1PERLRUN(1) Perl Programmers Reference Guide PERLRUN(1)
2
6 perlrun - how to execute the Perl interpreter
7
9 perl [ -sTtuUWX ] [ -hv ] [ -V[:configvar] ]
10 [ -cw ] [ -d[t][:debugger] ] [ -D[number/list] ]
11 [ -pna ] [ -Fpattern ] [ -l[octal] ] [ -0[octal/hexadecimal] ]
12 [ -Idir ] [ -m[-]module ] [ -M[-]'module...' ] [ -f ]
13 [ -C [number/list] ] [ -S ] [ -x[dir] ]
14 [ -i[extension] ]
15 [ [-e|-E] 'command' ] [ -- ] [ programfile ] [ argument ]...
16
18 The normal way to run a Perl program is by making it directly
19 executable, or else by passing the name of the source file as an
20 argument on the command line. (An interactive Perl environment is also
21 possible--see perldebug for details on how to do that.) Upon startup,
22 Perl looks for your program in one of the following places:
23 1. Specified line by line via -e or -E switches on the command line.
25 2. Contained in the file specified by the first filename on the
27 command line. (Note that systems supporting the "#!" notation
28 invoke interpreters this way. See "Location of Perl".)
29 3. Passed in implicitly via standard input. This works only if there
31 are no filename arguments--to pass arguments to a STDIN-read
32 program you must explicitly specify a "-" for the program name.
33 With methods 2 and 3, Perl starts parsing the input file from the
35 beginning, unless you've specified a "-x" switch, in which case it
36 scans for the first line starting with "#!" and containing the word
37 "perl", and starts there instead. This is useful for running a program
38 embedded in a larger message. (In this case you would indicate the end
39 of the program using the "__END__" token.)
40 The "#!" line is always examined for switches as the line is being
42 parsed. Thus, if you're on a machine that allows only one argument
43 with the "#!" line, or worse, doesn't even recognize the "#!" line, you
44 still can get consistent switch behaviour regardless of how Perl was
45 invoked, even if "-x" was used to find the beginning of the program.
46 Because historically some operating systems silently chopped off kernel
48 interpretation of the "#!" line after 32 characters, some switches may
49 be passed in on the command line, and some may not; you could even get
50 a "-" without its letter, if you're not careful. You probably want to
51 make sure that all your switches fall either before or after that
52 32-character boundary. Most switches don't actually care if they're
53 processed redundantly, but getting a "-" instead of a complete switch
54 could cause Perl to try to execute standard input instead of your
55 program. And a partial -I switch could also cause odd results.
56 Some switches do care if they are processed twice, for instance
58 combinations of -l and -0. Either put all the switches after the
59 32-character boundary (if applicable), or replace the use of -0digits
60 by "BEGIN{ $/ = "\0digits"; }".
61 Parsing of the "#!" switches starts wherever "perl" is mentioned in the
63 line. The sequences "-*" and "- " are specifically ignored so that you
64 could, if you were so inclined, say
65 #!/bin/sh
67 #! -*- perl -*- -p
68 eval 'exec perl -x -wS $0 ${1+"$@"}'
69 if 0;
70 to let Perl see the "-p" switch.
72 A similar trick involves the env program, if you have it.
74 #!/usr/bin/env perl
76 The examples above use a relative path to the perl interpreter, getting
78 whatever version is first in the user's path. If you want a specific
79 version of Perl, say, perl5.14.1, you should place that directly in the
80 "#!" line's path.
81 If the "#!" line does not contain the word "perl" nor the word "indir",
83 the program named after the "#!" is executed instead of the Perl
84 interpreter. This is slightly bizarre, but it helps people on machines
85 that don't do "#!", because they can tell a program that their SHELL is
86 /usr/bin/perl, and Perl will then dispatch the program to the correct
87 interpreter for them.
88 After locating your program, Perl compiles the entire program to an
90 internal form. If there are any compilation errors, execution of the
91 program is not attempted. (This is unlike the typical shell script,
92 which might run part-way through before finding a syntax error.)
93 If the program is syntactically correct, it is executed. If the
95 program runs off the end without hitting an exit() or die() operator,
96 an implicit exit(0) is provided to indicate successful completion.
97 #! and quoting on non-Unix systems
99 Unix's "#!" technique can be simulated on other systems:
100 OS/2
102 Put
103 extproc perl -S -your_switches
105 as the first line in "*.cmd" file ("-S" due to a bug in cmd.exe's
107 `extproc' handling).
108 MS-DOS
110 Create a batch file to run your program, and codify it in
111 "ALTERNATE_SHEBANG" (see the dosish.h file in the source
112 distribution for more information).
113 Win95/NT
115 The Win95/NT installation, when using the ActiveState installer for
116 Perl, will modify the Registry to associate the .pl extension with
117 the perl interpreter. If you install Perl by other means
118 (including building from the sources), you may have to modify the
119 Registry yourself. Note that this means you can no longer tell the
120 difference between an executable Perl program and a Perl library
121 file.
122 VMS Put
124 $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
126 $ exit++ + ++$status != 0 and $exit = $status = undef;
127 at the top of your program, where -mysw are any command line
129 switches you want to pass to Perl. You can now invoke the program
130 directly, by saying "perl program", or as a DCL procedure, by
131 saying @program (or implicitly via DCL$PATH by just using the name
132 of the program).
133 This incantation is a bit much to remember, but Perl will display
135 it for you if you say "perl "-V:startperl"".
136 Command-interpreters on non-Unix systems have rather different ideas on
138 quoting than Unix shells. You'll need to learn the special characters
139 in your command-interpreter ("*", "\" and """ are common) and how to
140 protect whitespace and these characters to run one-liners (see -e
141 below).
142 On some systems, you may have to change single-quotes to double ones,
144 which you must not do on Unix or Plan 9 systems. You might also have
145 to change a single % to a %%.
146 For example:
148 # Unix
150 perl -e 'print "Hello world\n"'
151 # MS-DOS, etc.
153 perl -e "print \"Hello world\n\""
154 # VMS
156 perl -e "print ""Hello world\n"""
157 The problem is that none of this is reliable: it depends on the command
159 and it is entirely possible neither works. If 4DOS were the command
160 shell, this would probably work better:
161 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
163 CMD.EXE in Windows NT slipped a lot of standard Unix functionality in
165 when nobody was looking, but just try to find documentation for its
166 quoting rules.
