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

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

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

NNAAMMEE #

 perlrun - how to execute the Perl interpreter

SSYYNNOOPPSSIISS #

 ppeerrll [ --ggssTTttuuUUWWXX ]      [ --hh??vv ] [ --VV[:_c_o_n_f_i_g_v_a_r] ]
    [ --ccww ] [ --dd[tt][:_d_e_b_u_g_g_e_r] ] [ --DD[_n_u_m_b_e_r_/_l_i_s_t] ]
  [ --ppnnaa ] [ --FF_p_a_t_t_e_r_n ] [ --ll[_o_c_t_a_l] ] [ --00[_o_c_t_a_l_/_h_e_x_a_d_e_c_i_m_a_l] ]
   [ --II_d_i_r ] [ --mm[--]_m_o_d_u_l_e ] [ --MM[--]_'_m_o_d_u_l_e_._._._' ] [ --ff ]
  [ --CC  [[_nn_uu_mm_bb_ee_rr_//_ll_ii_ss_tt]]  ]      [ --SS ]      [ --xx[_d_i_r] ]      [ --ii[_e_x_t_e_n_s_i_o_n] ]
   [ [--ee|--EE] _'_c_o_m_m_a_n_d_' ] [ ---- ] [ _p_r_o_g_r_a_m_f_i_l_e ] [ _a_r_g_u_m_e_n_t ]...

DDEESSCCRRIIPPTTIIOONN #

 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 or -E switches on the command line.

 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 Perl".)

 3.  Passed in implicitly via standard input.  This works only if there
     are no filename arguments--to pass arguments 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 message.  (In this case you would indicate the end of the program
 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 recognize the "#!" line, you still
 can get consistent switch behaviour 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 characters, some switches may be
 passed in on the command line, and some may not; you could even get a "-"
 without its 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 standard 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 --00_d_i_g_i_t_s by
 "BEGIN{ $/ = "\0digits"; }".

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

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

 to let Perl see the "-p" switch.

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

     #!/usr/bin/env perl

 The examples above use a relative path to the perl interpreter, getting
 whatever version is first in the user's path.  If you want a specific
 version of Perl, say, perl5.14.1, you should place that directly in the
 "#!" line's path.

 If the "#!" line does not contain the word "perl" nor the word "indir",
 the program named after the "#!" is executed instead of the Perl
 interpreter.  This is slightly bizarre, but it helps people on machines
 that don't do "#!", because they can tell a program that their SHELL is
 _/_u_s_r_/_b_i_n_/_p_e_r_l, and Perl will then dispatch the program to the correct
 interpreter for them.

 After locating your program, Perl compiles the entire program 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 eexxiitt(()) or ddiiee(()) operator, an implicit
 exit(0) is provided to indicate successful completion.

##!! aanndd qquuoottiinngg oonn nnoonn--UUnniixx ssyysstteemmss Unix’s “#!” technique can be simulated on other systems:

OS/2 #

     Put

         extproc perl -S -your_switches

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

MS-DOS #

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

 Win95/NT
     The Win95/NT installation, when using the ActiveState installer for
     Perl, will modify the Registry to associate the _._p_l 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 difference
     between an executable Perl program and a Perl library file.

 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 --mmyyssww 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 _D_C_L_$_P_A_T_H 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 "-V:startperl"".

 Command-interpreters on non-Unix systems have rather different ideas on
 quoting than Unix shells.  You'll need to 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 _n_o_t do on Unix or Plan 9 systems.  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\""

# 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 _4_D_O_S were the command
 shell, this would probably work better:

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

 CCMMDD..EEXXEE in Windows NT slipped a lot of standard Unix functionality in
 when nobody was looking, but just try to find documentation for its
 quoting rules.

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

LLooccaattiioonn ooff PPeerrll It may seem obvious to say, but Perl is useful only when users can easily find it. When possible, it’s good for both _/_u_s_r_/_b_i_n_/_p_e_r_l and _/_u_s_r_/_l_o_c_a_l_/_b_i_n_/_p_e_r_l 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 place.

 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.

     #!/usr/local/bin/perl5.14

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

     use v5.14;

CCoommmmaanndd SSwwiittcchheess 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

 A "--" signals the end of options and disables further option processing.
 Any arguments after the "--" are treated as filenames and arguments.

 Switches include:

 --00[_o_c_t_a_l_/_h_e_x_a_d_e_c_i_m_a_l]
      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 _f_i_n_d 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.

      Any value 0400 or above will cause Perl to slurp files whole, but by
      convention the value 0777 is the one normally used for this purpose.
      The "-g" flag is a simpler alias for it.

