3 perlrun - how to execute the Perl interpreter
7 B<perl> S<[ B<-sTtuUWX> ]>
8 S<[ B<-hv> ] [ B<-V>[:I<configvar>] ]>
9 S<[ B<-cw> ] [ B<-d>[B<t>][:I<debugger>] ] [ B<-D>[I<number/list>] ]>
10 S<[ B<-pna> ] [ B<-F>I<pattern> ] [ B<-l>[I<octal>] ] [ B<-0>[I<octal/hexadecimal>] ]>
11 S<[ B<-I>I<dir> ] [ B<-m>[B<->]I<module> ] [ B<-M>[B<->]I<'module...'> ] [ B<-f> ]>
12 S<[ B<-C [I<number/list>] >]>
15 S<[ B<-i>[I<extension>] ]>
16 S<[ [B<-e>|B<-E>] I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...>
20 The normal way to run a Perl program is by making it directly
21 executable, or else by passing the name of the source file as an
22 argument on the command line. (An interactive Perl environment
23 is also possible--see L<perldebug> for details on how to do that.)
24 Upon startup, Perl looks for your program in one of the following
31 Specified line by line via B<-e> or B<-E> switches on the command line.
35 Contained in the file specified by the first filename on the command line.
36 (Note that systems supporting the C<#!> notation invoke interpreters this
37 way. See L</Location of Perl>.)
41 Passed in implicitly via standard input. This works only if there are
42 no filename arguments--to pass arguments to a STDIN-read program you
43 must explicitly specify a "-" for the program name.
47 With methods 2 and 3, Perl starts parsing the input file from the
48 beginning, unless you've specified a B<-x> switch, in which case it
49 scans for the first line starting with C<#!> and containing the word
50 "perl", and starts there instead. This is useful for running a program
51 embedded in a larger message. (In this case you would indicate the end
52 of the program using the C<__END__> token.)
54 The C<#!> line is always examined for switches as the line is being
55 parsed. Thus, if you're on a machine that allows only one argument
56 with the C<#!> line, or worse, doesn't even recognize the C<#!> line, you
57 still can get consistent switch behaviour regardless of how Perl was
58 invoked, even if B<-x> was used to find the beginning of the program.
60 Because historically some operating systems silently chopped off
61 kernel interpretation of the C<#!> line after 32 characters, some
62 switches may be passed in on the command line, and some may not;
63 you could even get a "-" without its letter, if you're not careful.
64 You probably want to make sure that all your switches fall either
65 before or after that 32-character boundary. Most switches don't
66 actually care if they're processed redundantly, but getting a "-"
67 instead of a complete switch could cause Perl to try to execute
68 standard input instead of your program. And a partial B<-I> switch
69 could also cause odd results.
71 Some switches do care if they are processed twice, for instance
72 combinations of B<-l> and B<-0>. Either put all the switches after
73 the 32-character boundary (if applicable), or replace the use of
74 B<-0>I<digits> by C<BEGIN{ $/ = "\0digits"; }>.
76 Parsing of the C<#!> switches starts wherever "perl" is mentioned in the line.
77 The sequences "-*" and "- " are specifically ignored so that you could,
78 if you were so inclined, say
82 eval 'exec perl -x -wS $0 ${1+"$@"}'
85 to let Perl see the B<-p> switch.
87 A similar trick involves the I<env> program, if you have it.
91 The examples above use a relative path to the perl interpreter,
92 getting whatever version is first in the user's path. If you want
93 a specific version of Perl, say, perl5.14.1, you should place
94 that directly in the C<#!> line's path.
96 If the C<#!> line does not contain the word "perl" nor the word "indir",
97 the program named after the C<#!> is executed instead of the Perl
98 interpreter. This is slightly bizarre, but it helps people on machines
99 that don't do C<#!>, because they can tell a program that their SHELL is
100 F</usr/bin/perl>, and Perl will then dispatch the program to the correct
101 interpreter for them.
103 After locating your program, Perl compiles the entire program to an
104 internal form. If there are any compilation errors, execution of the
105 program is not attempted. (This is unlike the typical shell script,
106 which might run part-way through before finding a syntax error.)
108 If the program is syntactically correct, it is executed. If the program
109 runs off the end without hitting an exit() or die() operator, an implicit
110 C<exit(0)> is provided to indicate successful completion.
112 =head2 #! and quoting on non-Unix systems
115 Unix's C<#!> technique can be simulated on other systems:
123 extproc perl -S -your_switches
125 as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's
130 Create a batch file to run your program, and codify it in
131 C<ALTERNATE_SHEBANG> (see the F<dosish.h> file in the source
132 distribution for more information).
136 The Win95/NT installation, when using the ActiveState installer for Perl,
137 will modify the Registry to associate the F<.pl> extension with the perl
138 interpreter. If you install Perl by other means (including building from
139 the sources), you may have to modify the Registry yourself. Note that
140 this means you can no longer tell the difference between an executable
141 Perl program and a Perl library file.
147 $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
148 $ exit++ + ++$status != 0 and $exit = $status = undef;
150 at the top of your program, where B<-mysw> are any command line switches you
151 want to pass to Perl. You can now invoke the program directly, by saying
152 C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly
153 via F<DCL$PATH> by just using the name of the program).
155 This incantation is a bit much to remember, but Perl will display it for
156 you if you say C<perl "-V:startperl">.
160 Command-interpreters on non-Unix systems have rather different ideas
161 on quoting than Unix shells. You'll need to learn the special
162 characters in your command-interpreter (C<*>, C<\> and C<"> are
163 common) and how to protect whitespace and these characters to run
164 one-liners (see L<-e|/-e commandline> below).
166 On some systems, you may have to change single-quotes to double ones,
167 which you must I<not> do on Unix or Plan 9 systems. You might also
168 have to change a single % to a %%.
173 perl -e 'print "Hello world\n"'
176 perl -e "print \"Hello world\n\""
179 perl -e "print ""Hello world\n"""
181 The problem is that none of this is reliable: it depends on the
182 command and it is entirely possible neither works. If I<4DOS> were
183 the command shell, this would probably work better:
185 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
187 B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in
188 when nobody was looking, but just try to find documentation for its
191 There is no general solution to all of this. It's just a mess.
193 =head2 Location of Perl
194 X<perl, location of interpreter>
196 It may seem obvious to say, but Perl is useful only when users can
197 easily find it. When possible, it's good for both F</usr/bin/perl>
198 and F</usr/local/bin/perl> to be symlinks to the actual binary. If
199 that can't be done, system administrators are strongly encouraged
200 to put (symlinks to) perl and its accompanying utilities into a
201 directory typically found along a user's PATH, or in some other
202 obvious and convenient place.