167 There is no general solution to all of this. It's just a mess.
169 Location of Perl
171 It may seem obvious to say, but Perl is useful only when users can
172 easily find it. When possible, it's good for both /usr/bin/perl and
173 /usr/local/bin/perl to be symlinks to the actual binary. If that can't
174 be done, system administrators are strongly encouraged to put (symlinks
175 to) perl and its accompanying utilities into a directory typically
176 found along a user's PATH, or in some other obvious and convenient
177 place.
178 In this documentation, "#!/usr/bin/perl" on the first line of the
180 program will stand in for whatever method works on your system. You
181 are advised to use a specific path if you care about a specific
182 version.
183 #!/usr/local/bin/perl5.14
185 or if you just want to be running at least version, place a statement
187 like this at the top of your program:
188 use 5.014;
190 Command Switches
192 As with all standard commands, a single-character switch may be
193 clustered with the following switch, if any.
194 #!/usr/bin/perl -spi.orig # same as -s -p -i.orig
196 A "--" signals the end of options and disables further option
198 processing. Any arguments after the "--" are treated as filenames and
199 arguments.
200 Switches include:
202 -0[octal/hexadecimal]
204 specifies the input record separator ($/) as an octal or
205 hexadecimal number. If there are no digits, the null character is
206 the separator. Other switches may precede or follow the digits.
207 For example, if you have a version of find which can print
208 filenames terminated by the null character, you can say this:
209 find . -name '*.orig' -print0 | perl -n0e unlink
211 The special value 00 will cause Perl to slurp files in paragraph
213 mode. Any value 0400 or above will cause Perl to slurp files
214 whole, but by convention the value 0777 is the one normally used
215 for this purpose.
216 You can also specify the separator character using hexadecimal
218 notation: -0xHHH..., where the "H" are valid hexadecimal digits.
219 Unlike the octal form, this one may be used to specify any Unicode
220 character, even those beyond 0xFF. So if you really want a record
221 separator of 0777, specify it as -0x1FF. (This means that you
222 cannot use the "-x" option with a directory name that consists of
223 hexadecimal digits, or else Perl will think you have specified a
224 hex number to -0.)
225 -a turns on autosplit mode when used with a "-n" or "-p". An
227 implicit split command to the @F array is done as the first thing
228 inside the implicit while loop produced by the "-n" or "-p".
229 perl -ane 'print pop(@F), "\n";'
231 is equivalent to
233 while (<>) {
235 @F = split(' ');
236 print pop(@F), "\n";
237 }
238 An alternate delimiter may be specified using -F.
240 -a implicitly sets "-n".
242 -C [number/list]
244 The -C flag controls some of the Perl Unicode features.
245 As of 5.8.1, the -C can be followed either by a number or a list
247 of option letters. The letters, their numeric values, and effects
248 are as follows; listing the letters is equal to summing the
249 numbers.
250 I 1 STDIN is assumed to be in UTF-8
252 O 2 STDOUT will be in UTF-8
253 E 4 STDERR will be in UTF-8
254 S 7 I + O + E
255 i 8 UTF-8 is the default PerlIO layer for input streams
256 o 16 UTF-8 is the default PerlIO layer for output streams
257 D 24 i + o
258 A 32 the @ARGV elements are expected to be strings encoded
259 in UTF-8
260 L 64 normally the "IOEioA" are unconditional, the L makes
261 them conditional on the locale environment variables
262 (the LC_ALL, LC_CTYPE, and LANG, in the order of
263 decreasing precedence) -- if the variables indicate
264 UTF-8, then the selected "IOEioA" are in effect
265 a 256 Set ${^UTF8CACHE} to -1, to run the UTF-8 caching
266 code in debugging mode.
267 For example, -COE and -C6 will both turn on UTF-8-ness on both
269 STDOUT and STDERR. Repeating letters is just redundant, not
270 cumulative nor toggling.
271 The "io" options mean that any subsequent open() (or similar I/O
273 operations) in main program scope will have the ":utf8" PerlIO
274 layer implicitly applied to them, in other words, UTF-8 is
275 expected from any input stream, and UTF-8 is produced to any
276 output stream. This is just the default set via "${^OPEN}", with
277 explicit layers in open() and with binmode() one can manipulate
278 streams as usual. This has no effect on code run in modules.
279 -C on its own (not followed by any number or option list), or the
281 empty string "" for the "PERL_UNICODE" environment variable, has
282 the same effect as -CSDL. In other words, the standard I/O
283 handles and the default "open()" layer are UTF-8-fied but only if
284 the locale environment variables indicate a UTF-8 locale. This
285 behaviour follows the implicit (and problematic) UTF-8 behaviour
286 of Perl 5.8.0. (See "UTF-8 no longer default under UTF-8 locales"
287 in perl581delta.)
288 You can use -C0 (or "0" for "PERL_UNICODE") to explicitly disable
290 all the above Unicode features.
291 The read-only magic variable "${^UNICODE}" reflects the numeric
293 value of this setting. This variable is set during Perl startup
294 and is thereafter read-only. If you want runtime effects, use the
295 three-arg open() (see "open" in perlfunc), the two-arg binmode()
296 (see "binmode" in perlfunc), and the "open" pragma (see open).
297 (In Perls earlier than 5.8.1 the -C switch was a Win32-only switch
299 that enabled the use of Unicode-aware "wide system call" Win32
300 APIs. This feature was practically unused, however, and the
301 command line switch was therefore "recycled".)
302 Note: Since perl 5.10.1, if the -C option is used on the "#!"
304 line, it must be specified on the command line as well, since the
305 standard streams are already set up at this point in the execution
306 of the perl interpreter. You can also use binmode() to set the
307 encoding of an I/O stream.
308 -c causes Perl to check the syntax of the program and then exit
310 without executing it. Actually, it will execute any "BEGIN",
311 "UNITCHECK", or "CHECK" blocks and any "use" statements: these are
312 considered as occurring outside the execution of your program.
313 "INIT" and "END" blocks, however, will be skipped.
314 -d
316 -dt runs the program under the Perl debugger. See perldebug. If t is
317 specified, it indicates to the debugger that threads will be used
318 in the code being debugged.
319 -d:MOD[=bar,baz]
321 -dt:MOD[=bar,baz]
322 runs the program under the control of a debugging, profiling, or
323 tracing module installed as "Devel::MOD". E.g., -d:DProf executes
324 the program using the "Devel::DProf" profiler. As with the -M
325 flag, options may be passed to the "Devel::MOD" package where they
326 will be received and interpreted by the "Devel::MOD::import"
327 routine. Again, like -M, use --d:-MOD to call
328 "Devel::MOD::unimport" instead of import. The comma-separated
329 list of options must follow a "=" character. If t is specified,
330 it indicates to the debugger that threads will be used in the code
331 being debugged. See perldebug.
