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 L<-e|/-e commandline> or L<-E|/-E commandline>
32 switches on the command line.
36 Contained in the file specified by the first filename on the command line.
37 (Note that systems supporting the C<#!> notation invoke interpreters this
38 way. See L</Location of Perl>.)
42 Passed in implicitly via standard input. This works only if there are
43 no filename arguments--to pass arguments to a STDIN-read program you
44 must explicitly specify a "-" for the program name.
48 With methods 2 and 3, Perl starts parsing the input file from the
49 beginning, unless you've specified a L</-x> switch, in which case it
50 scans for the first line starting with C<#!> and containing the word
51 "perl", and starts there instead. This is useful for running a program
52 embedded in a larger message. (In this case you would indicate the end
53 of the program using the C<__END__> token.)
55 The C<#!> line is always examined for switches as the line is being
56 parsed. Thus, if you're on a machine that allows only one argument
57 with the C<#!> line, or worse, doesn't even recognize the C<#!> line, you
58 still can get consistent switch behaviour regardless of how Perl was
59 invoked, even if L</-x> was used to find the beginning of the program.
61 Because historically some operating systems silently chopped off
62 kernel interpretation of the C<#!> line after 32 characters, some
63 switches may be passed in on the command line, and some may not;
64 you could even get a "-" without its letter, if you're not careful.
65 You probably want to make sure that all your switches fall either
66 before or after that 32-character boundary. Most switches don't
67 actually care if they're processed redundantly, but getting a "-"
68 instead of a complete switch could cause Perl to try to execute
69 standard input instead of your program. And a partial L<-I|/-Idirectory>
70 switch could also cause odd results.
72 Some switches do care if they are processed twice, for instance
73 combinations of L<-l|/-l[octnum]> and L<-0|/-0[octalE<sol>hexadecimal]>.
74 Either put all the switches after the 32-character boundary (if
75 applicable), or replace the use of B<-0>I<digits> by
76 C<BEGIN{ $/ = "\0digits"; }>.
78 Parsing of the C<#!> switches starts wherever "perl" is mentioned in the line.
79 The sequences "-*" and "- " are specifically ignored so that you could,
80 if you were so inclined, say
84 eval 'exec perl -x -wS $0 ${1+"$@"}'
87 to let Perl see the L</-p> switch.
89 A similar trick involves the I<env> program, if you have it.
93 The examples above use a relative path to the perl interpreter,
94 getting whatever version is first in the user's path. If you want
95 a specific version of Perl, say, perl5.14.1, you should place
96 that directly in the C<#!> line's path.
98 If the C<#!> line does not contain the word "perl" nor the word "indir",
99 the program named after the C<#!> is executed instead of the Perl
100 interpreter. This is slightly bizarre, but it helps people on machines
101 that don't do C<#!>, because they can tell a program that their SHELL is
102 F</usr/bin/perl>, and Perl will then dispatch the program to the correct
103 interpreter for them.
105 After locating your program, Perl compiles the entire program to an
106 internal form. If there are any compilation errors, execution of the
107 program is not attempted. (This is unlike the typical shell script,
108 which might run part-way through before finding a syntax error.)
110 If the program is syntactically correct, it is executed. If the program
111 runs off the end without hitting an exit() or die() operator, an implicit
112 C<exit(0)> is provided to indicate successful completion.
114 =head2 #! and quoting on non-Unix systems
117 Unix's C<#!> technique can be simulated on other systems:
125 extproc perl -S -your_switches
127 as the first line in C<*.cmd> file (L</-S> due to a bug in cmd.exe's
132 Create a batch file to run your program, and codify it in
133 C<ALTERNATE_SHEBANG> (see the F<dosish.h> file in the source
134 distribution for more information).
138 The Win95/NT installation, when using the ActiveState installer for Perl,
139 will modify the Registry to associate the F<.pl> extension with the perl
140 interpreter. If you install Perl by other means (including building from
141 the sources), you may have to modify the Registry yourself. Note that
142 this means you can no longer tell the difference between an executable
143 Perl program and a Perl library file.
149 $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
150 $ exit++ + ++$status != 0 and $exit = $status = undef;
152 at the top of your program, where B<-mysw> are any command line switches you
153 want to pass to Perl. You can now invoke the program directly, by saying
154 C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly
155 via F<DCL$PATH> by just using the name of the program).
157 This incantation is a bit much to remember, but Perl will display it for
158 you if you say C<perl "-V:startperl">.
162 Command-interpreters on non-Unix systems have rather different ideas
163 on quoting than Unix shells. You'll need to learn the special
164 characters in your command-interpreter (C<*>, C<\> and C<"> are
165 common) and how to protect whitespace and these characters to run
166 one-liners (see L<-e|/-e commandline> below).
168 On some systems, you may have to change single-quotes to double ones,
169 which you must I<not> do on Unix or Plan 9 systems. You might also
170 have to change a single % to a %%.
175 perl -e 'print "Hello world\n"'
178 perl -e "print \"Hello world\n\""
181 perl -e "print ""Hello world\n"""
183 The problem is that none of this is reliable: it depends on the
184 command and it is entirely possible neither works. If I<4DOS> were
185 the command shell, this would probably work better:
187 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
189 B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in
190 when nobody was looking, but just try to find documentation for its
193 There is no general solution to all of this. It's just a mess.
195 =head2 Location of Perl
196 X<perl, location of interpreter>
198 It may seem obvious to say, but Perl is useful only when users can
199 easily find it. When possible, it's good for both F</usr/bin/perl>
200 and F</usr/local/bin/perl> to be symlinks to the actual binary. If
201 that can't be done, system administrators are strongly encouraged
202 to put (symlinks to) perl and its accompanying utilities into a
203 directory typically found along a user's PATH, or in some other
204 obvious and convenient place.
206 In this documentation, C<#!/usr/bin/perl> on the first line of the program
207 will stand in for whatever method works on your system. You are
208 advised to use a specific path if you care about a specific version.
210 #!/usr/local/bin/perl5.14
212 or if you just want to be running at least version, place a statement
213 like this at the top of your program:
217 =head2 Command Switches
218 X<perl, command switches> X<command switches>
220 As with all standard commands, a single-character switch may be
221 clustered with the following switch, if any.
223 #!/usr/bin/perl -spi.orig # same as -s -p -i.orig
225 A C<--> signals the end of options and disables further option processing. Any
226 arguments after the C<--> are treated as filenames and arguments.