204 In this documentation, C<#!/usr/bin/perl> on the first line of the program
205 will stand in for whatever method works on your system. You are
206 advised to use a specific path if you care about a specific version.
208 #!/usr/local/bin/perl5.14
210 or if you just want to be running at least version, place a statement
211 like this at the top of your program:
215 =head2 Command Switches
216 X<perl, command switches> X<command switches>
218 As with all standard commands, a single-character switch may be
219 clustered with the following switch, if any.
221 #!/usr/bin/perl -spi.orig # same as -s -p -i.orig
223 A C<--> signals the end of options and disables further option processing. Any
224 arguments after the C<--> are treated as filenames and arguments.
230 =item B<-0>[I<octal/hexadecimal>]
233 specifies the input record separator (C<$/>) as an octal or
234 hexadecimal number. If there are no digits, the null character is the
235 separator. Other switches may precede or follow the digits. For
236 example, if you have a version of I<find> which can print filenames
237 terminated by the null character, you can say this:
239 find . -name '*.orig' -print0 | perl -n0e unlink
241 The special value 00 will cause Perl to slurp files in paragraph mode.
242 Any value 0400 or above will cause Perl to slurp files whole, but by convention
243 the value 0777 is the one normally used for this purpose.
245 You can also specify the separator character using hexadecimal notation:
246 B<-0xI<HHH...>>, where the C<I<H>> are valid hexadecimal digits. Unlike
247 the octal form, this one may be used to specify any Unicode character, even
248 those beyond 0xFF. So if you I<really> want a record separator of 0777,
249 specify it as B<-0x1FF>. (This means that you cannot use the B<-x> option
250 with a directory name that consists of hexadecimal digits, or else Perl
251 will think you have specified a hex number to B<-0>.)
256 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
257 split command to the @F array is done as the first thing inside the
258 implicit while loop produced by the B<-n> or B<-p>.
260 perl -ane 'print pop(@F), "\n";'
269 An alternate delimiter may be specified using B<-F>.
271 B<-a> implicitly sets B<-n>.
273 =item B<-C [I<number/list>]>
276 The B<-C> flag controls some of the Perl Unicode features.
278 As of 5.8.1, the B<-C> can be followed either by a number or a list
279 of option letters. The letters, their numeric values, and effects
280 are as follows; listing the letters is equal to summing the numbers.
282 I 1 STDIN is assumed to be in UTF-8
283 O 2 STDOUT will be in UTF-8
284 E 4 STDERR will be in UTF-8
286 i 8 UTF-8 is the default PerlIO layer for input streams
287 o 16 UTF-8 is the default PerlIO layer for output streams
289 A 32 the @ARGV elements are expected to be strings encoded
291 L 64 normally the "IOEioA" are unconditional, the L makes
292 them conditional on the locale environment variables
293 (the LC_ALL, LC_CTYPE, and LANG, in the order of
294 decreasing precedence) -- if the variables indicate
295 UTF-8, then the selected "IOEioA" are in effect
296 a 256 Set ${^UTF8CACHE} to -1, to run the UTF-8 caching
297 code in debugging mode.
299 =for documenting_the_underdocumented
300 perl.h gives W/128 as PERL_UNICODE_WIDESYSCALLS "/* for Sarathy */"
303 perltodo mentions Unicode in %ENV and filenames. I guess that these will be
304 options e and f (or F).
306 For example, B<-COE> and B<-C6> will both turn on UTF-8-ness on both
307 STDOUT and STDERR. Repeating letters is just redundant, not cumulative
310 The C<io> options mean that any subsequent open() (or similar I/O
311 operations) in the current file scope will have the C<:utf8> PerlIO layer
312 implicitly applied to them, in other words, UTF-8 is expected from any
313 input stream, and UTF-8 is produced to any output stream. This is just
314 the default, with explicit layers in open() and with binmode() one can
315 manipulate streams as usual.
317 B<-C> on its own (not followed by any number or option list), or the
318 empty string C<""> for the C<PERL_UNICODE> environment variable, has the
319 same effect as B<-CSDL>. In other words, the standard I/O handles and
320 the default C<open()> layer are UTF-8-fied I<but> only if the locale
321 environment variables indicate a UTF-8 locale. This behaviour follows
322 the I<implicit> (and problematic) UTF-8 behaviour of Perl 5.8.0.
323 (See L<perl581delta/UTF-8 no longer default under UTF-8 locales>.)
325 You can use B<-C0> (or C<"0"> for C<PERL_UNICODE>) to explicitly
326 disable all the above Unicode features.
328 The read-only magic variable C<${^UNICODE}> reflects the numeric value
329 of this setting. This variable is set during Perl startup and is
330 thereafter read-only. If you want runtime effects, use the three-arg
331 open() (see L<perlfunc/open>), the two-arg binmode() (see L<perlfunc/binmode>),
332 and the C<open> pragma (see L<open>).
334 (In Perls earlier than 5.8.1 the B<-C> switch was a Win32-only switch
335 that enabled the use of Unicode-aware "wide system call" Win32 APIs.
336 This feature was practically unused, however, and the command line
337 switch was therefore "recycled".)
339 B<Note:> Since perl 5.10.1, if the B<-C> option is used on the C<#!> line,
340 it must be specified on the command line as well, since the standard streams
341 are already set up at this point in the execution of the perl interpreter.
342 You can also use binmode() to set the encoding of an I/O stream.
347 causes Perl to check the syntax of the program and then exit without
348 executing it. Actually, it I<will> execute any C<BEGIN>, C<UNITCHECK>,
349 or C<CHECK> blocks and any C<use> statements: these are considered as
350 occurring outside the execution of your program. C<INIT> and C<END>
351 blocks, however, will be skipped.
358 runs the program under the Perl debugger. See L<perldebug>.
359 If B<t> is specified, it indicates to the debugger that threads
360 will be used in the code being debugged.