      You can also specify the separator character using hexadecimal
      notation: --00xx_HH_HH_HH_.._.._.., where the "_H" are valid hexadecimal digits.
      Unlike the octal form, this one may be used to specify any Unicode
      character, even those beyond 0xFF.  So if you _r_e_a_l_l_y want a record
      separator of 0777, specify it as --00xx11FFFF.  (This means that you
      cannot use the "-x" option with a directory name that consists of
      hexadecimal digits, or else Perl will think you have specified a hex
      number to --00.)

 --aa   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

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

      An alternate delimiter may be specified using -F.

      --aa implicitly sets "-n".

 --CC [[_nn_uu_mm_bb_ee_rr_//_ll_ii_ss_tt]]
      The --CC flag controls some of the Perl Unicode features.

      As of 5.8.1, the --CC 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_CTYPE, and LANG, in the order of
                    decreasing precedence) -- if the variables indicate
                    UTF-8, then the selected "IOEioA" are in effect
          a   256   Set ${^UTF8CACHE} to -1, to run the UTF-8 caching
                    code in debugging mode.

      For example, --CCOOEE and --CC66 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 ooppeenn(()) (or similar I/O
      operations) in main program scope 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 produced to any output stream.  This
      is just the default set via "${^OPEN}", with explicit layers in
      ooppeenn(()) and with bbiinnmmooddee(()) one can manipulate streams as usual.  This
      has no effect on code run in modules.

      --CC 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 --CCSSDDLL.  In other words, the standard I/O handles and
      the default "open()" layer are UTF-8-fied _b_u_t only if the locale
      environment variables indicate a UTF-8 locale.  This behaviour
      follows the _i_m_p_l_i_c_i_t (and problematic) UTF-8 behaviour of Perl
      5.8.0.  (See "UTF-8 no longer default under UTF-8 locales" in
      perl581delta.)

      You can use --CC00 (or "0" for "PERL_UNICODE") to explicitly disable
      all the above Unicode features.

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

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

      NNoottee:: Since perl 5.10.1, if the --CC option is used on the "#!" line,
      it must be specified on the command line as well, since the standard
      streams are already set up at this point in the execution of the
      perl interpreter.  You can also use bbiinnmmooddee(()) to set the encoding of
      an I/O stream.

 --cc   causes Perl to check the syntax of the program and then exit without
      executing it.  Actually, it _w_i_l_l execute any "BEGIN", "UNITCHECK",
      or "CHECK" blocks and any "use" statements: these are considered as
      occurring outside the execution of your program.  "INIT" and "END"
      blocks, however, will be skipped.

 --dd
 --ddtt  runs the program under the Perl debugger.  See perldebug.  If tt is
      specified, it indicates to the debugger that threads will be used in
      the code being debugged.

 --dd::_M_O_D_[_=_b_a_r_,_b_a_z_]
 --ddtt::_M_O_D_[_=_b_a_r_,_b_a_z_]
      runs the program under the control of a debugging, profiling, or
      tracing module installed as "Devel::_M_O_D". E.g., --dd::DDPPrrooff executes
      the program using the "Devel::DProf" profiler.  As with the -M flag,
      options may be passed to the "Devel::_M_O_D" package where they will be
      received and interpreted by the "Devel::_M_O_D::import" routine.
      Again, like --MM, use ---dd::--_MM_OO_DD to call "Devel::_M_O_D::unimport" instead
      of import.  The comma-separated list of options must follow a "="
      character.  If tt is specified, it indicates to the debugger that
      threads will be used in the code being debugged.  See perldebug.

 --DD_l_e_t_t_e_r_s
 --DD_n_u_m_b_e_r
      sets debugging flags. This switch is enabled only if your perl
      binary has been built with debugging enabled: normal production
      perls won't have been.

      For example, to watch how perl executes your program, use --DDttllss.
      Another nice value is --DDxx, which lists your compiled syntax tree,
      and --DDrr 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., --DD1144 is equivalent to --DDttllss):