232 =item B<-0>[I<octal/hexadecimal>]
235 specifies the input record separator (C<$/>) as an octal or
236 hexadecimal number. If there are no digits, the null character is the
237 separator. Other switches may precede or follow the digits. For
238 example, if you have a version of I<find> which can print filenames
239 terminated by the null character, you can say this:
241 find . -name '*.orig' -print0 | perl -n0e unlink
243 The special value 00 will cause Perl to slurp files in paragraph mode.
244 Any value 0400 or above will cause Perl to slurp files whole, but by convention
245 the value 0777 is the one normally used for this purpose.
247 You can also specify the separator character using hexadecimal notation:
248 B<-0xI<HHH...>>, where the C<I<H>> are valid hexadecimal digits. Unlike
249 the octal form, this one may be used to specify any Unicode character, even
250 those beyond 0xFF. So if you I<really> want a record separator of 0777,
251 specify it as B<-0x1FF>. (This means that you cannot use the L</-x> option
252 with a directory name that consists of hexadecimal digits, or else Perl
253 will think you have specified a hex number to B<-0>.)
258 turns on autosplit mode when used with a L</-n> or L</-p>. An implicit
259 split command to the @F array is done as the first thing inside the
260 implicit while loop produced by the L</-n> or L</-p>.
262 perl -ane 'print pop(@F), "\n";'
271 An alternate delimiter may be specified using L<-F|/-Fpattern>.
273 B<-a> implicitly sets L</-n>.
275 =item B<-C [I<number/list>]>
278 The B<-C> flag controls some of the Perl Unicode features.
280 As of 5.8.1, the B<-C> can be followed either by a number or a list
281 of option letters. The letters, their numeric values, and effects
282 are as follows; listing the letters is equal to summing the numbers.
284 I 1 STDIN is assumed to be in UTF-8
285 O 2 STDOUT will be in UTF-8
286 E 4 STDERR will be in UTF-8
288 i 8 UTF-8 is the default PerlIO layer for input streams
289 o 16 UTF-8 is the default PerlIO layer for output streams
291 A 32 the @ARGV elements are expected to be strings encoded
293 L 64 normally the "IOEioA" are unconditional, the L makes
294 them conditional on the locale environment variables
295 (the LC_ALL, LC_CTYPE, and LANG, in the order of
296 decreasing precedence) -- if the variables indicate
297 UTF-8, then the selected "IOEioA" are in effect
298 a 256 Set ${^UTF8CACHE} to -1, to run the UTF-8 caching
299 code in debugging mode.
301 =for documenting_the_underdocumented
302 perl.h gives W/128 as PERL_UNICODE_WIDESYSCALLS "/* for Sarathy */"
305 perltodo mentions Unicode in %ENV and filenames. I guess that these will be
306 options e and f (or F).
308 For example, B<-COE> and B<-C6> will both turn on UTF-8-ness on both
309 STDOUT and STDERR. Repeating letters is just redundant, not cumulative
312 The C<io> options mean that any subsequent open() (or similar I/O
313 operations) in main program scope will have the C<:utf8> PerlIO layer
314 implicitly applied to them, in other words, UTF-8 is expected from any
315 input stream, and UTF-8 is produced to any output stream. This is just
316 the default set via L<C<${^OPEN}>|perlvar/${^OPEN}>,
317 with explicit layers in open() and with binmode() one can
318 manipulate streams as usual. This has no effect on code run in modules.
320 B<-C> on its own (not followed by any number or option list), or the
321 empty string C<""> for the L</PERL_UNICODE> environment variable, has the
322 same effect as B<-CSDL>. In other words, the standard I/O handles and
323 the default C<open()> layer are UTF-8-fied I<but> only if the locale
324 environment variables indicate a UTF-8 locale. This behaviour follows
325 the I<implicit> (and problematic) UTF-8 behaviour of Perl 5.8.0.
326 (See L<perl581delta/UTF-8 no longer default under UTF-8 locales>.)
328 You can use B<-C0> (or C<"0"> for C<PERL_UNICODE>) to explicitly
329 disable all the above Unicode features.
331 The read-only magic variable C<${^UNICODE}> reflects the numeric value
332 of this setting. This variable is set during Perl startup and is
333 thereafter read-only. If you want runtime effects, use the three-arg
334 open() (see L<perlfunc/open>), the two-arg binmode() (see L<perlfunc/binmode>),
335 and the C<open> pragma (see L<open>).
337 (In Perls earlier than 5.8.1 the B<-C> switch was a Win32-only switch
338 that enabled the use of Unicode-aware "wide system call" Win32 APIs.
339 This feature was practically unused, however, and the command line
340 switch was therefore "recycled".)
342 B<Note:> Since perl 5.10.1, if the B<-C> option is used on the C<#!> line,
343 it must be specified on the command line as well, since the standard streams
344 are already set up at this point in the execution of the perl interpreter.
345 You can also use binmode() to set the encoding of an I/O stream.
350 causes Perl to check the syntax of the program and then exit without
351 executing it. Actually, it I<will> execute any C<BEGIN>, C<UNITCHECK>,
352 or C<CHECK> blocks and any C<use> statements: these are considered as
353 occurring outside the execution of your program. C<INIT> and C<END>
354 blocks, however, will be skipped.
361 runs the program under the Perl debugger. See L<perldebug>.
362 If B<t> is specified, it indicates to the debugger that threads
363 will be used in the code being debugged.
365 =item B<-d:>I<MOD[=bar,baz]>
368 =item B<-dt:>I<MOD[=bar,baz]>
370 runs the program under the control of a debugging, profiling, or tracing
371 module installed as C<Devel::I<MOD>>. E.g., B<-d:DProf> executes the
372 program using the C<Devel::DProf> profiler. As with the L<-M|/-M[-]module>
373 flag, options may be passed to the C<Devel::I<MOD>> package where they will
374 be received and interpreted by the C<Devel::I<MOD>::import> routine. Again,
375 like B<-M>, use -B<-d:-I<MOD>> to call C<Devel::I<MOD>::unimport> instead of
376 import. The comma-separated list of options must follow a C<=> character.
377 If B<t> is specified, it indicates to the debugger that threads will be used
378 in the code being debugged. See L<perldebug>.