362 =item B<-d:>I<MOD[=bar,baz]>
365 =item B<-dt:>I<MOD[=bar,baz]>
367 runs the program under the control of a debugging, profiling, or tracing
368 module installed as C<Devel::I<MOD>>. E.g., B<-d:DProf> executes the
369 program using the C<Devel::DProf> profiler. As with the B<-M> flag, options
370 may be passed to the C<Devel::I<MOD>> package where they will be received
371 and interpreted by the C<Devel::I<MOD>::import> routine. Again, like B<-M>,
372 use -B<-d:-I<MOD>> to call C<Devel::I<MOD>::unimport> instead of import. The
373 comma-separated list of options must follow a C<=> character. If B<t> is
374 specified, it indicates to the debugger that threads will be used in the
375 code being debugged. See L<perldebug>.
377 =item B<-D>I<letters>
378 X<-D> X<DEBUGGING> X<-DDEBUGGING>
382 sets debugging flags. This switch is enabled only if your perl binary has
383 been built with debugging enabled: normal production perls won't have
386 For example, to watch how perl executes your program, use B<-Dtls>.
387 Another nice value is B<-Dx>, which lists your compiled syntax tree, and
388 B<-Dr> displays compiled regular expressions; the format of the output is
389 explained in L<perldebguts>.
391 As an alternative, specify a number instead of list of letters (e.g.,
392 B<-D14> is equivalent to B<-Dtls>):
394 1 p Tokenizing and parsing (with v, displays parse
396 2 s Stack snapshots (with v, displays all stacks)
397 4 l Context (loop) stack processing
399 16 o Method and overloading resolution
400 32 c String/numeric conversions
401 64 P Print profiling info, source file input state
402 128 m Memory and SV allocation
403 256 f Format processing
404 512 r Regular expression parsing and execution
405 1024 x Syntax tree dump
406 2048 u Tainting checks
407 4096 U Unofficial, User hacking (reserved for private,
409 16384 X Scratchpad allocation
411 65536 S Op slab allocation
413 262144 R Include reference counts of dumped variables
415 524288 J show s,t,P-debug (don't Jump over) on opcodes within
417 1048576 v Verbose: use in conjunction with other flags to
418 increase the verbosity of the output. Is a no-op on
419 many of the other flags
420 2097152 C Copy On Write
421 4194304 A Consistency checks on internal structures
422 8388608 q quiet - currently only suppresses the "EXECUTING"
424 16777216 M trace smart match resolution
425 33554432 B dump suBroutine definitions, including special
427 67108864 L trace Locale-related info; what gets output is very
429 134217728 i trace PerlIO layer processing. Set PERLIO_DEBUG to
430 the filename to trace to.
432 All these flags require B<-DDEBUGGING> when you compile the Perl
433 executable (but see C<:opd> in L<Devel::Peek> or L<re/'debug' mode>
434 which may change this).
435 See the F<INSTALL> file in the Perl source distribution
438 If you're just trying to get a print out of each line of Perl code
439 as it executes, the way that C<sh -x> provides for shell scripts,
440 you can't use Perl's B<-D> switch. Instead do this
442 # If you have "env" utility
443 env PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
445 # Bourne shell syntax
446 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
449 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
451 See L<perldebug> for details and variations.
453 =item B<-e> I<commandline>
456 may be used to enter one line of program. If B<-e> is given, Perl
457 will not look for a filename in the argument list. Multiple B<-e>
458 commands may be given to build up a multi-line script. Make sure
459 to use semicolons where you would in a normal program.
461 =item B<-E> I<commandline>
464 behaves just like B<-e>, except that it implicitly enables all
465 optional features (in the main compilation unit). See L<feature>.
468 X<-f> X<sitecustomize> X<sitecustomize.pl>
470 Disable executing F<$Config{sitelib}/sitecustomize.pl> at startup.
472 Perl can be built so that it by default will try to execute
473 F<$Config{sitelib}/sitecustomize.pl> at startup (in a BEGIN block).
474 This is a hook that allows the sysadmin to customize how Perl behaves.
475 It can for instance be used to add entries to the @INC array to make Perl
476 find modules in non-standard locations.
478 Perl actually inserts the following code:
481 do { local $!; -f "$Config{sitelib}/sitecustomize.pl"; }
482 && do "$Config{sitelib}/sitecustomize.pl";
485 Since it is an actual C<do> (not a C<require>), F<sitecustomize.pl>
486 doesn't need to return a true value. The code is run in package C<main>,
487 in its own lexical scope. However, if the script dies, C<$@> will not
490 The value of C<$Config{sitelib}> is also determined in C code and not
491 read from C<Config.pm>, which is not loaded.
493 The code is executed I<very> early. For example, any changes made to
494 C<@INC> will show up in the output of `perl -V`. Of course, C<END>
495 blocks will be likewise executed very late.
497 To determine at runtime if this capability has been compiled in your
498 perl, you can check the value of C<$Config{usesitecustomize}>.
500 =item B<-F>I<pattern>
503 specifies the pattern to split on for B<-a>. The pattern may be
504 surrounded by C<//>, C<"">, or C<''>, otherwise it will be put in single
505 quotes. You can't use literal whitespace or NUL characters in the pattern.
507 B<-F> implicitly sets both B<-a> and B<-n>.
512 prints a summary of the options.
514 =item B<-i>[I<extension>]
517 specifies that files processed by the C<E<lt>E<gt>> construct are to be
518 edited in-place. It does this by renaming the input file, opening the
519 output file by the original name, and selecting that output file as the
520 default for print() statements. The extension, if supplied, is used to
521 modify the name of the old file to make a backup copy, following these
524 If no extension is supplied, and your system supports it, the original
525 I<file> is kept open without a name while the output is redirected to
526 a new file with the original I<filename>. When perl exits, cleanly or not,
527 the original I<file> is unlinked.