               1  p  Tokenizing and parsing (with v, displays parse
                     stack)
               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, source file input state
             128  m  Memory and SV allocation
             256  f  Format processing
             512  r  Regular expression parsing and execution
            1024  x  Syntax tree dump
            2048  u  Tainting checks
            4096  U  Unofficial, User hacking (reserved for private,
                     unreleased use)
            8192  h  Show hash randomization debug output (changes to
                     PL_hash_rand_bits and their origin)
           16384  X  Scratchpad allocation
           32768  D  Cleaning up
           65536  S  Op slab allocation
          131072  T  Tokenizing
          262144  R  Include reference counts of dumped variables
                     (eg when using -Ds)
          524288  J  show s,t,P-debug (don't Jump over) on opcodes within
                     package DB
         1048576  v  Verbose: use in conjunction with other flags to
                     increase the verbosity of the output.  Is a no-op on
                     many of the other flags
         2097152  C  Copy On Write
         4194304  A  Consistency checks on internal structures
         8388608  q  quiet - currently only suppresses the "EXECUTING"
                     message
        16777216  M  trace smart match resolution
        33554432  B  dump suBroutine definitions, including special
                     Blocks like BEGIN
        67108864  L  trace Locale-related info; what gets output is very
                     subject to change
       134217728  i  trace PerlIO layer processing.  Set PERLIO_DEBUG to
                     the filename to trace to.
       268435456  y  trace y///, tr/// compilation and execution

      All these flags require --DDDDEEBBUUGGGGIINNGG when you compile the Perl
      executable (but see ":opd" in Devel::Peek or "'debug' mode" in re
      which may change this).  See the _I_N_S_T_A_L_L file in the Perl source
      distribution for how to do this.

      If you're just trying to get a print out of each line of Perl code
      as it executes, the way that "sh -x" provides for shell scripts, you
      can't use Perl's --DD 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.

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

 --EE _c_o_m_m_a_n_d_l_i_n_e
      behaves just like -e, except that it implicitly enables all optional
      features (in the main compilation unit). See feature.

 --ff   Disable executing _$_C_o_n_f_i_g_{_s_i_t_e_l_i_b_}_/_s_i_t_e_c_u_s_t_o_m_i_z_e_._p_l at startup.

      Perl can be built so that it by default will try to execute
      _$_C_o_n_f_i_g_{_s_i_t_e_l_i_b_}_/_s_i_t_e_c_u_s_t_o_m_i_z_e_._p_l at startup (in a BEGIN block).
      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.

      Perl actually inserts the following code:

BEGIN { #

              do { local $!; -f "$Config{sitelib}/sitecustomize.pl"; }
                  && do "$Config{sitelib}/sitecustomize.pl";
          }

      Since it is an actual "do" (not a "require"), _s_i_t_e_c_u_s_t_o_m_i_z_e_._p_l
      doesn't need to return a true value. The code is run in package
      "main", in its own lexical scope. However, if the script dies, $@
      will not be set.

      The value of $Config{sitelib} is also determined in C code and not
      read from "Config.pm", which is not loaded.

      The code is executed _v_e_r_y early. For example, any changes made to
      @INC will show up in the output of `perl -V`. Of course, "END"
      blocks will be likewise executed very late.

      To determine at runtime if this capability has been compiled in your
      perl, you can check the value of $Config{usesitecustomize}.

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

      --FF implicitly sets both "-a" and "-n".

 --gg   undefines the input record separator ($/) and thus enables the slurp
      mode. In other words, it causes Perl to read whole files at once,
      instead of line by line.

      This flag is a simpler alias for -0777.

      Mnemonics: gobble, grab, gulp.

 --hh   prints a summary of the options.

 --??   synonym for --hh: prints a summary of the options.

 --ii[_e_x_t_e_n_s_i_o_n]
      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 pprriinntt(()) 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, and your system supports it, the
      original _f_i_l_e is kept open without a name while the output is
      redirected to a new file with the original _f_i_l_e_n_a_m_e.  When perl
      exits, cleanly or not, the original _f_i_l_e is unlinked.

      If the extension doesn't contain a "*", then it is appended to the
      end of the current filename as a suffix.  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 exists):

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

      These sets of one-liners are equivalent:

       $ 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
          s/foo/bar/;

      which is equivalent to

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

      except that the --ii 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...
      or
          $ perl -p -i'.orig' -e 1 file1 file2 file3...

      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 perlfunc).

      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 exists).

      For a discussion of issues surrounding file permissions and --ii, 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 --ii 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 --ii 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 --ii 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.

 --II_d_i_r_e_c_t_o_r_y
      Directories specified by --II are prepended to the search path for
      modules (@INC).

 --ll[_o_c_t_n_u_m]
      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 _o_c_t_n_u_m so that
      any print statements will have that separator added back on.  If
      _o_c_t_n_u_m is omitted, sets "$\" to the current value of $/.  For
      instance, to trim lines to 80 columns:

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

      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 --ll 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 character.