332 -Dletters
334 -Dnumber
335 sets debugging flags. This switch is enabled only if your perl
336 binary has been built with debugging enabled: normal production
337 perls won't have been.
338 For example, to watch how perl executes your program, use -Dtls.
340 Another nice value is -Dx, which lists your compiled syntax tree,
341 and -Dr displays compiled regular expressions; the format of the
342 output is explained in perldebguts.
343 As an alternative, specify a number instead of list of letters
345 (e.g., -D14 is equivalent to -Dtls):
346 1 p Tokenizing and parsing (with v, displays parse
348 stack)
349 2 s Stack snapshots (with v, displays all stacks)
350 4 l Context (loop) stack processing
351 8 t Trace execution
352 16 o Method and overloading resolution
353 32 c String/numeric conversions
354 64 P Print profiling info, source file input state
355 128 m Memory and SV allocation
356 256 f Format processing
357 512 r Regular expression parsing and execution
358 1024 x Syntax tree dump
359 2048 u Tainting checks
360 4096 U Unofficial, User hacking (reserved for private,
361 unreleased use)
362 16384 X Scratchpad allocation
363 32768 D Cleaning up
364 65536 S Op slab allocation
365 131072 T Tokenizing
366 262144 R Include reference counts of dumped variables
367 (eg when using -Ds)
368 524288 J show s,t,P-debug (don't Jump over) on opcodes within
369 package DB
370 1048576 v Verbose: use in conjunction with other flags to
371 increase the verbosity of the output. Is a no-op on
372 many of the other flags
373 2097152 C Copy On Write
374 4194304 A Consistency checks on internal structures
375 8388608 q quiet - currently only suppresses the "EXECUTING"
376 message
377 16777216 M trace smart match resolution
378 33554432 B dump suBroutine definitions, including special
379 Blocks like BEGIN
380 67108864 L trace Locale-related info; what gets output is very
381 subject to change
382 134217728 i trace PerlIO layer processing. Set PERLIO_DEBUG to
383 the filename to trace to.
384 268435456 y trace y///, tr/// compilation and execution
385 All these flags require -DDEBUGGING when you compile the Perl
387 executable (but see ":opd" in Devel::Peek or "'debug' mode" in re
388 which may change this). See the INSTALL file in the Perl source
389 distribution for how to do this.
390 If you're just trying to get a print out of each line of Perl code
392 as it executes, the way that "sh -x" provides for shell scripts,
393 you can't use Perl's -D switch. Instead do this
394 # If you have "env" utility
396 env PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
397 # Bourne shell syntax
399 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
400 # csh syntax
402 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
403 See perldebug for details and variations.
405 -e commandline
407 may be used to enter one line of program. If -e is given, Perl
408 will not look for a filename in the argument list. Multiple -e
409 commands may be given to build up a multi-line script. Make sure
410 to use semicolons where you would in a normal program.
411 -E commandline
413 behaves just like -e, except that it implicitly enables all
414 optional features (in the main compilation unit). See feature.
415 -f Disable executing $Config{sitelib}/sitecustomize.pl at startup.
417 Perl can be built so that it by default will try to execute
419 $Config{sitelib}/sitecustomize.pl at startup (in a BEGIN block).
420 This is a hook that allows the sysadmin to customize how Perl
421 behaves. It can for instance be used to add entries to the @INC
422 array to make Perl find modules in non-standard locations.
423 Perl actually inserts the following code:
425 BEGIN {
427 do { local $!; -f "$Config{sitelib}/sitecustomize.pl"; }
428 && do "$Config{sitelib}/sitecustomize.pl";
429 }
430 Since it is an actual "do" (not a "require"), sitecustomize.pl
432 doesn't need to return a true value. The code is run in package
433 "main", in its own lexical scope. However, if the script dies, $@
434 will not be set.
435 The value of $Config{sitelib} is also determined in C code and not
437 read from "Config.pm", which is not loaded.
438 The code is executed very early. For example, any changes made to
440 @INC will show up in the output of `perl -V`. Of course, "END"
441 blocks will be likewise executed very late.
442 To determine at runtime if this capability has been compiled in
444 your perl, you can check the value of $Config{usesitecustomize}.
445 -Fpattern
447 specifies the pattern to split on for "-a". The pattern may be
448 surrounded by "//", "", or '', otherwise it will be put in single
449 quotes. You can't use literal whitespace or NUL characters in the
450 pattern.
451 -F implicitly sets both "-a" and "-n".
453 -h prints a summary of the options.
455 -i[extension]
457 specifies that files processed by the "<>" construct are to be
458 edited in-place. It does this by renaming the input file, opening
459 the output file by the original name, and selecting that output
460 file as the default for print() statements. The extension, if
461 supplied, is used to modify the name of the old file to make a
462 backup copy, following these rules:
463 If no extension is supplied, and your system supports it, the
465 original file is kept open without a name while the output is
466 redirected to a new file with the original filename. When perl
467 exits, cleanly or not, the original file is unlinked.
468 If the extension doesn't contain a "*", then it is appended to the
470 end of the current filename as a suffix. If the extension does
471 contain one or more "*" characters, then each "*" is replaced with
472 the current filename. In Perl terms, you could think of this as:
473 ($backup = $extension) =~ s/\*/$file_name/g;
475 This allows you to add a prefix to the backup file, instead of (or
477 in addition to) a suffix:
478 $ perl -pi'orig_*' -e 's/bar/baz/' fileA # backup to
480 # 'orig_fileA'
481 Or even to place backup copies of the original files into another
483 directory (provided the directory already exists):
484 $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to
486 # 'old/fileA.orig'
487 These sets of one-liners are equivalent:
489 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
491 $ perl -pi'*' -e 's/bar/baz/' fileA # overwrite current file
492 $ perl -pi'.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
494 $ perl -pi'*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
495 From the shell, saying
497 $ perl -p -i.orig -e "s/foo/bar/; ... "
499 is the same as using the program:
501 #!/usr/bin/perl -pi.orig
503 s/foo/bar/;
504 which is equivalent to
506 #!/usr/bin/perl
508 $extension = '.orig';
509 LINE: while (<>) {
510 if ($ARGV ne $oldargv) {
511 if ($extension !~ /\*/) {
512 $backup = $ARGV . $extension;
513 }
514 else {
515 ($backup = $extension) =~ s/\*/$ARGV/g;
516 }
517 rename($ARGV, $backup);
518 open(ARGVOUT, ">$ARGV");
519 select(ARGVOUT);
520 $oldargv = $ARGV;
521 }
522 s/foo/bar/;
523 }
524 continue {
525 print; # this prints to original filename
526 }
527 select(STDOUT);
528 except that the -i form doesn't need to compare $ARGV to $oldargv
530 to know when the filename has changed. It does, however, use
531 ARGVOUT for the selected filehandle. Note that STDOUT is restored
532 as the default output filehandle after the loop.