529 If the extension doesn't contain a C<*>, then it is appended to the
530 end of the current filename as a suffix. If the extension does
531 contain one or more C<*> characters, then each C<*> is replaced
532 with the current filename. In Perl terms, you could think of this
535 ($backup = $extension) =~ s/\*/$file_name/g;
537 This allows you to add a prefix to the backup file, instead of (or in
538 addition to) a suffix:
540 $ perl -pi'orig_*' -e 's/bar/baz/' fileA # backup to
543 Or even to place backup copies of the original files into another
544 directory (provided the directory already exists):
546 $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to
549 These sets of one-liners are equivalent:
551 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
552 $ perl -pi'*' -e 's/bar/baz/' fileA # overwrite current file
554 $ perl -pi'.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
555 $ perl -pi'*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
557 From the shell, saying
559 $ perl -p -i.orig -e "s/foo/bar/; ... "
561 is the same as using the program:
563 #!/usr/bin/perl -pi.orig
566 which is equivalent to
569 $extension = '.orig';
571 if ($ARGV ne $oldargv) {
572 if ($extension !~ /\*/) {
573 $backup = $ARGV . $extension;
576 ($backup = $extension) =~ s/\*/$ARGV/g;
578 rename($ARGV, $backup);
579 open(ARGVOUT, ">$ARGV");
586 print; # this prints to original filename
590 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
591 know when the filename has changed. It does, however, use ARGVOUT for
592 the selected filehandle. Note that STDOUT is restored as the default
593 output filehandle after the loop.
595 As shown above, Perl creates the backup file whether or not any output
596 is actually changed. So this is just a fancy way to copy files:
598 $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
600 $ perl -p -i'.orig' -e 1 file1 file2 file3...
602 You can use C<eof> without parentheses to locate the end of each input
603 file, in case you want to append to each file, or reset line numbering
604 (see example in L<perlfunc/eof>).
606 If, for a given file, Perl is unable to create the backup file as
607 specified in the extension then it will skip that file and continue on
608 with the next one (if it exists).
610 For a discussion of issues surrounding file permissions and B<-i>, see
611 L<perlfaq5/Why does Perl let me delete read-only files? Why does -i clobber
612 protected files? Isn't this a bug in Perl?>.
614 You cannot use B<-i> to create directories or to strip extensions from
617 Perl does not expand C<~> in filenames, which is good, since some
618 folks use it for their backup files:
620 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
622 Note that because B<-i> renames or deletes the original file before
623 creating a new file of the same name, Unix-style soft and hard links will
626 Finally, the B<-i> switch does not impede execution when no
627 files are given on the command line. In this case, no backup is made
628 (the original file cannot, of course, be determined) and processing
629 proceeds from STDIN to STDOUT as might be expected.
631 =item B<-I>I<directory>
634 Directories specified by B<-I> are prepended to the search path for
637 =item B<-l>[I<octnum>]
640 enables automatic line-ending processing. It has two separate
641 effects. First, it automatically chomps C<$/> (the input record
642 separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
643 (the output record separator) to have the value of I<octnum> so
644 that any print statements will have that separator added back on.
645 If I<octnum> is omitted, sets C<$\> to the current value of
646 C<$/>. For instance, to trim lines to 80 columns:
648 perl -lpe 'substr($_, 80) = ""'
650 Note that the assignment C<$\ = $/> is done when the switch is processed,
651 so the input record separator can be different than the output record
652 separator if the B<-l> switch is followed by a B<-0> switch:
654 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
656 This sets C<$\> to newline and then sets C<$/> to the null character.
658 =item B<-m>[B<->]I<module>
661 =item B<-M>[B<->]I<module>
663 =item B<-M>[B<->]I<'module ...'>
665 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
667 B<-m>I<module> executes C<use> I<module> C<();> before executing your
668 program. This loads the module, but does not call its C<import> method,
669 so does not import subroutines and does not give effect to a pragma.
671 B<-M>I<module> executes C<use> I<module> C<;> before executing your
672 program. This loads the module and calls its C<import> method, causing
673 the module to have its default effect, typically importing subroutines
674 or giving effect to a pragma.
675 You can use quotes to add extra code after the module name,
676 e.g., C<'-MI<MODULE> qw(foo bar)'>.
678 If the first character after the B<-M> or B<-m> is a dash (B<->)
679 then the 'use' is replaced with 'no'.
680 This makes no difference for B<-m>.
682 A little builtin syntactic sugar means you can also say
683 B<-mI<MODULE>=foo,bar> or B<-MI<MODULE>=foo,bar> as a shortcut for
684 B<'-MI<MODULE> qw(foo bar)'>. This avoids the need to use quotes when
685 importing symbols. The actual code generated by B<-MI<MODULE>=foo,bar> is
686 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
687 removes the distinction between B<-m> and B<-M>; that is,
688 B<-mI<MODULE>=foo,bar> is the same as B<-MI<MODULE>=foo,bar>.
690 A consequence of the C<split> formulation
691 is that B<-MI<MODULE>=number> never does a version check,
692 unless C<I<MODULE>::import()> itself is set up to do a version check, which
693 could happen for example if I<MODULE> inherits from L<Exporter>.
698 causes Perl to assume the following loop around your program, which
699 makes it iterate over filename arguments somewhat like I<sed -n> or
704 ... # your program goes here
707 Note that the lines are not printed by default. See L</-p> to have
708 lines printed. If a file named by an argument cannot be opened for
709 some reason, Perl warns you about it and moves on to the next file.
711 Also note that C<< <> >> passes command line arguments to
712 L<perlfunc/open>, which doesn't necessarily interpret them as file names.
713 See L<perlop> for possible security implications.
715 Here is an efficient way to delete all files that haven't been modified for
718 find . -mtime +7 -print | perl -nle unlink
720 This is faster than using the B<-exec> switch of I<find> because you don't
721 have to start a process on every filename found (but it's not faster
722 than using the B<-delete> switch available in newer versions of I<find>.
723 It does suffer from the bug of mishandling newlines in pathnames, which
724 you can fix if you follow the example under B<-0>.
726 C<BEGIN> and C<END> blocks may be used to capture control before or after
727 the implicit program loop, just as in I<awk>.
732 causes Perl to assume the following loop around your program, which
733 makes it iterate over filename arguments somewhat like I<sed>:
738 ... # your program goes here
740 print or die "-p destination: $!\n";
743 If a file named by an argument cannot be opened for some reason, Perl
744 warns you about it, and moves on to the next file. Note that the
745 lines are printed automatically. An error occurring during printing is
746 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
747 overrides a B<-n> switch.
749 C<BEGIN> and C<END> blocks may be used to capture control before or after
750 the implicit loop, just as in I<awk>.