 --mm[--]_m_o_d_u_l_e
 --MM[--]_m_o_d_u_l_e
 --MM[--]_'_m_o_d_u_l_e _._._._'
 --[[mmMM]][--]_m_o_d_u_l_e_=_a_r_g_[_,_a_r_g_]_._._.
      --mm_m_o_d_u_l_e executes "use" _m_o_d_u_l_e "();" before executing your program.
      This loads the module, but does not call its "import" method, so
      does not import subroutines and does not give effect to a pragma.

      --MM_m_o_d_u_l_e executes "use" _m_o_d_u_l_e ";" before executing your program.
      This loads the module and calls its "import" method, causing the
      module to have its default effect, typically importing subroutines
      or giving effect to a pragma.  You can use quotes to add extra code
      after the module name, e.g., '-M_M_O_D_U_L_E qw(foo bar)'.

      If the first character after the --MM or --mm is a dash (--) then the
      'use' is replaced with 'no'.  This makes no difference for --mm.

      A little builtin syntactic sugar means you can also say
      --mm_MM_OO_DD_UU_LL_EE==ffoooo,,bbaarr or --MM_MM_OO_DD_UU_LL_EE==ffoooo,,bbaarr as a shortcut for ''--MM_MM_OO_DD_UU_LL_EE
      qqww((ffoooo bbaarr))''.  This avoids the need to use quotes when importing
      symbols.  The actual code generated by --MM_MM_OO_DD_UU_LL_EE==ffoooo,,bbaarr is "use
      module split(/,/,q{foo,bar})".  Note that the "=" form removes the
      distinction between --mm and --MM; that is, --mm_MM_OO_DD_UU_LL_EE==ffoooo,,bbaarr is the same
      as --MM_MM_OO_DD_UU_LL_EE==ffoooo,,bbaarr.

      A consequence of the "split" formulation is that --MM_MM_OO_DD_UU_LL_EE==nnuummbbeerr
      never does a version check, unless "_M_O_D_U_L_E::import()" itself is set
      up to do a version check, which could happen for example if _M_O_D_U_L_E
      inherits from Exporter.

 --nn   causes Perl to assume the following loop around your program, which
      makes it iterate over filename arguments somewhat like _s_e_d _-_n or
      _a_w_k:

LINE: #

          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.

      Also note that "<>" passes command line arguments to "open" in
      perlfunc, which doesn't necessarily interpret them as file names.
      See  perlop for possible security implications.

      Here is an efficient way to delete all files that haven't been
      modified for at least a week:

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

      This is faster than using the --eexxeecc switch of _f_i_n_d because you don't
      have to start a process on every filename found (but it's not faster
      than using the --ddeelleettee switch available in newer versions of _f_i_n_d.
      It does suffer from the bug of mishandling 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 _a_w_k.

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

LINE: #

          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 --pp overrides a --nn switch.

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

 --ss   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, in the main
      package.  The following program prints "1" if the program is invoked
      with a --xxyyzz switch, and "abc" if it is invoked with --xxyyzz==aabbcc.

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

      Do note that a switch like ----hheellpp creates the variable "${-help}",
      which is not compliant with "use strict "refs"".  Also, when using
      this option on a script with warnings enabled you may get a lot of
      spurious "used only once" warnings. For these reasons, use of --ss is
      discouraged. See Getopt::Long for much more flexible switch parsing.

 --SS   makes Perl use the "PATH" environment variable to search for the
      program unless the name of the program contains path 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 suffixes.  If your Perl was compiled with "DEBUGGING" turned
      on, using the -Dp switch to Perl shows how the search progresses.

      Typically this is used to emulate "#!" startup on platforms that
      don't support "#!".  It's 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:

          #!/usr/bin/perl
          eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
                  if 0; # ^ Run only under a shell

      The system ignores the first line and feeds the program to _/_b_i_n_/_s_h,
      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 $0 doesn't
      always contain the full pathname, so the "-S" tells Perl to search
      for the program if necessary.  After Perl locates the program, it
      parses the lines and ignores them because the check 'if 0' is never
      true.  If the program will be interpreted by csh, you will need to
      replace "${1+"$@"}" with $*, even though that doesn't understand
      embedded spaces (and such) in the argument list.  To start up _s_h
      rather than _c_s_h, 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 _c_s_h, _s_h, 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 0; # ^ Run only under a shell

      If the filename supplied contains directory separators (and so 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.

      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.

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

      NNoottee:: TThhiiss iiss nnoott aa ssuubbssttiittuuttee ffoorr ""--TT""!! This is meant to be used
      _o_n_l_y 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".

      This has no effect if your perl was built without taint support.

 --TT   turns on "taint" so you can test them.  Ordinarily these checks are
      done only when running setuid or setgid.  It's a good idea to turn
      them on explicitly for programs that run on behalf of someone 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 construct.