533 As shown above, Perl creates the backup file whether or not any
535 output is actually changed. So this is just a fancy way to copy
536 files:
537 $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
539 or
540 $ perl -p -i'.orig' -e 1 file1 file2 file3...
541 You can use "eof" without parentheses to locate the end of each
543 input file, in case you want to append to each file, or reset line
544 numbering (see example in "eof" in perlfunc).
545 If, for a given file, Perl is unable to create the backup file as
547 specified in the extension then it will skip that file and
548 continue on with the next one (if it exists).
549 For a discussion of issues surrounding file permissions and -i,
551 see "Why does Perl let me delete read-only files? Why does -i
552 clobber protected files? Isn't this a bug in Perl?" in perlfaq5.
553 You cannot use -i to create directories or to strip extensions
555 from files.
556 Perl does not expand "~" in filenames, which is good, since some
558 folks use it for their backup files:
559 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
561 Note that because -i renames or deletes the original file before
563 creating a new file of the same name, Unix-style soft and hard
564 links will not be preserved.
565 Finally, the -i switch does not impede execution when no files are
567 given on the command line. In this case, no backup is made (the
568 original file cannot, of course, be determined) and processing
569 proceeds from STDIN to STDOUT as might be expected.
570 -Idirectory
572 Directories specified by -I are prepended to the search path for
573 modules (@INC).
574 -l[octnum]
576 enables automatic line-ending processing. It has two separate
577 effects. First, it automatically chomps $/ (the input record
578 separator) when used with "-n" or "-p". Second, it assigns "$\"
579 (the output record separator) to have the value of octnum so that
580 any print statements will have that separator added back on. If
581 octnum is omitted, sets "$\" to the current value of $/. For
582 instance, to trim lines to 80 columns:
583 perl -lpe 'substr($_, 80) = ""'
585 Note that the assignment "$\ = $/" is done when the switch is
587 processed, so the input record separator can be different than the
588 output record separator if the -l switch is followed by a -0
589 switch:
590 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
592 This sets "$\" to newline and then sets $/ to the null character.
594 -m[-]module
596 -M[-]module
597 -M[-]'module ...'
598 -[mM][-]module=arg[,arg]...
599 -mmodule executes "use" module "();" before executing your
600 program. This loads the module, but does not call its "import"
601 method, so does not import subroutines and does not give effect to
602 a pragma.
603 -Mmodule executes "use" module ";" before executing your program.
605 This loads the module and calls its "import" method, causing the
606 module to have its default effect, typically importing subroutines
607 or giving effect to a pragma. You can use quotes to add extra
608 code after the module name, e.g., '-MMODULE qw(foo bar)'.
609 If the first character after the -M or -m is a dash (-) then the
611 'use' is replaced with 'no'. This makes no difference for -m.
612 A little builtin syntactic sugar means you can also say
614 -mMODULE=foo,bar or -MMODULE=foo,bar as a shortcut for '-MMODULE
615 qw(foo bar)'. This avoids the need to use quotes when importing
616 symbols. The actual code generated by -MMODULE=foo,bar is "use
617 module split(/,/,q{foo,bar})". Note that the "=" form removes the
618 distinction between -m and -M; that is, -mMODULE=foo,bar is the
619 same as -MMODULE=foo,bar.
620 A consequence of the "split" formulation is that -MMODULE=number
622 never does a version check, unless "MODULE::import()" itself is
623 set up to do a version check, which could happen for example if
624 MODULE inherits from Exporter.
625 -n causes Perl to assume the following loop around your program,
627 which makes it iterate over filename arguments somewhat like sed
628 -n or awk:
629 LINE:
631 while (<>) {
632 ... # your program goes here
633 }
634 Note that the lines are not printed by default. See "-p" to have
636 lines printed. If a file named by an argument cannot be opened
637 for some reason, Perl warns you about it and moves on to the next
638 file.
639 Also note that "<>" passes command line arguments to "open" in
641 perlfunc, which doesn't necessarily interpret them as file names.
642 See perlop for possible security implications.
643 Here is an efficient way to delete all files that haven't been
645 modified for at least a week:
646 find . -mtime +7 -print | perl -nle unlink
648 This is faster than using the -exec switch of find because you
650 don't have to start a process on every filename found (but it's
651 not faster than using the -delete switch available in newer
652 versions of find. It does suffer from the bug of mishandling
653 newlines in pathnames, which you can fix if you follow the example
654 under -0.
655 "BEGIN" and "END" blocks may be used to capture control before or
657 after the implicit program loop, just as in awk.
658 -p causes Perl to assume the following loop around your program,
660 which makes it iterate over filename arguments somewhat like sed:
661 LINE:
663 while (<>) {
664 ... # your program goes here
665 } continue {
666 print or die "-p destination: $!\n";
667 }
668 If a file named by an argument cannot be opened for some reason,
670 Perl warns you about it, and moves on to the next file. Note that
671 the lines are printed automatically. An error occurring during
672 printing is treated as fatal. To suppress printing use the "-n"
673 switch. A -p overrides a -n switch.
674 "BEGIN" and "END" blocks may be used to capture control before or
676 after the implicit loop, just as in awk.
677 -s enables rudimentary switch parsing for switches on the command
679 line after the program name but before any filename arguments (or
680 before an argument of --). Any switch found there is removed from
681 @ARGV and sets the corresponding variable in the Perl program.
682 The following program prints "1" if the program is invoked with a
683 -xyz switch, and "abc" if it is invoked with -xyz=abc.
684 #!/usr/bin/perl -s
686 if ($xyz) { print "$xyz\n" }
687 Do note that a switch like --help creates the variable "${-help}",
689 which is not compliant with "use strict "refs"". Also, when using
690 this option on a script with warnings enabled you may get a lot of
691 spurious "used only once" warnings.
692 -S makes Perl use the "PATH" environment variable to search for the
694 program unless the name of the program contains path separators.