755 enables rudimentary switch parsing for switches on the command
756 line after the program name but before any filename arguments (or before
757 an argument of B<-->). Any switch found there is removed from @ARGV and sets the
758 corresponding variable in the Perl program. The following program
759 prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
760 if it is invoked with B<-xyz=abc>.
763 if ($xyz) { print "$xyz\n" }
765 Do note that a switch like B<--help> creates the variable C<${-help}>, which is
766 not compliant with C<use strict "refs">. Also, when using this option on a
767 script with warnings enabled you may get a lot of spurious "used only once"
773 makes Perl use the PATH environment variable to search for the
774 program unless the name of the program contains path separators.
776 On some platforms, this also makes Perl append suffixes to the
777 filename while searching for it. For example, on Win32 platforms,
778 the ".bat" and ".cmd" suffixes are appended if a lookup for the
779 original name fails, and if the name does not already end in one
780 of those suffixes. If your Perl was compiled with C<DEBUGGING> turned
781 on, using the B<-Dp> switch to Perl shows how the search progresses.
783 Typically this is used to emulate C<#!> startup on platforms that don't
784 support C<#!>. It's also convenient when debugging a script that uses C<#!>,
785 and is thus normally found by the shell's $PATH search mechanism.
787 This example works on many platforms that have a shell compatible with
791 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
792 if $running_under_some_shell;
794 The system ignores the first line and feeds the program to F</bin/sh>,
795 which proceeds to try to execute the Perl program as a shell script.
796 The shell executes the second line as a normal shell command, and thus
797 starts up the Perl interpreter. On some systems $0 doesn't always
798 contain the full pathname, so the B<-S> tells Perl to search for the
799 program if necessary. After Perl locates the program, it parses the
800 lines and ignores them because the variable $running_under_some_shell
801 is never true. If the program will be interpreted by csh, you will need
802 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
803 embedded spaces (and such) in the argument list. To start up I<sh> rather
804 than I<csh>, some systems may have to replace the C<#!> line with a line
805 containing just a colon, which will be politely ignored by Perl. Other
806 systems can't control that, and need a totally devious construct that
807 will work under any of I<csh>, I<sh>, or Perl, such as the following:
809 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
810 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
811 if $running_under_some_shell;
813 If the filename supplied contains directory separators (and so is an
814 absolute or relative pathname), and if that file is not found,
815 platforms that append file extensions will do so and try to look
816 for the file with those extensions added, one by one.
818 On DOS-like platforms, if the program does not contain directory
819 separators, it will first be searched for in the current directory
820 before being searched for on the PATH. On Unix platforms, the
821 program will be searched for strictly on the PATH.
826 Like B<-T>, but taint checks will issue warnings rather than fatal
827 errors. These warnings can now be controlled normally with C<no warnings
830 B<Note: This is not a substitute for C<-T>!> This is meant to be
831 used I<only> as a temporary development aid while securing legacy code:
832 for real production code and for new secure code written from scratch,
833 always use the real B<-T>.
838 turns on "taint" so you can test them. Ordinarily
839 these checks are done only when running setuid or setgid. It's a
840 good idea to turn them on explicitly for programs that run on behalf
841 of someone else whom you might not necessarily trust, such as CGI
842 programs or any internet servers you might write in Perl. See
843 L<perlsec> for details. For security reasons, this option must be
844 seen by Perl quite early; usually this means it must appear early
845 on the command line or in the C<#!> line for systems which support
851 This switch causes Perl to dump core after compiling your
852 program. You can then in theory take this core dump and turn it
853 into an executable file by using the I<undump> program (not supplied).
854 This speeds startup at the expense of some disk space (which you
855 can minimize by stripping the executable). (Still, a "hello world"
856 executable comes out to about 200K on my machine.) If you want to
857 execute a portion of your program before dumping, use the C<CORE::dump()>
858 function instead. Note: availability of I<undump> is platform
859 specific and may not be available for a specific port of Perl.
864 allows Perl to do unsafe operations. Currently the only "unsafe"
865 operations are attempting to unlink directories while running as superuser
866 and running setuid programs with fatal taint checks turned into warnings.
867 Note that warnings must be enabled along with this option to actually
868 I<generate> the taint-check warnings.
873 prints the version and patchlevel of your perl executable.
878 prints summary of the major perl configuration values and the current
881 =item B<-V:>I<configvar>
883 Prints to STDOUT the value of the named configuration variable(s),
884 with multiples when your C<I<configvar>> argument looks like a regex (has
885 non-letters). For example:
888 libc='/lib/libc-2.2.4.so';
890 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
891 libc='/lib/libc-2.2.4.so';
893 libpth='/usr/local/lib /lib /usr/lib';
894 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
896 libc='/lib/libc-2.2.4.so';
900 Additionally, extra colons can be used to control formatting. A
901 trailing colon suppresses the linefeed and terminator ";", allowing
902 you to embed queries into shell commands. (mnemonic: PATH separator
905 $ echo "compression-vars: " `perl -V:z.*: ` " are here !"
906 compression-vars: zcat='' zip='zip' are here !
908 A leading colon removes the "name=" part of the response, this allows
909 you to map to the name you need. (mnemonic: empty label)
911 $ echo "goodvfork="`./perl -Ilib -V::usevfork`
914 Leading and trailing colons can be used together if you need
915 positional parameter values without the names. Note that in the case
916 below, the C<PERL_API> params are returned in alphabetical order.
918 $ echo building_on `perl -V::osname: -V::PERL_API_.*:` now
919 building_on 'linux' '5' '1' '9' now
924 prints warnings about dubious constructs, such as variable names
925 mentioned only once and scalar variables used
926 before being set; redefined subroutines; references to undefined
927 filehandles; filehandles opened read-only that you are attempting
928 to write on; values used as a number that don't I<look> like numbers;
929 using an array as though it were a scalar; if your subroutines
930 recurse more than 100 deep; and innumerable other things.
932 This switch really just enables the global C<$^W> variable; normally,
933 the lexically scoped C<use warnings> pragma is preferred. You
934 can disable or promote into fatal errors specific warnings using
935 C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
936 See also L<perldiag> and L<perltrap>. A fine-grained warning
937 facility is also available if you want to manipulate entire classes
938 of warnings; see L<warnings>.