 --uu   This 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 _u_n_d_u_m_p 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
      "CORE::dump()" function instead.  Note: availability of _u_n_d_u_m_p is
      platform specific and may not be available for a specific port of
      Perl.

 --UU   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 warnings must be enabled along with this
      option to actually _g_e_n_e_r_a_t_e the taint-check warnings.

 --vv   prints the version and patchlevel of your perl executable.

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

 --VV::_c_o_n_f_i_g_v_a_r
      Prints to STDOUT the value of the named configuration variable(s),
      with multiples when your "_c_o_n_f_i_g_v_a_r" argument looks like a regex
      (has non-letters).  For example:

          $ perl -V:libc
              libc='/lib/libc-2.2.4.so';
          $ perl -V:lib.
              libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
              libc='/lib/libc-2.2.4.so';
          $ perl -V:lib.*
              libpth='/usr/local/lib /lib /usr/lib';
              libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
              lib_ext='.a';
              libc='/lib/libc-2.2.4.so';
              libperl='libperl.a';
              ....

      Additionally, extra colons can be used to control formatting.  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`
          goodvfork=false;

      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

 --ww   prints warnings about dubious constructs, such as variable names
      mentioned only once and scalar variables used before being set;
      redefined subroutines; references to undefined filehandles;
      filehandles opened read-only that you are attempting to write on;
      values used as a number that don't _l_o_o_k like numbers; using an array
      as though it were a scalar; if your subroutines recurse more than
      100 deep; and innumerable other things.

      This switch really just enables the global $^W variable; normally,
      the lexically scoped "use warnings" pragma is preferred. 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 fine-grained warning facility is
      also available if you want to manipulate entire classes of warnings;
      see warnings.

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

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

      Forbidden in "PERL5OPT".

 --xx
 --xx_d_i_r_e_c_t_o_r_y
      tells Perl that the program is embedded in a larger chunk of
      unrelated text, such as in a mail message.  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.

      All references to line numbers by the program (warnings, errors,
      ...) will treat the "#!" line as the first line.  Thus a warning on
      the 2nd line of the program, which is on the 100th line in the file
      will be reported as line 2, not as line 100.  This can be overridden
      by using the "#line" directive.  (See "Plain Old Comments (Not!)" in
      perlsyn)

      If a directory name is specified, Perl will switch to that directory
      before running the program.  The --xx 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.

      The directory, if specified, must appear immediately following the
      --xx with no intervening whitespace.

EENNVVIIRROONNMMEENNTT #

 HOME        Used if "chdir" has no argument.

 LOGDIR      Used if "chdir" has no argument and "HOME" is not set.

 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.  Any architecture-
             specific and version-specific directories, such as
             _v_e_r_s_i_o_n_/_a_r_c_h_n_a_m_e_/, _v_e_r_s_i_o_n_/, or _a_r_c_h_n_a_m_e_/ under the specified
             locations are automatically included if they exist, with this
             lookup done at interpreter startup time.  In addition, any
             directories matching the entries in $Config{inc_version_list}
             are added.  (These typically would be for older compatible
             perl versions installed in the same directory tree.)

             If PERL5LIB is not defined, "PERLLIB" is used.  Directories
             are separated (like in PATH) by a colon on Unixish platforms
             and by a semicolon on Windows (the proper path separator
             being given by the command "perl -V:_p_a_t_h___s_e_p").

             When running taint checks, either because the program was
             running setuid or setgid, or the "-T" or "-t" switch was
             specified, neither PERL5LIB nor "PERLLIB" is consulted. The
             program should instead say:

                 use lib "/my/directory";

 PERL5OPT    Command-line options (switches).  Switches in this variable
             are treated as if they were on every Perl command line.  Only
             the --[[CCDDIIMMTTUUWWddmmttww]] switches are allowed.  When running taint
             checks (either because the program was running setuid or
             setgid, or because the "-T" or "-t" switch was used), this
             variable is ignored.  If PERL5OPT begins with --TT, tainting
             will be enabled and subsequent options ignored.  If PERL5OPT
             begins with --tt, tainting will be enabled, a writable dot
             removed from @INC, and subsequent options honored.

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

             It is conventional to start layer names with a colon (for
             example, ":perlio") to emphasize their similarity to variable
             "attributes". But the code that parses layer specification
             strings, which is also used to decode the PERLIO environment
             variable, treats the colon as a separator.

             An unset or empty PERLIO is equivalent to the default set of
             layers for your platform; for example, ":unix:perlio" on
             Unix-like systems and ":unix:crlf" on Windows and other DOS-
             like systems.