695 On some platforms, this also makes Perl append suffixes to the
697 filename while searching for it. For example, on Win32 platforms,
698 the ".bat" and ".cmd" suffixes are appended if a lookup for the
699 original name fails, and if the name does not already end in one
700 of those suffixes. If your Perl was compiled with "DEBUGGING"
701 turned on, using the -Dp switch to Perl shows how the search
702 progresses.
703 Typically this is used to emulate "#!" startup on platforms that
705 don't support "#!". It's also convenient when debugging a script
706 that uses "#!", and is thus normally found by the shell's $PATH
707 search mechanism.
708 This example works on many platforms that have a shell compatible
710 with Bourne shell:
711 #!/usr/bin/perl
713 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
714 if 0; # ^ Run only under a shell
715 The system ignores the first line and feeds the program to
717 /bin/sh, which proceeds to try to execute the Perl program as a
718 shell script. The shell executes the second line as a normal
719 shell command, and thus starts up the Perl interpreter. On some
720 systems $0 doesn't always contain the full pathname, so the "-S"
721 tells Perl to search for the program if necessary. After Perl
722 locates the program, it parses the lines and ignores them because
723 the check 'if 0' is never true. If the program will be
724 interpreted by csh, you will need to replace "${1+"$@"}" with $*,
725 even though that doesn't understand embedded spaces (and such) in
726 the argument list. To start up sh rather than csh, some systems
727 may have to replace the "#!" line with a line containing just a
728 colon, which will be politely ignored by Perl. Other systems
729 can't control that, and need a totally devious construct that will
730 work under any of csh, sh, or Perl, such as the following:
731 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
733 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
734 if 0; # ^ Run only under a shell
735 If the filename supplied contains directory separators (and so is
737 an absolute or relative pathname), and if that file is not found,
738 platforms that append file extensions will do so and try to look
739 for the file with those extensions added, one by one.
740 On DOS-like platforms, if the program does not contain directory
742 separators, it will first be searched for in the current directory
743 before being searched for on the PATH. On Unix platforms, the
744 program will be searched for strictly on the PATH.
745 -t Like "-T", but taint checks will issue warnings rather than fatal
747 errors. These warnings can now be controlled normally with "no
748 warnings qw(taint)".
749 Note: This is not a substitute for "-T"! This is meant to be used
751 only as a temporary development aid while securing legacy code:
752 for real production code and for new secure code written from
753 scratch, always use the real "-T".
754 -T turns on "taint" so you can test them. Ordinarily these checks
756 are done only when running setuid or setgid. It's a good idea to
757 turn them on explicitly for programs that run on behalf of someone
758 else whom you might not necessarily trust, such as CGI programs or
759 any internet servers you might write in Perl. See perlsec for
760 details. For security reasons, this option must be seen by Perl
761 quite early; usually this means it must appear early on the
762 command line or in the "#!" line for systems which support that
763 construct.
764 -u This switch causes Perl to dump core after compiling your program.
766 You can then in theory take this core dump and turn it into an
767 executable file by using the undump program (not supplied). This
768 speeds startup at the expense of some disk space (which you can
769 minimize by stripping the executable). (Still, a "hello world"
770 executable comes out to about 200K on my machine.) If you want to
771 execute a portion of your program before dumping, use the
772 "CORE::dump()" function instead. Note: availability of undump is
773 platform specific and may not be available for a specific port of
774 Perl.
775 -U allows Perl to do unsafe operations. Currently the only "unsafe"
777 operations are attempting to unlink directories while running as
778 superuser and running setuid programs with fatal taint checks
779 turned into warnings. Note that warnings must be enabled along
780 with this option to actually generate the taint-check warnings.
781 -v prints the version and patchlevel of your perl executable.
783 -V prints summary of the major perl configuration values and the
785 current values of @INC.
786 -V:configvar
788 Prints to STDOUT the value of the named configuration variable(s),
789 with multiples when your "configvar" argument looks like a regex
790 (has non-letters). For example:
791 $ perl -V:libc
793 libc='/lib/libc-2.2.4.so';
794 $ perl -V:lib.
795 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
796 libc='/lib/libc-2.2.4.so';
797 $ perl -V:lib.*
798 libpth='/usr/local/lib /lib /usr/lib';
799 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
800 lib_ext='.a';
801 libc='/lib/libc-2.2.4.so';
802 libperl='libperl.a';
803 ....
804 Additionally, extra colons can be used to control formatting. A
806 trailing colon suppresses the linefeed and terminator ";",
807 allowing you to embed queries into shell commands. (mnemonic:
808 PATH separator ":".)
809 $ echo "compression-vars: " `perl -V:z.*: ` " are here !"
811 compression-vars: zcat='' zip='zip' are here !
812 A leading colon removes the "name=" part of the response, this
814 allows you to map to the name you need. (mnemonic: empty label)
815 $ echo "goodvfork="`./perl -Ilib -V::usevfork`
817 goodvfork=false;
818 Leading and trailing colons can be used together if you need
820 positional parameter values without the names. Note that in the
821 case below, the "PERL_API" params are returned in alphabetical
822 order.
823 $ echo building_on `perl -V::osname: -V::PERL_API_.*:` now
825 building_on 'linux' '5' '1' '9' now
826 -w prints warnings about dubious constructs, such as variable names
828 mentioned only once and scalar variables used before being set;
829 redefined subroutines; references to undefined filehandles;
830 filehandles opened read-only that you are attempting to write on;
831 values used as a number that don't look like numbers; using an
832 array as though it were a scalar; if your subroutines recurse more
833 than 100 deep; and innumerable other things.
834 This switch really just enables the global $^W variable; normally,
836 the lexically scoped "use warnings" pragma is preferred. You can
837 disable or promote into fatal errors specific warnings using
838 "__WARN__" hooks, as described in perlvar and "warn" in perlfunc.
839 See also perldiag and perltrap. A fine-grained warning facility
840 is also available if you want to manipulate entire classes of
841 warnings; see warnings.
842 -W Enables all warnings regardless of "no warnings" or $^W. See
844 warnings.
845 -X Disables all warnings regardless of "use warnings" or $^W. See
847 warnings.
848 Forbidden in "PERL5OPT".
850 -x
852 -xdirectory
853 tells Perl that the program is embedded in a larger chunk of
854 unrelated text, such as in a mail message. Leading garbage will
855 be discarded until the first line that starts with "#!" and
856 contains the string "perl". Any meaningful switches on that line
857 will be applied.