380 =item B<-D>I<letters>
381 X<-D> X<DEBUGGING> X<-DDEBUGGING>
385 sets debugging flags. This switch is enabled only if your perl binary has
386 been built with debugging enabled: normal production perls won't have
389 For example, to watch how perl executes your program, use B<-Dtls>.
390 Another nice value is B<-Dx>, which lists your compiled syntax tree, and
391 B<-Dr> displays compiled regular expressions; the format of the output is
392 explained in L<perldebguts>.
394 As an alternative, specify a number instead of list of letters (e.g.,
395 B<-D14> is equivalent to B<-Dtls>):
397 1 p Tokenizing and parsing (with v, displays parse
399 2 s Stack snapshots (with v, displays all stacks)
400 4 l Context (loop) stack processing
402 16 o Method and overloading resolution
403 32 c String/numeric conversions
404 64 P Print profiling info, source file input state
405 128 m Memory and SV allocation
406 256 f Format processing
407 512 r Regular expression parsing and execution
408 1024 x Syntax tree dump
409 2048 u Tainting checks
410 4096 U Unofficial, User hacking (reserved for private,
412 16384 X Scratchpad allocation
414 65536 S Op slab allocation
416 262144 R Include reference counts of dumped variables
418 524288 J show s,t,P-debug (don't Jump over) on opcodes within
420 1048576 v Verbose: use in conjunction with other flags to
421 increase the verbosity of the output. Is a no-op on
422 many of the other flags
423 2097152 C Copy On Write
424 4194304 A Consistency checks on internal structures
425 8388608 q quiet - currently only suppresses the "EXECUTING"
427 16777216 M trace smart match resolution
428 33554432 B dump suBroutine definitions, including special
430 67108864 L trace Locale-related info; what gets output is very
432 134217728 i trace PerlIO layer processing. Set PERLIO_DEBUG to
433 the filename to trace to.
434 268435456 y trace y///, tr/// compilation and execution
436 All these flags require B<-DDEBUGGING> when you compile the Perl
437 executable (but see C<:opd> in L<Devel::Peek> or L<re/'debug' mode>
438 which may change this).
439 See the F<INSTALL> file in the Perl source distribution
442 If you're just trying to get a print out of each line of Perl code
443 as it executes, the way that C<sh -x> provides for shell scripts,
444 you can't use Perl's B<-D> switch. Instead do this
446 # If you have "env" utility
447 env PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
449 # Bourne shell syntax
450 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
453 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
455 See L<perldebug> for details and variations.
457 =item B<-e> I<commandline>
460 may be used to enter one line of program. If B<-e> is given, Perl
461 will not look for a filename in the argument list. Multiple B<-e>
462 commands may be given to build up a multi-line script. Make sure
463 to use semicolons where you would in a normal program.
465 =item B<-E> I<commandline>
468 behaves just like L<-e|/-e commandline>, except that it implicitly
469 enables all optional features (in the main compilation unit). See
473 X<-f> X<sitecustomize> X<sitecustomize.pl>
475 Disable executing F<$Config{sitelib}/sitecustomize.pl> at startup.
477 Perl can be built so that it by default will try to execute
478 F<$Config{sitelib}/sitecustomize.pl> at startup (in a BEGIN block).
479 This is a hook that allows the sysadmin to customize how Perl behaves.
480 It can for instance be used to add entries to the @INC array to make Perl
481 find modules in non-standard locations.
483 Perl actually inserts the following code:
486 do { local $!; -f "$Config{sitelib}/sitecustomize.pl"; }
487 && do "$Config{sitelib}/sitecustomize.pl";
490 Since it is an actual C<do> (not a C<require>), F<sitecustomize.pl>
491 doesn't need to return a true value. The code is run in package C<main>,
492 in its own lexical scope. However, if the script dies, C<$@> will not
495 The value of C<$Config{sitelib}> is also determined in C code and not
496 read from C<Config.pm>, which is not loaded.
498 The code is executed I<very> early. For example, any changes made to
499 C<@INC> will show up in the output of `perl -V`. Of course, C<END>
500 blocks will be likewise executed very late.
502 To determine at runtime if this capability has been compiled in your
503 perl, you can check the value of C<$Config{usesitecustomize}>.
505 =item B<-F>I<pattern>
508 specifies the pattern to split on for L</-a>. The pattern may be
509 surrounded by C<//>, C<"">, or C<''>, otherwise it will be put in single
510 quotes. You can't use literal whitespace or NUL characters in the pattern.
512 B<-F> implicitly sets both L</-a> and L</-n>.
517 prints a summary of the options.
519 =item B<-i>[I<extension>]
522 specifies that files processed by the C<E<lt>E<gt>> construct are to be
523 edited in-place. It does this by renaming the input file, opening the
524 output file by the original name, and selecting that output file as the
525 default for print() statements. The extension, if supplied, is used to
526 modify the name of the old file to make a backup copy, following these
529 If no extension is supplied, and your system supports it, the original
530 I<file> is kept open without a name while the output is redirected to
531 a new file with the original I<filename>. When perl exits, cleanly or not,
532 the original I<file> is unlinked.
534 If the extension doesn't contain a C<*>, then it is appended to the
535 end of the current filename as a suffix. If the extension does
536 contain one or more C<*> characters, then each C<*> is replaced
537 with the current filename. In Perl terms, you could think of this
540 ($backup = $extension) =~ s/\*/$file_name/g;
542 This allows you to add a prefix to the backup file, instead of (or in
543 addition to) a suffix:
545 $ perl -pi'orig_*' -e 's/bar/baz/' fileA # backup to
548 Or even to place backup copies of the original files into another
549 directory (provided the directory already exists):
551 $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to
554 These sets of one-liners are equivalent:
556 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
557 $ perl -pi'*' -e 's/bar/baz/' fileA # overwrite current file
559 $ perl -pi'.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
560 $ perl -pi'*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
562 From the shell, saying
564 $ perl -p -i.orig -e "s/foo/bar/; ... "
566 is the same as using the program:
568 #!/usr/bin/perl -pi.orig
571 which is equivalent to
574 $extension = '.orig';
576 if ($ARGV ne $oldargv) {
577 if ($extension !~ /\*/) {
578 $backup = $ARGV . $extension;
581 ($backup = $extension) =~ s/\*/$ARGV/g;
583 rename($ARGV, $backup);
584 open(ARGVOUT, ">$ARGV");
591 print; # this prints to original filename
595 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
596 know when the filename has changed. It does, however, use ARGVOUT for
597 the selected filehandle. Note that STDOUT is restored as the default
598 output filehandle after the loop.