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

             Layers it makes sense to include in the PERLIO environment
             variable are briefly summarized below. For more details see
             PerlIO.

             :crlf   A layer which does CRLF to "\n" translation
                     distinguishing "text" and "binary" files in the
                     manner of MS-DOS and similar operating systems, and
                     also provides buffering similar to ":perlio" on these
                     architectures.

             :perlio This is a re-implementation of stdio-like buffering
                     written as a PerlIO layer.  As such it will call
                     whatever layer is below it for its operations,
                     typically ":unix".

             :stdio  This layer provides a PerlIO interface by wrapping
                     system's ANSI C "stdio" library calls. The layer
                     provides both buffering and IO. Note that the
                     ":stdio" layer does _n_o_t do CRLF translation even if
                     that is the platform's normal behaviour. You will
                     need a ":crlf" layer above it to do that.

             :unix   Low-level layer that calls "read", "write", "lseek",
                     etc.

             The default set of layers should give acceptable results on
             all platforms.

             For Unix platforms that will be the equivalent of
             ":unix:perlio" or ":stdio".  Configure is set up to prefer
             the ":stdio" implementation if the system's library provides
             for fast access to the buffer (not common on modern
             architectures); otherwise, it uses the ":unix:perlio"
             implementation.

             On Win32 the default in this release (5.30) is ":unix:crlf".
             Win32's ":stdio" has a number of bugs/mis-features for Perl
             IO which are somewhat depending on the version and vendor of
             the C compiler. Using our own ":crlf" layer as the buffer
             avoids those issues and makes things more uniform.

             This release (5.30) uses ":unix" as the bottom layer on
             Win32, and so still uses the C compiler's numeric file
             descriptor routines.

             The PERLIO environment variable is completely ignored when
             Perl is run in taint mode.

PERLIO_DEBUG #

             If set to the name of a file or device when Perl is run with
             the -Di command-line switch, the logging of certain
             operations of the PerlIO subsystem will be redirected to the
             specified file rather than going to stderr, which is the
             default. The file is opened in append mode. Typical uses are
             in Unix:

                % env PERLIO_DEBUG=/tmp/perlio.log perl -Di script ...

             and under Win32, the approximately equivalent:

                > set PERLIO_DEBUG=CON
                perl -Di script ...

             This functionality is disabled for setuid scripts, for
             scripts run with "-T", and for scripts run on a Perl built
             without "-DDEBUGGING" support.

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

             The PERLLIB environment variable is completely ignored when
             Perl is run in taint mode.

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

                     BEGIN { require "perl5db.pl" }

             The PERL5DB environment variable is only used when Perl is
             started with a bare "-d" switch.

PERL5DB_THREADED #

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

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

             Note that Perl doesn't use COMSPEC for this purpose because
             COMSPEC has a high degree of variability among users, leading
             to portability concerns.  Besides, Perl can use a shell that
             may not be fit for interactive use, and setting COMSPEC to
             such a shell may interfere with the proper functioning of
             other programs (which usually look in COMSPEC to find a shell
             fit for interactive use).

             Before Perl 5.10.0 and 5.8.8, PERL5SHELL was not taint
             checked when running external commands.  It is recommended
             that you explicitly set (or delete) $ENV{PERL5SHELL} when
             running in taint mode under Windows.

 PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
             Set to 1 to allow the use of non-IFS compatible LSPs (Layered
             Service Providers).  Perl normally searches for an IFS-
             compatible LSP because this is required for its emulation of
             Windows sockets as real filehandles.  However, this may cause
             problems if you have a firewall such as _M_c_A_f_e_e _G_u_a_r_d_i_a_n,
             which requires that all applications use its LSP but 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 _M_c_A_f_e_e _G_u_a_r_d_i_a_n happy--and in that particular
             case Perl still works too because _M_c_A_f_e_e _G_u_a_r_d_i_a_n's LSP
             actually plays other games which allow applications requiring
             IFS compatibility to work.

PERL_DEBUG_MSTATS #

             Relevant only if Perl is compiled with the "malloc" included
             with the Perl distribution; that is, if "perl -V:d_mymalloc"
             is "define".

             If set, this dumps out memory statistics after execution.  If
             set to an integer greater than one, also dumps out memory
             statistics after compilation.

PERL_DESTRUCT_LEVEL #

             Controls the behaviour of global destruction of objects and
             other references.  See "PERL_DESTRUCT_LEVEL" in perlhacktips
             for more information.

PERL_DL_NONLAZY #

             Set to "1" to have Perl resolve _a_l_l 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 them.