858 All references to line numbers by the program (warnings, errors,
860 ...) will treat the "#!" line as the first line. Thus a warning
861 on the 2nd line of the program, which is on the 100th line in the
862 file will be reported as line 2, not as line 100. This can be
863 overridden by using the "#line" directive. (See "Plain Old
864 Comments (Not!)" in perlsyn)
865 If a directory name is specified, Perl will switch to that
867 directory before running the program. The -x switch controls only
868 the disposal of leading garbage. The program must be terminated
869 with "__END__" if there is trailing garbage to be ignored; the
870 program can process any or all of the trailing garbage via the
871 "DATA" filehandle if desired.
872 The directory, if specified, must appear immediately following the
874 -x with no intervening whitespace.
875
877 HOME Used if "chdir" has no argument.
878 LOGDIR Used if "chdir" has no argument and "HOME" is not set.
880 PATH Used in executing subprocesses, and in finding the program
882 if "-S" is used.
883 PERL5LIB A list of directories in which to look for Perl library
885 files before looking in the standard library. Any
886 architecture-specific and version-specific directories,
887 such as version/archname/, version/, or archname/ under the
888 specified locations are automatically included if they
889 exist, with this lookup done at interpreter startup time.
890 In addition, any directories matching the entries in
891 $Config{inc_version_list} are added. (These typically
892 would be for older compatible perl versions installed in
893 the same directory tree.)
894 If PERL5LIB is not defined, "PERLLIB" is used. Directories
896 are separated (like in PATH) by a colon on Unixish
897 platforms and by a semicolon on Windows (the proper path
898 separator being given by the command "perl -V:path_sep").
899 When running taint checks, either because the program was
901 running setuid or setgid, or the "-T" or "-t" switch was
902 specified, neither PERL5LIB nor "PERLLIB" is consulted. The
903 program should instead say:
904 use lib "/my/directory";
906 PERL5OPT Command-line options (switches). Switches in this variable
908 are treated as if they were on every Perl command line.
909 Only the -[CDIMTUWdmtw] switches are allowed. When running
910 taint checks (either because the program was running setuid
911 or setgid, or because the "-T" or "-t" switch was used),
912 this variable is ignored. If PERL5OPT begins with -T,
913 tainting will be enabled and subsequent options ignored.
914 If PERL5OPT begins with -t, tainting will be enabled, a
915 writable dot removed from @INC, and subsequent options
916 honored.
917 PERLIO A space (or colon) separated list of PerlIO layers. If perl
919 is built to use PerlIO system for IO (the default) these
920 layers affect Perl's IO.
921 It is conventional to start layer names with a colon (for
923 example, ":perlio") to emphasize their similarity to
924 variable "attributes". But the code that parses layer
925 specification strings, which is also used to decode the
926 PERLIO environment variable, treats the colon as a
927 separator.
928 An unset or empty PERLIO is equivalent to the default set
930 of layers for your platform; for example, ":unix:perlio" on
931 Unix-like systems and ":unix:crlf" on Windows and other
932 DOS-like systems.
933 The list becomes the default for all Perl's IO.
935 Consequently only built-in layers can appear in this list,
936 as external layers (such as ":encoding()") need IO in order
937 to load them! See "open pragma" for how to add external
938 encodings as defaults.
939 Layers it makes sense to include in the PERLIO environment
941 variable are briefly summarized below. For more details see
942 PerlIO.
943 :crlf A layer which does CRLF to "\n" translation
945 distinguishing "text" and "binary" files in the
946 manner of MS-DOS and similar operating systems, and
947 also provides buffering similar to ":perlio" on
948 these architectures.
949 :perlio This is a re-implementation of stdio-like buffering
951 written as a PerlIO layer. As such it will call
952 whatever layer is below it for its operations,
953 typically ":unix".
954 :stdio This layer provides a PerlIO interface by wrapping
956 system's ANSI C "stdio" library calls. The layer
957 provides both buffering and IO. Note that the
958 ":stdio" layer does not do CRLF translation even if
959 that is the platform's normal behaviour. You will
960 need a ":crlf" layer above it to do that.
961 :unix Low-level layer that calls "read", "write",
963 "lseek", etc.
964 :win32 On Win32 platforms this experimental layer uses
966 native "handle" IO rather than a Unix-like numeric
967 file descriptor layer. Known to be buggy in this
968 release (5.30).
969 The default set of layers should give acceptable results on
971 all platforms.
972 For Unix platforms that will be the equivalent of
974 ":unix:perlio" or ":stdio". Configure is set up to prefer
975 the ":stdio" implementation if the system's library
976 provides for fast access to the buffer (not common on
977 modern architectures); otherwise, it uses the
978 ":unix:perlio" implementation.
979 On Win32 the default in this release (5.30) is
981 ":unix:crlf". Win32's ":stdio" has a number of
982 bugs/mis-features for Perl IO which are somewhat depending
983 on the version and vendor of the C compiler. Using our own
984 ":crlf" layer as the buffer avoids those issues and makes
985 things more uniform.
986 This release (5.30) uses ":unix" as the bottom layer on
988 Win32, and so still uses the C compiler's numeric file
989 descriptor routines. There is an experimental native
990 ":win32" layer, which is expected to be enhanced and may
991 eventually become the default under Win32.
992 The PERLIO environment variable is completely ignored when
994 Perl is run in taint mode.
995 PERLIO_DEBUG
997 If set to the name of a file or device when Perl is run
998 with the -Di command-line switch, the logging of certain
999 operations of the PerlIO subsystem will be redirected to
1000 the specified file rather than going to stderr, which is
1001 the default. The file is opened in append mode. Typical
1002 uses are in Unix:
1003 % env PERLIO_DEBUG=/tmp/perlio.log perl -Di script ...
1005 and under Win32, the approximately equivalent:
1007 > set PERLIO_DEBUG=CON
1009 perl -Di script ...
1010 This functionality is disabled for setuid scripts, for
1012 scripts run with "-T", and for scripts run on a Perl built
1013 without "-DDEBUGGING" support.
1014 PERLLIB A list of directories in which to look for Perl library
1016 files before looking in the standard library. If
1017 "PERL5LIB" is defined, PERLLIB is not used.
1018 The PERLLIB environment variable is completely ignored when
1020 Perl is run in taint mode.
1021 PERL5DB The command used to load the debugger code. The default
1023 is:
1024 BEGIN { require "perl5db.pl" }
1026 The PERL5DB environment variable is only used when Perl is
1028 started with a bare "-d" switch.