600 As shown above, Perl creates the backup file whether or not any output
601 is actually changed. So this is just a fancy way to copy files:
603 $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
605 $ perl -p -i'.orig' -e 1 file1 file2 file3...
607 You can use C<eof> without parentheses to locate the end of each input
608 file, in case you want to append to each file, or reset line numbering
609 (see example in L<perlfunc/eof>).
611 If, for a given file, Perl is unable to create the backup file as
612 specified in the extension then it will skip that file and continue on
613 with the next one (if it exists).
615 For a discussion of issues surrounding file permissions and B<-i>, see
616 L<perlfaq5/Why does Perl let me delete read-only files? Why does -i clobber
617 protected files? Isn't this a bug in Perl?>.
619 You cannot use B<-i> to create directories or to strip extensions from
622 Perl does not expand C<~> in filenames, which is good, since some
623 folks use it for their backup files:
625 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
627 Note that because B<-i> renames or deletes the original file before
628 creating a new file of the same name, Unix-style soft and hard links will
631 Finally, the B<-i> switch does not impede execution when no
632 files are given on the command line. In this case, no backup is made
633 (the original file cannot, of course, be determined) and processing
634 proceeds from STDIN to STDOUT as might be expected.
636 =item B<-I>I<directory>
639 Directories specified by B<-I> are prepended to the search path for
642 =item B<-l>[I<octnum>]
645 enables automatic line-ending processing. It has two separate
646 effects. First, it automatically chomps C<$/> (the input record
647 separator) when used with L</-n> or L</-p>. Second, it assigns C<$\>
648 (the output record separator) to have the value of I<octnum> so
649 that any print statements will have that separator added back on.
650 If I<octnum> is omitted, sets C<$\> to the current value of
651 C<$/>. For instance, to trim lines to 80 columns:
653 perl -lpe 'substr($_, 80) = ""'
655 Note that the assignment C<$\ = $/> is done when the switch is processed,
656 so the input record separator can be different than the output record
657 separator if the B<-l> switch is followed by a
658 L<-0|/-0[octalE<sol>hexadecimal]> switch:
660 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
662 This sets C<$\> to newline and then sets C<$/> to the null character.
664 =item B<-m>[B<->]I<module>
667 =item B<-M>[B<->]I<module>
669 =item B<-M>[B<->]I<'module ...'>
671 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
673 B<-m>I<module> executes C<use> I<module> C<();> before executing your
674 program. This loads the module, but does not call its C<import> method,
675 so does not import subroutines and does not give effect to a pragma.
677 B<-M>I<module> executes C<use> I<module> C<;> before executing your
678 program. This loads the module and calls its C<import> method, causing
679 the module to have its default effect, typically importing subroutines
680 or giving effect to a pragma.
681 You can use quotes to add extra code after the module name,
682 e.g., C<'-MI<MODULE> qw(foo bar)'>.
684 If the first character after the B<-M> or B<-m> is a dash (B<->)
685 then the 'use' is replaced with 'no'.
686 This makes no difference for B<-m>.
688 A little builtin syntactic sugar means you can also say
689 B<-mI<MODULE>=foo,bar> or B<-MI<MODULE>=foo,bar> as a shortcut for
690 B<'-MI<MODULE> qw(foo bar)'>. This avoids the need to use quotes when
691 importing symbols. The actual code generated by B<-MI<MODULE>=foo,bar> is
692 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
693 removes the distinction between B<-m> and B<-M>; that is,
694 B<-mI<MODULE>=foo,bar> is the same as B<-MI<MODULE>=foo,bar>.
696 A consequence of the C<split> formulation
697 is that B<-MI<MODULE>=number> never does a version check,
698 unless C<I<MODULE>::import()> itself is set up to do a version check, which
699 could happen for example if I<MODULE> inherits from L<Exporter>.
704 causes Perl to assume the following loop around your program, which
705 makes it iterate over filename arguments somewhat like I<sed -n> or
710 ... # your program goes here
713 Note that the lines are not printed by default. See L</-p> to have
714 lines printed. If a file named by an argument cannot be opened for
715 some reason, Perl warns you about it and moves on to the next file.
717 Also note that C<< <> >> passes command line arguments to
718 L<perlfunc/open>, which doesn't necessarily interpret them as file names.
719 See L<perlop> for possible security implications.
721 Here is an efficient way to delete all files that haven't been modified for
724 find . -mtime +7 -print | perl -nle unlink
726 This is faster than using the B<-exec> switch of I<find> because you don't
727 have to start a process on every filename found (but it's not faster
728 than using the B<-delete> switch available in newer versions of I<find>.
729 It does suffer from the bug of mishandling newlines in pathnames, which
730 you can fix if you follow the example under
731 L<-0|/-0[octalE<sol>hexadecimal]>.
733 C<BEGIN> and C<END> blocks may be used to capture control before or after
734 the implicit program loop, just as in I<awk>.
739 causes Perl to assume the following loop around your program, which
740 makes it iterate over filename arguments somewhat like I<sed>:
745 ... # your program goes here
747 print or die "-p destination: $!\n";
750 If a file named by an argument cannot be opened for some reason, Perl
751 warns you about it, and moves on to the next file. Note that the
752 lines are printed automatically. An error occurring during printing is
753 treated as fatal. To suppress printing use the L</-n> switch. A B<-p>
754 overrides a B<-n> switch.
756 C<BEGIN> and C<END> blocks may be used to capture control before or after
757 the implicit loop, just as in I<awk>.
762 enables rudimentary switch parsing for switches on the command
763 line after the program name but before any filename arguments (or before
764 an argument of B<-->). Any switch found there is removed from @ARGV and sets the
765 corresponding variable in the Perl program. The following program
766 prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
767 if it is invoked with B<-xyz=abc>.
770 if ($xyz) { print "$xyz\n" }
772 Do note that a switch like B<--help> creates the variable C<${-help}>, which is
773 not compliant with C<use strict "refs">. Also, when using this option on a
774 script with warnings enabled you may get a lot of spurious "used only once"
780 makes Perl use the L</PATH> environment variable to search for the
781 program unless the name of the program contains path separators.