PERL_ENCODING #

             If using the "use encoding" pragma without an explicit
             encoding name, the PERL_ENCODING environment variable is
             consulted for an encoding name.

PERL_HASH_SEED #

             (Since Perl 5.8.1, new semantics in Perl 5.18.0)  Used to
             override the randomization of Perl's internal hash function.
             The value is expressed in hexadecimal, and may include a
             leading 0x. Truncated patterns are treated as though they are
             suffixed with sufficient 0's as required.

             If the option is provided, and "PERL_PERTURB_KEYS" is NOT
             set, then a value of '0' implies
             "PERL_PERTURB_KEYS=0"/"PERL_PERTURB_KEYS=NO" and any other
             value implies
             "PERL_PERTURB_KEYS=2"/"PERL_PERTURB_KEYS=DETERMINISTIC". See
             the documentation for PERL_PERTURB_KEYS for important caveats
             regarding the "DETERMINISTIC" mode.

             PPLLEEAASSEE NNOOTTEE:: TThhee hhaasshh sseeeedd iiss sseennssiittiivvee iinnffoorrmmaattiioonn. 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,
             "PERL_PERTURB_KEYS", and "PERL_HASH_SEED_DEBUG" for more
             information.

PERL_PERTURB_KEYS #

             (Since Perl 5.18.0)  Set to "0" or "NO" then traversing keys
             will be repeatable from run to run for the same
             "PERL_HASH_SEED".  Insertion into a hash will not change the
             order, except to provide for more space in the hash. When
             combined with setting PERL_HASH_SEED this mode is as close to
             pre 5.18 behavior as you can get.

             When set to "1" or "RANDOM" then traversing keys will be
             randomized.  Every time a hash is inserted into the key order
             will change in a random fashion. The order may not be
             repeatable in a following program run even if the
             PERL_HASH_SEED has been specified. This is the default mode
             for perl when no PERL_HASH_SEED has been explicitly provided.

             When set to "2" or "DETERMINISTIC" then inserting keys into a
             hash will cause the key order to change, but in a way that is
             repeatable from program run to program run, provided that the
             same hash seed is used, and that the code does not itself
             perform any non-deterministic operations and also provided
             exactly the same environment context.  Adding or removing an
             environment variable may and likely will change the key
             order. If any part of the code builds a hash using non-
             deterministic keys, for instance a hash keyed by the
             stringified form of a reference, or the address of the
             objects it contains, then this may and likely will have a
             global effect on the key order of *every* hash in the
             process. To work properly this setting MUST be coupled with
             the PERL_HASH_SEED to produce deterministic results, and in
             fact, if you do set the "PERL_HASH_SEED" explicitly you do
             not need to set this as well, it will be automatically set to
             this mode.

             NNOOTTEE:: Use of this option is considered insecure, and is
             intended only for debugging non-deterministic behavior in
             Perl's hash function. Do not use it in production.

             See "Algorithmic Complexity Attacks" in perlsec and
             "PERL_HASH_SEED" and "PERL_HASH_SEED_DEBUG" for more
             information. You can get and set the key traversal mask for a
             specific hash by using the "hash_traversal_mask()" function
             from Hash::Util.

PERL_HASH_SEED_DEBUG #

             (Since Perl 5.8.1.)  Set to "1" to display (to STDERR)
             information about the hash function, seed, and what type of
             key traversal randomization is in effect at the beginning of
             execution.  This, combined with "PERL_HASH_SEED" and
             "PERL_PERTURB_KEYS" is intended to aid in debugging
             nondeterministic behaviour caused by hash randomization.

             NNoottee that any information about the hash function, especially
             the hash seed is sseennssiittiivvee iinnffoorrmmaattiioonn: 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. DDoo nnoott ddiisscclloossee tthhee hhaasshh sseeeedd to people who
             don't need to know it. See also "hash_seed()" and
             "hash_traversal_mask()".

             An example output might be:

              HASH_FUNCTION = ONE_AT_A_TIME_HARD HASH_SEED = 0x652e9b9349a7a032 PERTURB_KEYS = 1 (RANDOM)

PERL_MEM_LOG #

             If your Perl was configured with --AAccccffllaaggss==--DDPPEERRLL__MMEEMM__LLOOGG,
             setting the environment variable "PERL_MEM_LOG" enables
             logging debug messages. The value has the form
             "<_n_u_m_b_e_r>[m][s][t]", where "_n_u_m_b_e_r" is the file descriptor
             number you want to write to (2 is default), and the
             combination of letters specifies that you want information
             about (m)emory and/or (s)v, optionally with (t)imestamps. For
             example, "PERL_MEM_LOG=1mst" logs all information to stdout.
             You can write to other opened file descriptors in a variety
             of ways:

               $ 3>foo3 PERL_MEM_LOG=3m perl ...