1029 PERL5DB_THREADED
1031 If set to a true value, indicates to the debugger that the
1032 code being debugged uses threads.
1033 PERL5SHELL (specific to the Win32 port)
1035 On Win32 ports only, may be set to an alternative shell
1036 that Perl must use internally for executing "backtick"
1037 commands or system(). Default is "cmd.exe /x/d/c" on
1038 WindowsNT and "command.com /c" on Windows95. The value is
1039 considered space-separated. Precede any character that
1040 needs to be protected, like a space or backslash, with
1041 another backslash.
1042 Note that Perl doesn't use COMSPEC for this purpose because
1044 COMSPEC has a high degree of variability among users,
1045 leading to portability concerns. Besides, Perl can use a
1046 shell that may not be fit for interactive use, and setting
1047 COMSPEC to such a shell may interfere with the proper
1048 functioning of other programs (which usually look in
1049 COMSPEC to find a shell fit for interactive use).
1050 Before Perl 5.10.0 and 5.8.8, PERL5SHELL was not taint
1052 checked when running external commands. It is recommended
1053 that you explicitly set (or delete) $ENV{PERL5SHELL} when
1054 running in taint mode under Windows.
1055 PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
1057 Set to 1 to allow the use of non-IFS compatible LSPs
1058 (Layered Service Providers). Perl normally searches for an
1059 IFS-compatible LSP because this is required for its
1060 emulation of Windows sockets as real filehandles. However,
1061 this may cause problems if you have a firewall such as
1062 McAfee Guardian, which requires that all applications use
1063 its LSP but which is not IFS-compatible, because clearly
1064 Perl will normally avoid using such an LSP.
1065 Setting this environment variable to 1 means that Perl will
1067 simply use the first suitable LSP enumerated in the
1068 catalog, which keeps McAfee Guardian happy--and in that
1069 particular case Perl still works too because McAfee
1070 Guardian's LSP actually plays other games which allow
1071 applications requiring IFS compatibility to work.
1072 PERL_DEBUG_MSTATS
1074 Relevant only if Perl is compiled with the "malloc"
1075 included with the Perl distribution; that is, if "perl
1076 -V:d_mymalloc" is "define".
1077 If set, this dumps out memory statistics after execution.
1079 If set to an integer greater than one, also dumps out
1080 memory statistics after compilation.
1081 PERL_DESTRUCT_LEVEL
1083 Controls the behaviour of global destruction of objects and
1084 other references. See "PERL_DESTRUCT_LEVEL" in
1085 perlhacktips for more information.
1086 PERL_DL_NONLAZY
1088 Set to "1" to have Perl resolve all undefined symbols when
1089 it loads a dynamic library. The default behaviour is to
1090 resolve symbols when they are used. Setting this variable
1091 is useful during testing of extensions, as it ensures that
1092 you get an error on misspelled function names even if the
1093 test suite doesn't call them.
1094 PERL_ENCODING
1096 If using the "use encoding" pragma without an explicit
1097 encoding name, the PERL_ENCODING environment variable is
1098 consulted for an encoding name.
1099 PERL_HASH_SEED
1101 (Since Perl 5.8.1, new semantics in Perl 5.18.0) Used to
1102 override the randomization of Perl's internal hash
1103 function. The value is expressed in hexadecimal, and may
1104 include a leading 0x. Truncated patterns are treated as
1105 though they are suffixed with sufficient 0's as required.
1106 If the option is provided, and "PERL_PERTURB_KEYS" is NOT
1108 set, then a value of '0' implies "PERL_PERTURB_KEYS=0" and
1109 any other value implies "PERL_PERTURB_KEYS=2".
1110 PLEASE NOTE: The hash seed is sensitive information. Hashes
1112 are randomized to protect against local and remote attacks
1113 against Perl code. By manually setting a seed, this
1114 protection may be partially or completely lost.
1115 See "Algorithmic Complexity Attacks" in perlsec,
1117 "PERL_PERTURB_KEYS", and "PERL_HASH_SEED_DEBUG" for more
1118 information.
1119 PERL_PERTURB_KEYS
1121 (Since Perl 5.18.0) Set to "0" or "NO" then traversing
1122 keys will be repeatable from run to run for the same
1123 "PERL_HASH_SEED". Insertion into a hash will not change
1124 the order, except to provide for more space in the hash.
1125 When combined with setting PERL_HASH_SEED this mode is as
1126 close to pre 5.18 behavior as you can get.
1127 When set to "1" or "RANDOM" then traversing keys will be
1129 randomized. Every time a hash is inserted into the key
1130 order will change in a random fashion. The order may not be
1131 repeatable in a following program run even if the
1132 PERL_HASH_SEED has been specified. This is the default mode
1133 for perl.
1134 When set to "2" or "DETERMINISTIC" then inserting keys into
1136 a hash will cause the key order to change, but in a way
1137 that is repeatable from program run to program run.
1138 NOTE: Use of this option is considered insecure, and is
1140 intended only for debugging non-deterministic behavior in
1141 Perl's hash function. Do not use it in production.
1142 See "Algorithmic Complexity Attacks" in perlsec and
1144 "PERL_HASH_SEED" and "PERL_HASH_SEED_DEBUG" for more
1145 information. You can get and set the key traversal mask for
1146 a specific hash by using the "hash_traversal_mask()"
1147 function from Hash::Util.
1148 PERL_HASH_SEED_DEBUG
1150 (Since Perl 5.8.1.) Set to "1" to display (to STDERR)
1151 information about the hash function, seed, and what type of
1152 key traversal randomization is in effect at the beginning
1153 of execution. This, combined with "PERL_HASH_SEED" and
1154 "PERL_PERTURB_KEYS" is intended to aid in debugging
1155 nondeterministic behaviour caused by hash randomization.
1156 Note that any information about the hash function,
1158 especially the hash seed is sensitive information: by
1159 knowing it, one can craft a denial-of-service attack
1160 against Perl code, even remotely; see "Algorithmic
1161 Complexity Attacks" in perlsec for more information. Do not
1162 disclose the hash seed to people who don't need to know it.
1163 See also "hash_seed()" and "hash_traversal_mask()".
1164 An example output might be:
1166 HASH_FUNCTION = ONE_AT_A_TIME_HARD HASH_SEED = 0x652e9b9349a7a032 PERTURB_KEYS = 1 (RANDOM)
1168 PERL_MEM_LOG
1170 If your Perl was configured with -Accflags=-DPERL_MEM_LOG,
1171 setting the environment variable "PERL_MEM_LOG" enables
1172 logging debug messages. The value has the form
1173 "<number>[m][s][t]", where "number" is the file descriptor
1174 number you want to write to (2 is default), and the
1175 combination of letters specifies that you want information
1176 about (m)emory and/or (s)v, optionally with (t)imestamps.