783 On some platforms, this also makes Perl append suffixes to the
784 filename while searching for it. For example, on Win32 platforms,
785 the ".bat" and ".cmd" suffixes are appended if a lookup for the
786 original name fails, and if the name does not already end in one
787 of those suffixes. If your Perl was compiled with C<DEBUGGING> turned
788 on, using the L<-Dp|/-Dletters> switch to Perl shows how the search
791 Typically this is used to emulate C<#!> startup on platforms that don't
792 support C<#!>. It's also convenient when debugging a script that uses C<#!>,
793 and is thus normally found by the shell's $PATH search mechanism.
795 This example works on many platforms that have a shell compatible with
799 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
800 if 0; # ^ Run only under a shell
802 The system ignores the first line and feeds the program to F</bin/sh>,
803 which proceeds to try to execute the Perl program as a shell script.
804 The shell executes the second line as a normal shell command, and thus
805 starts up the Perl interpreter. On some systems $0 doesn't always
806 contain the full pathname, so the L</-S> tells Perl to search for the
807 program if necessary. After Perl locates the program, it parses the
808 lines and ignores them because the check 'if 0' is never true.
809 If the program will be interpreted by csh, you will need
810 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
811 embedded spaces (and such) in the argument list. To start up I<sh> rather
812 than I<csh>, some systems may have to replace the C<#!> line with a line
813 containing just a colon, which will be politely ignored by Perl. Other
814 systems can't control that, and need a totally devious construct that
815 will work under any of I<csh>, I<sh>, or Perl, such as the following:
817 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
818 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
819 if 0; # ^ Run only under a shell
821 If the filename supplied contains directory separators (and so is an
822 absolute or relative pathname), and if that file is not found,
823 platforms that append file extensions will do so and try to look
824 for the file with those extensions added, one by one.
826 On DOS-like platforms, if the program does not contain directory
827 separators, it will first be searched for in the current directory
828 before being searched for on the PATH. On Unix platforms, the
829 program will be searched for strictly on the PATH.
834 Like L</-T>, but taint checks will issue warnings rather than fatal
835 errors. These warnings can now be controlled normally with C<no warnings
838 B<Note: This is not a substitute for C<-T>!> This is meant to be
839 used I<only> as a temporary development aid while securing legacy code:
840 for real production code and for new secure code written from scratch,
841 always use the real L</-T>.
846 turns on "taint" so you can test them. Ordinarily
847 these checks are done only when running setuid or setgid. It's a
848 good idea to turn them on explicitly for programs that run on behalf
849 of someone else whom you might not necessarily trust, such as CGI
850 programs or any internet servers you might write in Perl. See
851 L<perlsec> for details. For security reasons, this option must be
852 seen by Perl quite early; usually this means it must appear early
853 on the command line or in the C<#!> line for systems which support
859 This switch causes Perl to dump core after compiling your
860 program. You can then in theory take this core dump and turn it
861 into an executable file by using the I<undump> program (not supplied).
862 This speeds startup at the expense of some disk space (which you
863 can minimize by stripping the executable). (Still, a "hello world"
864 executable comes out to about 200K on my machine.) If you want to
865 execute a portion of your program before dumping, use the C<CORE::dump()>
866 function instead. Note: availability of I<undump> is platform
867 specific and may not be available for a specific port of Perl.
872 allows Perl to do unsafe operations. Currently the only "unsafe"
873 operations are attempting to unlink directories while running as superuser
874 and running setuid programs with fatal taint checks turned into warnings.
875 Note that warnings must be enabled along with this option to actually
876 I<generate> the taint-check warnings.
881 prints the version and patchlevel of your perl executable.
886 prints summary of the major perl configuration values and the current
889 =item B<-V:>I<configvar>
891 Prints to STDOUT the value of the named configuration variable(s),
892 with multiples when your C<I<configvar>> argument looks like a regex (has
893 non-letters). For example:
896 libc='/lib/libc-2.2.4.so';
898 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
899 libc='/lib/libc-2.2.4.so';
901 libpth='/usr/local/lib /lib /usr/lib';
902 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
904 libc='/lib/libc-2.2.4.so';
908 Additionally, extra colons can be used to control formatting. A
909 trailing colon suppresses the linefeed and terminator ";", allowing
910 you to embed queries into shell commands. (mnemonic: PATH separator
913 $ echo "compression-vars: " `perl -V:z.*: ` " are here !"
914 compression-vars: zcat='' zip='zip' are here !
916 A leading colon removes the "name=" part of the response, this allows
917 you to map to the name you need. (mnemonic: empty label)
919 $ echo "goodvfork="`./perl -Ilib -V::usevfork`
922 Leading and trailing colons can be used together if you need
923 positional parameter values without the names. Note that in the case
924 below, the C<PERL_API> params are returned in alphabetical order.
926 $ echo building_on `perl -V::osname: -V::PERL_API_.*:` now
927 building_on 'linux' '5' '1' '9' now
932 prints warnings about dubious constructs, such as variable names
933 mentioned only once and scalar variables used
934 before being set; redefined subroutines; references to undefined
935 filehandles; filehandles opened read-only that you are attempting
936 to write on; values used as a number that don't I<look> like numbers;
937 using an array as though it were a scalar; if your subroutines
938 recurse more than 100 deep; and innumerable other things.
940 This switch really just enables the global C<$^W> variable; normally,
941 the lexically scoped C<use warnings> pragma is preferred. You
942 can disable or promote into fatal errors specific warnings using
943 C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
944 See also L<perldiag> and L<perltrap>. A fine-grained warning
945 facility is also available if you want to manipulate entire classes
946 of warnings; see L<warnings>.
951 Enables all warnings regardless of C<no warnings> or C<$^W>.
957 Disables all warnings regardless of C<use warnings> or C<$^W>.
960 Forbidden in C<L</PERL5OPT>>.
965 =item B<-x>I<directory>
967 tells Perl that the program is embedded in a larger chunk of unrelated
968 text, such as in a mail message. Leading garbage will be
969 discarded until the first line that starts with C<#!> and contains the
970 string "perl". Any meaningful switches on that line will be applied.
972 All references to line numbers by the program (warnings, errors, ...)
973 will treat the C<#!> line as the first line.
974 Thus a warning on the 2nd line of the program, which is on the 100th
975 line in the file will be reported as line 2, not as line 100.
976 This can be overridden by using the C<#line> directive.
977 (See L<perlsyn/"Plain Old Comments (Not!)">)
979 If a directory name is specified, Perl will switch to that directory
980 before running the program. The B<-x> switch controls only the
981 disposal of leading garbage. The program must be terminated with
982 C<__END__> if there is trailing garbage to be ignored; the program
983 can process any or all of the trailing garbage via the C<DATA> filehandle
986 The directory, if specified, must appear immediately following the B<-x>
987 with no intervening whitespace.