943 Enables all warnings regardless of C<no warnings> or C<$^W>.
949 Disables all warnings regardless of C<use warnings> or C<$^W>.
955 =item B<-x>I<directory>
957 tells Perl that the program is embedded in a larger chunk of unrelated
958 text, such as in a mail message. Leading garbage will be
959 discarded until the first line that starts with C<#!> and contains the
960 string "perl". Any meaningful switches on that line will be applied.
962 All references to line numbers by the program (warnings, errors, ...)
963 will treat the C<#!> line as the first line.
964 Thus a warning on the 2nd line of the program, which is on the 100th
965 line in the file will be reported as line 2, not as line 100.
966 This can be overridden by using the C<#line> directive.
967 (See L<perlsyn/"Plain Old Comments (Not!)">)
969 If a directory name is specified, Perl will switch to that directory
970 before running the program. The B<-x> switch controls only the
971 disposal of leading garbage. The program must be terminated with
972 C<__END__> if there is trailing garbage to be ignored; the program
973 can process any or all of the trailing garbage via the C<DATA> filehandle
976 The directory, if specified, must appear immediately following the B<-x>
977 with no intervening whitespace.
982 X<perl, environment variables>
989 Used if C<chdir> has no argument.
994 Used if C<chdir> has no argument and HOME is not set.
999 Used in executing subprocesses, and in finding the program if B<-S> is
1005 A list of directories in which to look for Perl library files before
1006 looking in the standard library.
1007 Any architecture-specific and version-specific directories,
1008 such as F<version/archname/>, F<version/>, or F<archname/> under the
1009 specified locations are automatically included if they exist, with this
1010 lookup done at interpreter startup time. In addition, any directories
1011 matching the entries in C<$Config{inc_version_list}> are added.
1012 (These typically would be for older compatible perl versions installed
1013 in the same directory tree.)
1015 If PERL5LIB is not defined, PERLLIB is used. Directories are separated
1016 (like in PATH) by a colon on Unixish platforms and by a semicolon on
1017 Windows (the proper path separator being given by the command C<perl
1020 When running taint checks, either because the program was running setuid or
1021 setgid, or the B<-T> or B<-t> switch was specified, neither PERL5LIB nor
1022 PERLLIB is consulted. The program should instead say:
1024 use lib "/my/directory";
1029 Command-line options (switches). Switches in this variable are treated
1030 as if they were on every Perl command line. Only the B<-[CDIMTUWdmtw]>
1031 switches are allowed. When running taint checks (either because the
1032 program was running setuid or setgid, or because the B<-T> or B<-t>
1033 switch was used), this variable is ignored. If PERL5OPT begins with
1034 B<-T>, tainting will be enabled and subsequent options ignored. If
1035 PERL5OPT begins with B<-t>, tainting will be enabled, a writable dot
1036 removed from @INC, and subsequent options honored.
1041 A space (or colon) separated list of PerlIO layers. If perl is built
1042 to use PerlIO system for IO (the default) these layers affect Perl's IO.
1044 It is conventional to start layer names with a colon (for example, C<:perlio>) to
1045 emphasize their similarity to variable "attributes". But the code that parses
1046 layer specification strings, which is also used to decode the PERLIO
1047 environment variable, treats the colon as a separator.
1049 An unset or empty PERLIO is equivalent to the default set of layers for
1050 your platform; for example, C<:unix:perlio> on Unix-like systems
1051 and C<:unix:crlf> on Windows and other DOS-like systems.
1053 The list becomes the default for I<all> Perl's IO. Consequently only built-in
1054 layers can appear in this list, as external layers (such as C<:encoding()>) need
1055 IO in order to load them! See L<"open pragma"|open> for how to add external
1056 encodings as defaults.
1058 Layers it makes sense to include in the PERLIO environment
1059 variable are briefly summarized below. For more details see L<PerlIO>.
1066 A pseudolayer that turns the C<:utf8> flag I<off> for the layer below;
1067 unlikely to be useful on its own in the global PERLIO environment variable.
1068 You perhaps were thinking of C<:crlf:bytes> or C<:perlio:bytes>.
1073 A layer which does CRLF to C<"\n"> translation distinguishing "text" and
1074 "binary" files in the manner of MS-DOS and similar operating systems.
1075 (It currently does I<not> mimic MS-DOS as far as treating of Control-Z
1076 as being an end-of-file marker.)
1081 A layer that implements "reading" of files by using I<mmap>(2) to
1082 make an entire file appear in the process's address space, and then
1083 using that as PerlIO's "buffer".
1088 This is a re-implementation of stdio-like buffering written as a
1089 PerlIO layer. As such it will call whatever layer is below it for
1090 its operations, typically C<:unix>.
1095 An experimental pseudolayer that removes the topmost layer.
1096 Use with the same care as is reserved for nitroglycerine.
1101 A pseudolayer that manipulates other layers. Applying the C<:raw>
1102 layer is equivalent to calling C<binmode($fh)>. It makes the stream
1103 pass each byte as-is without translation. In particular, both CRLF
1104 translation and intuiting C<:utf8> from the locale are disabled.
1106 Unlike in earlier versions of Perl, C<:raw> is I<not>
1107 just the inverse of C<:crlf>: other layers which would affect the
1108 binary nature of the stream are also removed or disabled.
1113 This layer provides a PerlIO interface by wrapping system's ANSI C "stdio"
1114 library calls. The layer provides both buffering and IO.
1115 Note that the C<:stdio> layer does I<not> do CRLF translation even if that
1116 is the platform's normal behaviour. You will need a C<:crlf> layer above it
1122 Low-level layer that calls C<read>, C<write>, C<lseek>, etc.
1127 A pseudolayer that enables a flag in the layer below to tell Perl
1128 that output should be in utf8 and that input should be regarded as
1129 already in valid utf8 form. B<WARNING: It does not check for validity and as such
1130 should be handled with extreme caution for input, because security violations
1131 can occur with non-shortest UTF-8 encodings, etc.> Generally C<:encoding(UTF-8)> is
1132 the best option when reading UTF-8 encoded data.
1137 On Win32 platforms this I<experimental> layer uses native "handle" IO
1138 rather than a Unix-like numeric file descriptor layer. Known to be
1139 buggy in this release (5.14).