1177 For example, "PERL_MEM_LOG=1mst" logs all information to
1178 stdout. You can write to other opened file descriptors in a
1179 variety of ways:
1180 $ 3>foo3 PERL_MEM_LOG=3m perl ...
1182 PERL_ROOT (specific to the VMS port)
1184 A translation-concealed rooted logical name that contains
1185 Perl and the logical device for the @INC path on VMS only.
1186 Other logical names that affect Perl on VMS include
1187 PERLSHR, PERL_ENV_TABLES, and SYS$TIMEZONE_DIFFERENTIAL,
1188 but are optional and discussed further in perlvms and in
1189 README.vms in the Perl source distribution.
1190 PERL_SIGNALS
1192 Available in Perls 5.8.1 and later. If set to "unsafe",
1193 the pre-Perl-5.8.0 signal behaviour (which is immediate but
1194 unsafe) is restored. If set to "safe", then safe (but
1195 deferred) signals are used. See "Deferred Signals (Safe
1196 Signals)" in perlipc.
1197 PERL_UNICODE
1199 Equivalent to the -C command-line switch. Note that this
1200 is not a boolean variable. Setting this to "1" is not the
1201 right way to "enable Unicode" (whatever that would mean).
1202 You can use "0" to "disable Unicode", though (or
1203 alternatively unset PERL_UNICODE in your shell before
1204 starting Perl). See the description of the -C switch for
1205 more information.
1206 PERL_USE_UNSAFE_INC
1208 If perl has been configured to not have the current
1209 directory in @INC by default, this variable can be set to
1210 "1" to reinstate it. It's primarily intended for use while
1211 building and testing modules that have not been updated to
1212 deal with "." not being in @INC and should not be set in
1213 the environment for day-to-day use.
1214 SYS$LOGIN (specific to the VMS port)
1216 Used if chdir has no argument and "HOME" and "LOGDIR" are
1217 not set.
1218 PERL_INTERNAL_RAND_SEED
1220 Set to a non-negative integer to seed the random number
1221 generator used internally by perl for a variety of
1222 purposes.
1223 Ignored if perl is run setuid or setgid. Used only for
1225 some limited startup randomization (hash keys) if "-T" or
1226 "-t" perl is started with tainting enabled.
1227 Perl may be built to ignore this variable.
1229 Perl also has environment variables that control how Perl handles data
1231 specific to particular natural languages; see perllocale.
1232 Perl and its various modules and components, including its test
1234 frameworks, may sometimes make use of certain other environment
1235 variables. Some of these are specific to a particular platform.
1236 Please consult the appropriate module documentation and any
1237 documentation for your platform (like perlsolaris, perllinux,
1238 perlmacosx, perlwin32, etc) for variables peculiar to those specific
1239 situations.
1240 Perl makes all environment variables available to the program being
1242 executed, and passes these along to any child processes it starts.
1243 However, programs running setuid would do well to execute the following
1244 lines before doing anything else, just to keep people honest:
1245 $ENV{PATH} = "/bin:/usr/bin"; # or whatever you need
1247 $ENV{SHELL} = "/bin/sh" if exists $ENV{SHELL};
1248 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};
1249
1251 Some options, in particular "-I", "-M", "PERL5LIB" and "PERL5OPT" can
1252 interact, and the order in which they are applied is important.
1253 Note that this section does not document what actually happens inside
1255 the perl interpreter, it documents what effectively happens.
1256 -I The effect of multiple "-I" options is to "unshift" them onto @INC
1258 from right to left. So for example:
1259 perl -I 1 -I 2 -I 3
1261 will first prepend 3 onto the front of @INC, then prepend 2, and
1263 then prepend 1. The result is that @INC begins with:
1264 qw(1 2 3)
1266 -M Multiple "-M" options are processed from left to right. So this:
1268 perl -Mlib=1 -Mlib=2 -Mlib=3
1270 will first use the lib pragma to prepend 1 to @INC, then it will
1272 prepend 2, then it will prepend 3, resulting in an @INC that begins
1273 with:
1274 qw(3 2 1)
1276 the PERL5LIB environment variable
1278 This contains a list of directories, separated by colons. The
1279 entire list is prepended to @INC in one go. This:
1280 PERL5LIB=1:2:3 perl
1282 will result in an @INC that begins with:
1284 qw(1 2 3)
1286 combinations of -I, -M and PERL5LIB
1288 "PERL5LIB" is applied first, then all the "-I" arguments, then all
1289 the "-M" arguments. This:
1290 PERL5LIB=e1:e2 perl -I i1 -Mlib=m1 -I i2 -Mlib=m2
1292 will result in an @INC that begins with:
1294 qw(m2 m1 i1 i2 e1 e2)
1296 the PERL5OPT environment variable
1298 This contains a space separated list of switches. We only consider
1299 the effects of "-M" and "-I" in this section.
1300 After normal processing of "-I" switches from the command line, all
1302 the "-I" switches in "PERL5OPT" are extracted. They are processed
1303 from left to right instead of from right to left. Also note that
1304 while whitespace is allowed between a "-I" and its directory on the
1305 command line, it is not allowed in "PERL5OPT".
1306 After normal processing of "-M" switches from the command line, all
1308 the "-M" switches in "PERL5OPT" are extracted. They are processed
1309 from left to right, i.e. the same as those on the command line.
1310 An example may make this clearer:
1312 export PERL5OPT="-Mlib=optm1 -Iopti1 -Mlib=optm2 -Iopti2"
1314 export PERL5LIB=e1:e2
1315 perl -I i1 -Mlib=m1 -I i2 -Mlib=m2
1316 will result in an @INC that begins with:
1318 qw(
1320 optm2
1321 optm1
1322 m2
1324 m1
1325 opti2
1327 opti1
1328 i1
1330 i2
1331 e1
1333 e2
1334 )
1335 Other complications
1337 There are some complications that are ignored in the examples
1338 above:
1339 arch and version subdirs
1341 All of "-I", "PERL5LIB" and "use lib" will also prepend arch
1342 and version subdirs if they are present
1343 sitecustomize.pl
1345perl v5.34.0 2021-10-18 PERLRUN(1)