992 X<perl, environment variables>
999 Used if C<chdir> has no argument.
1004 Used if C<chdir> has no argument and L</HOME> is not set.
1009 Used in executing subprocesses, and in finding the program if L</-S> is
1015 A list of directories in which to look for Perl library files before
1016 looking in the standard library.
1017 Any architecture-specific and version-specific directories,
1018 such as F<version/archname/>, F<version/>, or F<archname/> under the
1019 specified locations are automatically included if they exist, with this
1020 lookup done at interpreter startup time. In addition, any directories
1021 matching the entries in C<$Config{inc_version_list}> are added.
1022 (These typically would be for older compatible perl versions installed
1023 in the same directory tree.)
1025 If PERL5LIB is not defined, L</PERLLIB> is used. Directories are separated
1026 (like in PATH) by a colon on Unixish platforms and by a semicolon on
1027 Windows (the proper path separator being given by the command C<perl
1030 When running taint checks, either because the program was running setuid or
1031 setgid, or the L</-T> or L</-t> switch was specified, neither PERL5LIB nor
1032 L</PERLLIB> is consulted. The program should instead say:
1034 use lib "/my/directory";
1039 Command-line options (switches). Switches in this variable are treated
1040 as if they were on every Perl command line. Only the B<-[CDIMTUWdmtw]>
1041 switches are allowed. When running taint checks (either because the
1042 program was running setuid or setgid, or because the L</-T> or L</-t>
1043 switch was used), this variable is ignored. If PERL5OPT begins with
1044 B<-T>, tainting will be enabled and subsequent options ignored. If
1045 PERL5OPT begins with B<-t>, tainting will be enabled, a writable dot
1046 removed from @INC, and subsequent options honored.
1051 A space (or colon) separated list of PerlIO layers. If perl is built
1052 to use PerlIO system for IO (the default) these layers affect Perl's IO.
1054 It is conventional to start layer names with a colon (for example, C<:perlio>) to
1055 emphasize their similarity to variable "attributes". But the code that parses
1056 layer specification strings, which is also used to decode the PERLIO
1057 environment variable, treats the colon as a separator.
1059 An unset or empty PERLIO is equivalent to the default set of layers for
1060 your platform; for example, C<:unix:perlio> on Unix-like systems
1061 and C<:unix:crlf> on Windows and other DOS-like systems.
1063 The list becomes the default for I<all> Perl's IO. Consequently only built-in
1064 layers can appear in this list, as external layers (such as C<:encoding()>) need
1065 IO in order to load them! See L<"open pragma"|open> for how to add external
1066 encodings as defaults.
1068 Layers it makes sense to include in the PERLIO environment
1069 variable are briefly summarized below. For more details see L<PerlIO>.
1076 A layer which does CRLF to C<"\n"> translation distinguishing "text" and
1077 "binary" files in the manner of MS-DOS and similar operating systems,
1078 and also provides buffering similar to C<:perlio> on these architectures.
1083 This is a re-implementation of stdio-like buffering written as a
1084 PerlIO layer. As such it will call whatever layer is below it for
1085 its operations, typically C<:unix>.
1090 This layer provides a PerlIO interface by wrapping system's ANSI C "stdio"
1091 library calls. The layer provides both buffering and IO.
1092 Note that the C<:stdio> layer does I<not> do CRLF translation even if that
1093 is the platform's normal behaviour. You will need a C<:crlf> layer above it
1099 Low-level layer that calls C<read>, C<write>, C<lseek>, etc.
1104 On Win32 platforms this I<experimental> layer uses native "handle" IO
1105 rather than a Unix-like numeric file descriptor layer. Known to be
1106 buggy in this release (5.30).
1110 The default set of layers should give acceptable results on all platforms.
1112 For Unix platforms that will be the equivalent of ":unix:perlio" or ":stdio".
1113 Configure is set up to prefer the ":stdio" implementation if the system's library
1114 provides for fast access to the buffer (not common on modern architectures);
1115 otherwise, it uses the ":unix:perlio" implementation.
1117 On Win32 the default in this release (5.30) is ":unix:crlf". Win32's ":stdio"
1118 has a number of bugs/mis-features for Perl IO which are somewhat depending
1119 on the version and vendor of the C compiler. Using our own C<:crlf> layer as
1120 the buffer avoids those issues and makes things more uniform.
1122 This release (5.30) uses C<:unix> as the bottom layer on Win32, and so still
1123 uses the C compiler's numeric file descriptor routines. There is an
1124 experimental native C<:win32> layer, which is expected to be enhanced and
1125 may eventually become the default under Win32.
1127 The PERLIO environment variable is completely ignored when Perl
1128 is run in taint mode.
1133 If set to the name of a file or device when Perl is run with the
1134 L<-Di|/-Dletters> command-line switch, the logging of certain operations
1135 of the PerlIO subsystem will be redirected to the specified file rather
1136 than going to stderr, which is the default. The file is opened in append
1137 mode. Typical uses are in Unix:
1139 % env PERLIO_DEBUG=/tmp/perlio.log perl -Di script ...
1141 and under Win32, the approximately equivalent:
1143 > set PERLIO_DEBUG=CON
1146 This functionality is disabled for setuid scripts, for scripts run
1147 with L</-T>, and for scripts run on a Perl built without C<-DDEBUGGING>
1153 A list of directories in which to look for Perl library
1154 files before looking in the standard library.
1155 If L</PERL5LIB> is defined, PERLLIB is not used.
1157 The PERLLIB environment variable is completely ignored when Perl
1158 is run in taint mode.
1163 The command used to load the debugger code. The default is:
1165 BEGIN { require "perl5db.pl" }
1167 The PERL5DB environment variable is only used when Perl is started with
1168 a bare L</-d> switch.
1170 =item PERL5DB_THREADED
1173 If set to a true value, indicates to the debugger that the code being
1174 debugged uses threads.
1176 =item PERL5SHELL (specific to the Win32 port)
1179 On Win32 ports only, may be set to an alternative shell that Perl must use
1180 internally for executing "backtick" commands or system(). Default is
1181 C<cmd.exe /x/d/c> on WindowsNT and C<command.com /c> on Windows95. The
1182 value is considered space-separated. Precede any character that
1183 needs to be protected, like a space or backslash, with another backslash.