1143 The default set of layers should give acceptable results on all platforms
1145 For Unix platforms that will be the equivalent of "unix perlio" or "stdio".
1146 Configure is set up to prefer the "stdio" implementation if the system's library
1147 provides for fast access to the buffer; otherwise, it uses the "unix perlio"
1150 On Win32 the default in this release (5.14) is "unix crlf". Win32's "stdio"
1151 has a number of bugs/mis-features for Perl IO which are somewhat depending
1152 on the version and vendor of the C compiler. Using our own C<crlf> layer as
1153 the buffer avoids those issues and makes things more uniform. The C<crlf>
1154 layer provides CRLF conversion as well as buffering.
1156 This release (5.14) uses C<unix> as the bottom layer on Win32, and so still
1157 uses the C compiler's numeric file descriptor routines. There is an
1158 experimental native C<win32> layer, which is expected to be enhanced and
1159 should eventually become the default under Win32.
1161 The PERLIO environment variable is completely ignored when Perl
1162 is run in taint mode.
1167 If set to the name of a file or device when Perl is run with the
1168 B<-Di> command-line switch, the logging of certain operations of
1169 the PerlIO subsystem will be redirected to the specified file rather
1170 than going to stderr, which is the default. The file is opened in append
1171 mode. Typical uses are in Unix:
1173 % env PERLIO_DEBUG=/tmp/perlio.log perl -Di script ...
1175 and under Win32, the approximately equivalent:
1177 > set PERLIO_DEBUG=CON
1180 This functionality is disabled for setuid scripts, for scripts run
1181 with B<-T>, and for scripts run on a Perl built without C<-DDEBUGGING>
1187 A list of directories in which to look for Perl library
1188 files before looking in the standard library.
1189 If PERL5LIB is defined, PERLLIB is not used.
1191 The PERLLIB environment variable is completely ignored when Perl
1192 is run in taint mode.
1197 The command used to load the debugger code. The default is:
1199 BEGIN { require "perl5db.pl" }
1201 The PERL5DB environment variable is only used when Perl is started with
1202 a bare B<-d> switch.
1204 =item PERL5DB_THREADED
1207 If set to a true value, indicates to the debugger that the code being
1208 debugged uses threads.
1210 =item PERL5SHELL (specific to the Win32 port)
1213 On Win32 ports only, may be set to an alternative shell that Perl must use
1214 internally for executing "backtick" commands or system(). Default is
1215 C<cmd.exe /x/d/c> on WindowsNT and C<command.com /c> on Windows95. The
1216 value is considered space-separated. Precede any character that
1217 needs to be protected, like a space or backslash, with another backslash.
1219 Note that Perl doesn't use COMSPEC for this purpose because
1220 COMSPEC has a high degree of variability among users, leading to
1221 portability concerns. Besides, Perl can use a shell that may not be
1222 fit for interactive use, and setting COMSPEC to such a shell may
1223 interfere with the proper functioning of other programs (which usually
1224 look in COMSPEC to find a shell fit for interactive use).
1226 Before Perl 5.10.0 and 5.8.8, PERL5SHELL was not taint checked
1227 when running external commands. It is recommended that
1228 you explicitly set (or delete) C<$ENV{PERL5SHELL}> when running
1229 in taint mode under Windows.
1231 =item PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
1232 X<PERL_ALLOW_NON_IFS_LSP>
1234 Set to 1 to allow the use of non-IFS compatible LSPs (Layered Service Providers).
1235 Perl normally searches for an IFS-compatible LSP because this is required
1236 for its emulation of Windows sockets as real filehandles. However, this may
1237 cause problems if you have a firewall such as I<McAfee Guardian>, which requires
1238 that all applications use its LSP but which is not IFS-compatible, because clearly
1239 Perl will normally avoid using such an LSP.
1241 Setting this environment variable to 1 means that Perl will simply use the
1242 first suitable LSP enumerated in the catalog, which keeps I<McAfee Guardian>
1243 happy--and in that particular case Perl still works too because I<McAfee
1244 Guardian>'s LSP actually plays other games which allow applications
1245 requiring IFS compatibility to work.
1247 =item PERL_DEBUG_MSTATS
1248 X<PERL_DEBUG_MSTATS>
1250 Relevant only if Perl is compiled with the C<malloc> included with the Perl
1251 distribution; that is, if C<perl -V:d_mymalloc> is "define".
1253 If set, this dumps out memory statistics after execution. If set
1254 to an integer greater than one, also dumps out memory statistics
1257 =item PERL_DESTRUCT_LEVEL
1258 X<PERL_DESTRUCT_LEVEL>
1260 Relevant only if your Perl executable was built with B<-DDEBUGGING>,
1261 this controls the behaviour of global destruction of objects and other
1262 references. See L<perlhacktips/PERL_DESTRUCT_LEVEL> for more information.
1264 =item PERL_DL_NONLAZY
1267 Set to C<"1"> to have Perl resolve I<all> undefined symbols when it loads
1268 a dynamic library. The default behaviour is to resolve symbols when
1269 they are used. Setting this variable is useful during testing of
1270 extensions, as it ensures that you get an error on misspelled function
1271 names even if the test suite doesn't call them.
1276 If using the C<use encoding> pragma without an explicit encoding name, the
1277 PERL_ENCODING environment variable is consulted for an encoding name.
1279 =item PERL_HASH_SEED
1282 (Since Perl 5.8.1, new semantics in Perl 5.18.0) Used to override
1283 the randomization of Perl's internal hash function. The value is expressed
1284 in hexadecimal, and may include a leading 0x. Truncated patterns
1285 are treated as though they are suffixed with sufficient 0's as required.
1287 If the option is provided, and C<PERL_PERTURB_KEYS> is NOT set, then
1288 a value of '0' implies C<PERL_PERTURB_KEYS=0> and any other value
1289 implies C<PERL_PERTURB_KEYS=2>.
1291 B<PLEASE NOTE: The hash seed is sensitive information>. Hashes are
1292 randomized to protect against local and remote attacks against Perl
1293 code. By manually setting a seed, this protection may be partially or
1296 See L<perlsec/"Algorithmic Complexity Attacks">, L</PERL_PERTURB_KEYS>, and
1297 L</PERL_HASH_SEED_DEBUG> for more information.
1299 =item PERL_PERTURB_KEYS
1300 X<PERL_PERTURB_KEYS>
1302 (Since Perl 5.18.0) Set to C<"0"> or C<"NO"> then traversing keys
1303 will be repeatable from run to run for the same PERL_HASH_SEED.
