw" layer is
                         equivalent to calling "binmode($fh)".
                         It makes the stream pass each byte as-is
                         without any translation.  In particular
                         CRLF translation, and/or :utf8 intuited
                         from locale are disabled.

                         Unlike in the earlier versions of Perl
                         ":raw" is not just the inverse of
                         ":crlf" - other layers which would
                         affect the binary nature of the stream
                         are also removed or disabled.

                 :stdio  This layer provides PerlIO interface by
                         wrapping system's ANSI C "stdio" library
                         calls. The layer provides both buffering
                         and IO. Note that ":stdio" layer does
                         not do CRLF translation even if that is
                         platforms normal behaviour. You will
                         need a ":crlf" layer above it to do

                 :unix   Low level layer which calls "read",
                         "write" and "lseek" etc.

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                 :utf8   A pseudolayer that turns on a flag on
                         the layer below to tell perl that output
                         should be in utf8 and that input should
                         be regarded as already in utf8 form.
                         May be useful in PERLIO environment
                         variable to make UTF-8 the default. (To
                         turn off that behaviour use ":bytes"

                 :win32  On Win32 platforms this experimental
                         layer uses native "handle" IO rather
                         than unix-like numeric file descriptor
                         layer. Known to be buggy in this

                 On all platforms the default set of layers
                 should give acceptable results.

                 For UNIX platforms that will equivalent of "unix
                 perlio" or "stdio". Configure is setup to prefer
                 "stdio" implementation if system's library pro-
                 vides for fast access to the buffer, otherwise
                 it uses the "unix perlio" implementation.

                 On Win32 the default in this release is "unix
                 crlf". Win32's "stdio" has a number of
                 bugs/mis-features for perl IO which are somewhat
                 C compiler vendor/version dependent. Using our
                 own "crlf" layer as the buffer avoids those
                 issues and makes things more uniform. The "crlf"
                 layer provides CRLF to/from "\n" conversion as
                 well as buffering.

                 This release uses "unix" as the bottom layer on
                 Win32 and so still uses C compiler's numeric
                 file descriptor routines. There is an experimen-
                 tal native "win32" layer which is expected to be
                 enhanced and should eventually be the default
                 under Win32.

                 If set to the name of a file or device then cer-
                 tain operations of PerlIO sub-system will be
                 logged to that file (opened as append). Typical
                 uses are UNIX:

                    PERLIO_DEBUG=/dev/tty perl script ...

                 and Win32 approximate equivalent:

                    set PERLIO_DEBUG=CON
                    perl script ...

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                 This functionality is disabled for setuid
                 scripts and for scripts run with -T.

     PERLLIB     A list of directories in which to look for Perl
                 library files before looking in the standard
                 library and the current directory. If PERL5LIB
                 is defined, PERLLIB is not used.

     PERL5DB     The command used to load the debugger code.  The
                 default is:

                         BEGIN { require 'perl5db.pl' }

                 If set to a true value, indicates to the
                 debugger that the code being debugged uses

     PERL5SHELL (specific to the Win32 port)
                 May be set to an alternative shell that perl
                 must use internally for executing "backtick"
                 commands or system().  Default is "cmd.exe
                 /x/d/c" on WindowsNT and "command.com /c" on
                 Windows95.  The value is considered to be
                 space-separated.  Precede any character that
                 needs to be protected (like a space or
                 backslash) with a backslash.

                 Note that Perl doesn't use COMSPEC for this pur-
                 pose because COMSPEC has a high degree of varia-
                 bility among users, leading to portability con-
                 cerns.  Besides, perl can use a shell that may
                 not be fit for interactive use, and setting COM-
                 SPEC to such a shell may interfere with the
                 proper functioning of other programs (which usu-
                 ally look in COMSPEC to find a shell fit for
                 interactive use).

     PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
                 Set to 1 to allow the use of non-IFS compatible
                 LSP's. Perl normally searches for an IFS-
                 compatible LSP because this is required for its
                 emulation of Windows sockets as real filehan-
                 dles.  However, this may cause problems if you
                 have a firewall such as McAfee Guardian which
                 requires all applications to use its LSP which
                 is not IFS-compatible, because clearly Perl will
                 normally avoid using such an LSP. Setting this
                 environment variable to 1 means that Perl will
                 simply use the first suitable LSP enumerated in
                 the catalog, which keeps McAfee Guardian happy
                 (and in that particular case Perl still works

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                 too because McAfee Guardian's LSP actually plays
                 some other games which allow applications
                 requiring IFS compatibility to work).