1185 Note that Perl doesn't use COMSPEC for this purpose because
1186 COMSPEC has a high degree of variability among users, leading to
1187 portability concerns. Besides, Perl can use a shell that may not be
1188 fit for interactive use, and setting COMSPEC to such a shell may
1189 interfere with the proper functioning of other programs (which usually
1190 look in COMSPEC to find a shell fit for interactive use).
1192 Before Perl 5.10.0 and 5.8.8, PERL5SHELL was not taint checked
1193 when running external commands. It is recommended that
1194 you explicitly set (or delete) C<$ENV{PERL5SHELL}> when running
1195 in taint mode under Windows.
1197 =item PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
1198 X<PERL_ALLOW_NON_IFS_LSP>
1200 Set to 1 to allow the use of non-IFS compatible LSPs (Layered Service Providers).
1201 Perl normally searches for an IFS-compatible LSP because this is required
1202 for its emulation of Windows sockets as real filehandles. However, this may
1203 cause problems if you have a firewall such as I<McAfee Guardian>, which requires
1204 that all applications use its LSP but which is not IFS-compatible, because clearly
1205 Perl will normally avoid using such an LSP.
1207 Setting this environment variable to 1 means that Perl will simply use the
1208 first suitable LSP enumerated in the catalog, which keeps I<McAfee Guardian>
1209 happy--and in that particular case Perl still works too because I<McAfee
1210 Guardian>'s LSP actually plays other games which allow applications
1211 requiring IFS compatibility to work.
1213 =item PERL_DEBUG_MSTATS
1214 X<PERL_DEBUG_MSTATS>
1216 Relevant only if Perl is compiled with the C<malloc> included with the Perl
1217 distribution; that is, if C<perl -V:d_mymalloc> is "define".
1219 If set, this dumps out memory statistics after execution. If set
1220 to an integer greater than one, also dumps out memory statistics
1223 =item PERL_DESTRUCT_LEVEL
1224 X<PERL_DESTRUCT_LEVEL>
1226 Controls the behaviour of global destruction of objects and other
1227 references. See L<perlhacktips/PERL_DESTRUCT_LEVEL> for more information.
1229 =item PERL_DL_NONLAZY
1232 Set to C<"1"> to have Perl resolve I<all> undefined symbols when it loads
1233 a dynamic library. The default behaviour is to resolve symbols when
1234 they are used. Setting this variable is useful during testing of
1235 extensions, as it ensures that you get an error on misspelled function
1236 names even if the test suite doesn't call them.
1241 If using the C<use encoding> pragma without an explicit encoding name, the
1242 PERL_ENCODING environment variable is consulted for an encoding name.
1244 =item PERL_HASH_SEED
1247 (Since Perl 5.8.1, new semantics in Perl 5.18.0) Used to override
1248 the randomization of Perl's internal hash function. The value is expressed
1249 in hexadecimal, and may include a leading 0x. Truncated patterns
1250 are treated as though they are suffixed with sufficient 0's as required.
1252 If the option is provided, and C<PERL_PERTURB_KEYS> is NOT set, then
1253 a value of '0' implies C<PERL_PERTURB_KEYS=0> and any other value
1254 implies C<PERL_PERTURB_KEYS=2>.
1256 B<PLEASE NOTE: The hash seed is sensitive information>. Hashes are
1257 randomized to protect against local and remote attacks against Perl
1258 code. By manually setting a seed, this protection may be partially or
1261 See L<perlsec/"Algorithmic Complexity Attacks">, L</PERL_PERTURB_KEYS>, and
1262 L</PERL_HASH_SEED_DEBUG> for more information.
1264 =item PERL_PERTURB_KEYS
1265 X<PERL_PERTURB_KEYS>
1267 (Since Perl 5.18.0) Set to C<"0"> or C<"NO"> then traversing keys
1268 will be repeatable from run to run for the same C<PERL_HASH_SEED>.
1269 Insertion into a hash will not change the order, except to provide
1270 for more space in the hash. When combined with setting PERL_HASH_SEED
1271 this mode is as close to pre 5.18 behavior as you can get.
1273 When set to C<"1"> or C<"RANDOM"> then traversing keys will be randomized.
1274 Every time a hash is inserted into the key order will change in a random
1275 fashion. The order may not be repeatable in a following program run
1276 even if the PERL_HASH_SEED has been specified. This is the default
1279 When set to C<"2"> or C<"DETERMINISTIC"> then inserting keys into a hash
1280 will cause the key order to change, but in a way that is repeatable
1281 from program run to program run.
1283 B<NOTE:> Use of this option is considered insecure, and is intended only
1284 for debugging non-deterministic behavior in Perl's hash function. Do
1285 not use it in production.
1287 See L<perlsec/"Algorithmic Complexity Attacks"> and L</PERL_HASH_SEED>
1288 and L</PERL_HASH_SEED_DEBUG> for more information. You can get and set the
1289 key traversal mask for a specific hash by using the C<hash_traversal_mask()>
1290 function from L<Hash::Util>.
1292 =item PERL_HASH_SEED_DEBUG
1293 X<PERL_HASH_SEED_DEBUG>
1295 (Since Perl 5.8.1.) Set to C<"1"> to display (to STDERR) information
1296 about the hash function, seed, and what type of key traversal
1297 randomization is in effect at the beginning of execution. This, combined
1298 with L</PERL_HASH_SEED> and L</PERL_PERTURB_KEYS> is intended to aid in
1299 debugging nondeterministic behaviour caused by hash randomization.
1301 B<Note> that any information about the hash function, especially the hash
1302 seed is B<sensitive information>: by knowing it, one can craft a denial-of-service
1303 attack against Perl code, even remotely; see L<perlsec/"Algorithmic Complexity Attacks">
1304 for more information. B<Do not disclose the hash seed> to people who
1305 don't need to know it. See also L<C<hash_seed()>|Hash::Util/hash_seed> and
1306 L<C<hash_traversal_mask()>|Hash::Util/hash_traversal_mask>.
1308 An example output might be:
1310 HASH_FUNCTION = ONE_AT_A_TIME_HARD HASH_SEED = 0x652e9b9349a7a032 PERTURB_KEYS = 1 (RANDOM)
1315 If your Perl was configured with B<-Accflags=-DPERL_MEM_LOG>, setting
1316 the environment variable C<PERL_MEM_LOG> enables logging debug
1317 messages. The value has the form C<< <I<number>>[m][s][t] >>, where
1318 C<I<number>> is the file descriptor number you want to write to (2 is
1319 default), and the combination of letters specifies that you want
1320 information about (m)emory and/or (s)v, optionally with
1321 (t)imestamps. For example, C<PERL_MEM_LOG=1mst> logs all
1322 information to stdout. You can write to other opened file descriptors
1323 in a variety of ways:
1325 $ 3>foo3 PERL_MEM_LOG=3m perl ...