1304 Insertion into a hash will not change the order, except to provide
1305 for more space in the hash. When combined with setting PERL_HASH_SEED
1306 this mode is as close to pre 5.18 behavior as you can get.
1308 When set to C<"1"> or C<"RANDOM"> then traversing keys will be randomized.
1309 Every time a hash is inserted into the key order will change in a random
1310 fashion. The order may not be repeatable in a following program run
1311 even if the PERL_HASH_SEED has been specified. This is the default
1314 When set to C<"2"> or C<"DETERMINISTIC"> then inserting keys into a hash
1315 will cause the key order to change, but in a way that is repeatable
1316 from program run to program run.
1318 B<NOTE:> Use of this option is considered insecure, and is intended only
1319 for debugging non-deterministic behavior in Perl's hash function. Do
1320 not use it in production.
1322 See L<perlsec/"Algorithmic Complexity Attacks"> and L</PERL_HASH_SEED>
1323 and L</PERL_HASH_SEED_DEBUG> for more information. You can get and set the
1324 key traversal mask for a specific hash by using the C<hash_traversal_mask()>
1325 function from L<Hash::Util>.
1327 =item PERL_HASH_SEED_DEBUG
1328 X<PERL_HASH_SEED_DEBUG>
1330 (Since Perl 5.8.1.) Set to C<"1"> to display (to STDERR) information
1331 about the hash function, seed, and what type of key traversal
1332 randomization is in effect at the beginning of execution. This, combined
1333 with L</PERL_HASH_SEED> and L</PERL_PERTURB_KEYS> is intended to aid in
1334 debugging nondeterministic behaviour caused by hash randomization.
1336 B<Note> that any information about the hash function, especially the hash
1337 seed is B<sensitive information>: by knowing it, one can craft a denial-of-service
1338 attack against Perl code, even remotely; see L<perlsec/"Algorithmic Complexity Attacks">
1339 for more information. B<Do not disclose the hash seed> to people who
1340 don't need to know it. See also C<hash_seed()> and
1341 C<key_traversal_mask()> in L<Hash::Util>.
1343 An example output might be:
1345 HASH_FUNCTION = ONE_AT_A_TIME_HARD HASH_SEED = 0x652e9b9349a7a032 PERTURB_KEYS = 1 (RANDOM)
1350 If your Perl was configured with B<-Accflags=-DPERL_MEM_LOG>, setting
1351 the environment variable C<PERL_MEM_LOG> enables logging debug
1352 messages. The value has the form C<< <I<number>>[m][s][t] >>, where
1353 C<I<number>> is the file descriptor number you want to write to (2 is
1354 default), and the combination of letters specifies that you want
1355 information about (m)emory and/or (s)v, optionally with
1356 (t)imestamps. For example, C<PERL_MEM_LOG=1mst> logs all
1357 information to stdout. You can write to other opened file descriptors
1358 in a variety of ways:
1360 $ 3>foo3 PERL_MEM_LOG=3m perl ...
1362 =item PERL_ROOT (specific to the VMS port)
1365 A translation-concealed rooted logical name that contains Perl and the
1366 logical device for the @INC path on VMS only. Other logical names that
1367 affect Perl on VMS include PERLSHR, PERL_ENV_TABLES, and
1368 SYS$TIMEZONE_DIFFERENTIAL, but are optional and discussed further in
1369 L<perlvms> and in F<README.vms> in the Perl source distribution.
1374 Available in Perls 5.8.1 and later. If set to C<"unsafe">, the pre-Perl-5.8.0
1375 signal behaviour (which is immediate but unsafe) is restored. If set
1376 to C<safe>, then safe (but deferred) signals are used. See
1377 L<perlipc/"Deferred Signals (Safe Signals)">.
1382 Equivalent to the B<-C> command-line switch. Note that this is not
1383 a boolean variable. Setting this to C<"1"> is not the right way to
1384 "enable Unicode" (whatever that would mean). You can use C<"0"> to
1385 "disable Unicode", though (or alternatively unset PERL_UNICODE in
1386 your shell before starting Perl). See the description of the B<-C>
1387 switch for more information.
1389 =item PERL_USE_UNSAFE_INC
1390 X<PERL_USE_UNSAFE_INC>
1392 If perl has been configured to not have the current directory in
1393 L<C<@INC>|perlvar/@INC> by default, this variable can be set to C<"1">
1394 to reinstate it. It's primarily intended for use while building and
1395 testing modules that have not been updated to deal with "." not being in
1396 C<@INC> and should not be set in the environment for day-to-day use.
1398 =item SYS$LOGIN (specific to the VMS port)
1401 Used if chdir has no argument and HOME and LOGDIR are not set.
1403 =item PERL_INTERNAL_RAND_SEED
1404 X<PERL_INTERNAL_RAND_SEED>
1406 Set to a non-negative integer to seed the random number generator used
1407 internally by perl for a variety of purposes.
1409 Ignored if perl is run setuid or setgid. Used only for some limited
1410 startup randomization (hash keys) if C<-T> or C<-t> perl is started
1411 with tainting enabled.
1413 Perl may be built to ignore this variable.
1417 Perl also has environment variables that control how Perl handles data
1418 specific to particular natural languages; see L<perllocale>.
1420 Perl and its various modules and components, including its test frameworks,
1421 may sometimes make use of certain other environment variables. Some of
1422 these are specific to a particular platform. Please consult the
1423 appropriate module documentation and any documentation for your platform
1424 (like L<perlsolaris>, L<perllinux>, L<perlmacosx>, L<perlwin32>, etc) for
1425 variables peculiar to those specific situations.
1427 Perl makes all environment variables available to the program being
1428 executed, and passes these along to any child processes it starts.
1429 However, programs running setuid would do well to execute the following
1430 lines before doing anything else, just to keep people honest:
1432 $ENV{PATH} = "/bin:/usr/bin"; # or whatever you need
1433 $ENV{SHELL} = "/bin/sh" if exists $ENV{SHELL};
1434 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};