                 Relevant only if perl is compiled with the mal-
                 loc included with the perl distribution (that
                 is, if "perl -V:d_mymalloc" is 'define'). If
                 set, this causes memory statistics to be dumped
                 after execution.  If set to an integer greater
                 than one, also causes memory statistics to be
                 dumped after compilation.

                 Relevant only if your perl executable was built
                 with -DDEBUGGING, this controls the behavior of
                 global destruction of objects and other refer-
                 ences.  See "PERL_DESTRUCT_LEVEL" in perlhack
                 for more information.

                 Set to one to have perl resolve all undefined
                 symbols when it loads a dynamic library.  The
                 default behaviour is to resolve symbols when
                 they are used.  Setting this variable is useful
                 during testing of extensions as it ensures that
                 you get an error on misspelled function names
                 even if the test suite doesn't call it.

                 If using the "encoding" pragma without an expli-
                 cit encoding name, the PERL_ENCODING environment
                 variable is consulted for an encoding name.

                 (Since Perl 5.8.1.)  Used to randomise Perl's
                 internal hash function. To emulate the pre-5.8.1
                 behaviour, set to an integer (zero means exactly
                 the same order as 5.8.0).  "Pre-5.8.1" means,
                 among other things, that hash keys will be
                 ordered the same between different runs of Perl.

                 The default behaviour is to randomise unless the
                 PERL_HASH_SEED is set. If Perl has been compiled
                 with "-DUSE_HASH_SEED_EXPLICIT", the default
                 behaviour is not to randomise unless the
                 PERL_HASH_SEED is set.

                 If PERL_HASH_SEED is unset or set to a non-
                 numeric string, Perl uses the pseudorandom seed
                 supplied by the operating system and libraries.
                 This means that each different run of Perl will

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                 have a different ordering of the results of
                 keys(), values(), and each().

                 Please note that the hash seed is sensitive
                 information. Hashes are randomized to protect
                 against local and remote attacks against Perl
                 code. By manually setting a seed this protection
                 may be partially or completely lost.

                 See "Algorithmic Complexity Attacks" in perlsec
                 and "PERL_HASH_SEED_DEBUG" for more information.

                 (Since Perl 5.8.1.)  Set to one to display (to
                 STDERR) the value of the hash seed at the begin-
                 ning of execution.  This, combined with
                 "PERL_HASH_SEED" is intended to aid in debugging
                 nondeterministic behavior caused by hash random-

                 Note that the hash seed is sensitive informa-
                 tion: by knowing it one can craft a denial-of-
                 service attack against Perl code, even remotely,
                 see "Algorithmic Complexity Attacks" in perlsec
                 for more information. Do not disclose the hash
                 seed to people who don't need to know it. See
                 also hash_seed() of Hash::Util.

     PERL_ROOT (specific to the VMS port)
                 A translation concealed rooted logical name that
                 contains perl and the logical device for the
                 @INC path on VMS only.  Other logical names that
                 affect perl on VMS include PERLSHR,
                 but are optional and discussed further in
                 perlvms and in README.vms in the Perl source

                 In Perls 5.8.1 and later.  If set to "unsafe"
                 the pre-Perl-5.8.0 signals behaviour (immediate
                 but unsafe) is restored.  If set to "safe" the
                 safe (or deferred) signals are used. See
                 "Deferred Signals (Safe Signals)" in perlipc.

                 Equivalent to the -C command-line switch.  Note
                 that this is not a boolean variable-- setting
                 this to "1" is not the right way to "enable
                 Unicode" (whatever that would mean).  You can
                 use "0" to "disable Unicode", though (or alter-
                 natively unset PERL_UNICODE in your shell before

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                 starting Perl).  See the description of the "-C"
                 switch for more information.

     SYS$LOGIN (specific to the VMS port)
                 Used if chdir has no argument and HOME and LOG-
                 DIR are not set.

     Perl also has environment variables that control how Perl
     handles data specific to particular natural languages.  See

     Apart from these, Perl uses no other environment variables,
     except to make them available to the program being executed,
     and to child processes.  However, programs running setuid
     would do well to execute the following lines before doing
     anything else, just to keep people honest:

         $ENV{PATH}  = '/bin:/usr/bin';    # or whatever you need
         $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
         delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};

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