1327 =item PERL_ROOT (specific to the VMS port)
1330 A translation-concealed rooted logical name that contains Perl and the
1331 logical device for the @INC path on VMS only. Other logical names that
1332 affect Perl on VMS include PERLSHR, PERL_ENV_TABLES, and
1333 SYS$TIMEZONE_DIFFERENTIAL, but are optional and discussed further in
1334 L<perlvms> and in F<README.vms> in the Perl source distribution.
1339 Available in Perls 5.8.1 and later. If set to C<"unsafe">, the pre-Perl-5.8.0
1340 signal behaviour (which is immediate but unsafe) is restored. If set
1341 to C<safe>, then safe (but deferred) signals are used. See
1342 L<perlipc/"Deferred Signals (Safe Signals)">.
1347 Equivalent to the L<-C|/-C [numberE<sol>list]> command-line switch. Note
1348 that this is not a boolean variable. Setting this to C<"1"> is not the
1349 right way to "enable Unicode" (whatever that would mean). You can use
1350 C<"0"> to "disable Unicode", though (or alternatively unset PERL_UNICODE
1351 in your shell before starting Perl). See the description of the
1352 L<-C|/-C [numberE<sol>list]> switch for more information.
1354 =item PERL_USE_UNSAFE_INC
1355 X<PERL_USE_UNSAFE_INC>
1357 If perl has been configured to not have the current directory in
1358 L<C<@INC>|perlvar/@INC> by default, this variable can be set to C<"1">
1359 to reinstate it. It's primarily intended for use while building and
1360 testing modules that have not been updated to deal with "." not being in
1361 C<@INC> and should not be set in the environment for day-to-day use.
1363 =item SYS$LOGIN (specific to the VMS port)
1366 Used if chdir has no argument and L</HOME> and L</LOGDIR> are not set.
1368 =item PERL_INTERNAL_RAND_SEED
1369 X<PERL_INTERNAL_RAND_SEED>
1371 Set to a non-negative integer to seed the random number generator used
1372 internally by perl for a variety of purposes.
1374 Ignored if perl is run setuid or setgid. Used only for some limited
1375 startup randomization (hash keys) if C<-T> or C<-t> perl is started
1376 with tainting enabled.
1378 Perl may be built to ignore this variable.
1382 Perl also has environment variables that control how Perl handles data
1383 specific to particular natural languages; see L<perllocale>.
1385 Perl and its various modules and components, including its test frameworks,
1386 may sometimes make use of certain other environment variables. Some of
1387 these are specific to a particular platform. Please consult the
1388 appropriate module documentation and any documentation for your platform
1389 (like L<perlsolaris>, L<perllinux>, L<perlmacosx>, L<perlwin32>, etc) for
1390 variables peculiar to those specific situations.
1392 Perl makes all environment variables available to the program being
1393 executed, and passes these along to any child processes it starts.
1394 However, programs running setuid would do well to execute the following
1395 lines before doing anything else, just to keep people honest:
1397 $ENV{PATH} = "/bin:/usr/bin"; # or whatever you need
1398 $ENV{SHELL} = "/bin/sh" if exists $ENV{SHELL};
1399 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};
1401 =head1 ORDER OF APPLICATION
1403 Some options, in particular C<-I>, C<-M>, C<PERL5LIB> and C<PERL5OPT> can
1404 interact, and the order in which they are applied is important.
1406 Note that this section does not document what I<actually> happens inside the
1407 perl interpreter, it documents what I<effectively> happens.
1413 The effect of multiple C<-I> options is to C<unshift> them onto C<@INC>
1414 from right to left. So for example:
1418 will first prepend C<3> onto the front of C<@INC>, then prepend C<2>, and
1419 then prepend C<1>. The result is that C<@INC> begins with:
1425 Multiple C<-M> options are processed from left to right. So this:
1427 perl -Mlib=1 -Mlib=2 -Mlib=3
1429 will first use the L<lib> pragma to prepend C<1> to C<@INC>, then
1430 it will prepend C<2>, then it will prepend C<3>, resulting in an C<@INC>
1435 =item the PERL5LIB environment variable
1437 This contains a list of directories, separated by colons. The entire list
1438 is prepended to C<@INC> in one go. This:
1442 will result in an C<@INC> that begins with:
1446 =item combinations of -I, -M and PERL5LIB
1448 C<PERL5LIB> is applied first, then all the C<-I> arguments, then all the
1449 C<-M> arguments. This:
1451 PERL5LIB=e1:e2 perl -I i1 -Mlib=m1 -I i2 -Mlib=m2
1453 will result in an C<@INC> that begins with:
1455 qw(m2 m1 i1 i2 e1 e2)
1457 =item the PERL5OPT environment variable
1459 This contains a space separated list of switches. We only consider the
1460 effects of C<-M> and C<-I> in this section.
1462 After normal processing of C<-I> switches from the command line, all
1463 the C<-I> switches in C<PERL5OPT> are extracted. They are processed from
1464 left to right instead of from right to left. Also note that while
1465 whitespace is allowed between a C<-I> and its directory on the command
1466 line, it is not allowed in C<PERL5OPT>.
1468 After normal processing of C<-M> switches from the command line, all
1469 the C<-M> switches in C<PERL5OPT> are extracted. They are processed from
1470 left to right, I<i.e.> the same as those on the command line.
1472 An example may make this clearer:
1474 export PERL5OPT="-Mlib=optm1 -Iopti1 -Mlib=optm2 -Iopti2"
1475 export PERL5LIB=e1:e2
1476 perl -I i1 -Mlib=m1 -I i2 -Mlib=m2
1478 will result in an C<@INC> that begins with:
1497 =item Other complications
1499 There are some complications that are ignored in the examples above:
1503 =item arch and version subdirs
1505 All of C<-I>, C<PERL5LIB> and C<use lib> will also prepend arch and version
1506 subdirs if they are present
1508 =item sitecustomize.pl