 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,
             PERL_ENV_TABLES, and SYS$TIMEZONE_DIFFERENTIAL, but are
             optional and discussed further in perlvms and in _R_E_A_D_M_E_._v_m_s
             in the Perl source distribution.

PERL_SIGNALS #

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

PERL_UNICODE #

             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 alternatively unset
             PERL_UNICODE in your shell before starting Perl).  See the
             description of the -C switch for more information.

PERL_USE_UNSAFE_INC #

             If perl has been configured to not have the current directory
             in @INC by default, this variable can be set to "1" to
             reinstate it.  It's primarily intended for use while building
             and testing modules that have not been updated to deal with
             "." not being in @INC and should not be set in the
             environment for day-to-day use.

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

PERL_INTERNAL_RAND_SEED #

             Set to a non-negative integer to seed the random number
             generator used internally by perl for a variety of purposes.

             Ignored if perl is run setuid or setgid.  Used only for some
             limited startup randomization (hash keys) if "-T" or "-t"
             perl is started with tainting enabled.

             Perl may be built to ignore this variable.

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

 Perl and its various modules and components, including its test
 frameworks, may sometimes make use of certain other environment
 variables.  Some of these are specific to a particular platform.  Please
 consult the appropriate module documentation and any documentation for
 your platform (like perlsolaris, perllinux, perlmacosx, perlwin32, etc)
 for variables peculiar to those specific situations.

 Perl makes all environment variables available to the program being
 executed, and passes these along to any child processes it starts.
 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)};

OORRDDEERR OOFF AAPPPPLLIICCAATTIIOONN #

 Some options, in particular "-I", "-M", "PERL5LIB" and "PERL5OPT" can
 interact, and the order in which they are applied is important.

 Note that this section does not document what _a_c_t_u_a_l_l_y happens inside the
 perl interpreter, it documents what _e_f_f_e_c_t_i_v_e_l_y happens.

 -I  The effect of multiple "-I" options is to "unshift" them onto @INC
     from right to left. So for example:

         perl -I 1 -I 2 -I 3

     will first prepend 3 onto the front of @INC, then prepend 2, and then
     prepend 1. The result is that @INC begins with:

         qw(1 2 3)

 -M  Multiple "-M" options are processed from left to right. So this:

         perl -Mlib=1 -Mlib=2 -Mlib=3

     will first use the lib pragma to prepend 1 to @INC, then it will
     prepend 2, then it will prepend 3, resulting in an @INC that begins
     with:

         qw(3 2 1)

 the PERL5LIB environment variable
     This contains a list of directories, separated by colons. The entire
     list is prepended to @INC in one go. This:

         PERL5LIB=1:2:3 perl

     will result in an @INC that begins with:

         qw(1 2 3)

 combinations of -I, -M and PERL5LIB
     "PERL5LIB" is applied first, then all the "-I" arguments, then all
     the "-M" arguments. This:

         PERL5LIB=e1:e2 perl -I i1 -Mlib=m1 -I i2 -Mlib=m2

     will result in an @INC that begins with:

         qw(m2 m1 i1 i2 e1 e2)

 the PERL5OPT environment variable
     This contains a space separated list of switches. We only consider
     the effects of "-M" and "-I" in this section.

     After normal processing of "-I" switches from the command line, all
     the "-I" switches in "PERL5OPT" are extracted. They are processed
     from left to right instead of from right to left. Also note that
     while whitespace is allowed between a "-I" and its directory on the
     command line, it is not allowed in "PERL5OPT".

     After normal processing of "-M" switches from the command line, all
     the "-M" switches in "PERL5OPT" are extracted. They are processed
     from left to right, _i_._e_. the same as those on the command line.

     An example may make this clearer:

         export PERL5OPT="-Mlib=optm1 -Iopti1 -Mlib=optm2 -Iopti2"
         export PERL5LIB=e1:e2
         perl -I i1 -Mlib=m1 -I i2 -Mlib=m2

     will result in an @INC that begins with:

         qw(
             optm2
             optm1

             m2
             m1

             opti2
             opti1

             i1
             i2

             e1
             e2
         )

 Other complications
     There are some complications that are ignored in the examples above:

     arch and version subdirs
         All of "-I", "PERL5LIB" and "use lib" will also prepend arch and
         version subdirs if they are present

     sitecustomize.pl

perl v5.36.3 2023-02-15 PERLRUN(1)