3 perlrun - how to execute the Perl interpreter
7 B<perl> S<[ B<-sTtuUWX> ]>
8 S<[ B<-hv> ] [ B<-V>[:I<configvar>] ]>
9 S<[ B<-cw> ] [ B<-d>[B<t>][:I<debugger>] ] [ B<-D>[I<number/list>] ]>
10 S<[ B<-pna> ] [ B<-F>I<pattern> ] [ B<-l>[I<octal>] ] [ B<-0>[I<octal/hexadecimal>] ]>
11 S<[ B<-I>I<dir> ] [ B<-m>[B<->]I<module> ] [ B<-M>[B<->]I<'module...'> ] [ B<-f> ]>
12 S<[ B<-C [I<number/list>] >]>
15 S<[ B<-i>[I<extension>] ]>
16 S<[ [B<-e>|B<-E>] I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...>
20 The normal way to run a Perl program is by making it directly
21 executable, or else by passing the name of the source file as an
22 argument on the command line. (An interactive Perl environment
23 is also possible--see L<perldebug> for details on how to do that.)
24 Upon startup, Perl looks for your program in one of the following
31 Specified line by line via B<-e> or B<-E> switches on the command line.
35 Contained in the file specified by the first filename on the command line.
36 (Note that systems supporting the C<#!> notation invoke interpreters this
37 way. See L<Location of Perl>.)
41 Passed in implicitly via standard input. This works only if there are
42 no filename arguments--to pass arguments to a STDIN-read program you
43 must explicitly specify a "-" for the program name.
47 With methods 2 and 3, Perl starts parsing the input file from the
48 beginning, unless you've specified a B<-x> switch, in which case it
49 scans for the first line starting with C<#!> and containing the word
50 "perl", and starts there instead. This is useful for running a program
51 embedded in a larger message. (In this case you would indicate the end
52 of the program using the C<__END__> token.)
54 The C<#!> line is always examined for switches as the line is being
55 parsed. Thus, if you're on a machine that allows only one argument
56 with the C<#!> line, or worse, doesn't even recognize the C<#!> line, you
57 still can get consistent switch behaviour regardless of how Perl was
58 invoked, even if B<-x> was used to find the beginning of the program.
60 Because historically some operating systems silently chopped off
61 kernel interpretation of the C<#!> line after 32 characters, some
62 switches may be passed in on the command line, and some may not;
63 you could even get a "-" without its letter, if you're not careful.
64 You probably want to make sure that all your switches fall either
65 before or after that 32-character boundary. Most switches don't
66 actually care if they're processed redundantly, but getting a "-"
67 instead of a complete switch could cause Perl to try to execute
68 standard input instead of your program. And a partial B<-I> switch
69 could also cause odd results.
71 Some switches do care if they are processed twice, for instance
72 combinations of B<-l> and B<-0>. Either put all the switches after
73 the 32-character boundary (if applicable), or replace the use of
74 B<-0>I<digits> by C<BEGIN{ $/ = "\0digits"; }>.
76 Parsing of the C<#!> switches starts wherever "perl" is mentioned in the line.
77 The sequences "-*" and "- " are specifically ignored so that you could,
78 if you were so inclined, say
82 eval 'exec perl -x -wS $0 ${1+"$@"}'
85 to let Perl see the B<-p> switch.
87 A similar trick involves the I<env> program, if you have it.
91 The examples above use a relative path to the perl interpreter,
92 getting whatever version is first in the user's path. If you want
93 a specific version of Perl, say, perl5.14.1, you should place
94 that directly in the C<#!> line's path.
96 If the C<#!> line does not contain the word "perl" nor the word "indir"
97 the program named after the C<#!> is executed instead of the Perl
98 interpreter. This is slightly bizarre, but it helps people on machines
99 that don't do C<#!>, because they can tell a program that their SHELL is
100 F</usr/bin/perl>, and Perl will then dispatch the program to the correct
101 interpreter for them.
103 After locating your program, Perl compiles the entire program to an
104 internal form. If there are any compilation errors, execution of the
105 program is not attempted. (This is unlike the typical shell script,
106 which might run part-way through before finding a syntax error.)
108 If the program is syntactically correct, it is executed. If the program
109 runs off the end without hitting an exit() or die() operator, an implicit
110 C<exit(0)> is provided to indicate successful completion.
112 =head2 #! and quoting on non-Unix systems
115 Unix's C<#!> technique can be simulated on other systems:
123 extproc perl -S -your_switches
125 as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's
130 Create a batch file to run your program, and codify it in
131 C<ALTERNATE_SHEBANG> (see the F<dosish.h> file in the source
132 distribution for more information).
136 The Win95/NT installation, when using the ActiveState installer for Perl,
137 will modify the Registry to associate the F<.pl> extension with the perl
138 interpreter. If you install Perl by other means (including building from
139 the sources), you may have to modify the Registry yourself. Note that
140 this means you can no longer tell the difference between an executable
141 Perl program and a Perl library file.
147 $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
148 $ exit++ + ++$status != 0 and $exit = $status = undef;
150 at the top of your program, where B<-mysw> are any command line switches you
151 want to pass to Perl. You can now invoke the program directly, by saying
152 C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly
153 via F<DCL$PATH> by just using the name of the program).
155 This incantation is a bit much to remember, but Perl will display it for
156 you if you say C<perl "-V:startperl">.
160 Command-interpreters on non-Unix systems have rather different ideas
161 on quoting than Unix shells. You'll need to learn the special
162 characters in your command-interpreter (C<*>, C<\> and C<"> are
163 common) and how to protect whitespace and these characters to run
164 one-liners (see L<-e|/-e commandline> below).
166 On some systems, you may have to change single-quotes to double ones,
167 which you must I<not> do on Unix or Plan 9 systems. You might also
168 have to change a single % to a %%.
173 perl -e 'print "Hello world\n"'
176 perl -e "print \"Hello world\n\""
179 perl -e "print ""Hello world\n"""
181 The problem is that none of this is reliable: it depends on the
182 command and it is entirely possible neither works. If I<4DOS> were
183 the command shell, this would probably work better:
185 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
187 B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in
188 when nobody was looking, but just try to find documentation for its
191 There is no general solution to all of this. It's just a mess.
193 =head2 Location of Perl
194 X<perl, location of interpreter>
196 It may seem obvious to say, but Perl is useful only when users can
197 easily find it. When possible, it's good for both F</usr/bin/perl>
198 and F</usr/local/bin/perl> to be symlinks to the actual binary. If
199 that can't be done, system administrators are strongly encouraged
200 to put (symlinks to) perl and its accompanying utilities into a
201 directory typically found along a user's PATH, or in some other
202 obvious and convenient place.
204 In this documentation, C<#!/usr/bin/perl> on the first line of the program
205 will stand in for whatever method works on your system. You are
206 advised to use a specific path if you care about a specific version.
208 #!/usr/local/bin/perl5.14
210 or if you just want to be running at least version, place a statement
211 like this at the top of your program:
215 =head2 Command Switches
216 X<perl, command switches> X<command switches>
218 As with all standard commands, a single-character switch may be
219 clustered with the following switch, if any.
221 #!/usr/bin/perl -spi.orig # same as -s -p -i.orig
227 =item B<-0>[I<octal/hexadecimal>]
230 specifies the input record separator (C<$/>) as an octal or
231 hexadecimal number. If there are no digits, the null character is the
232 separator. Other switches may precede or follow the digits. For
233 example, if you have a version of I<find> which can print filenames
234 terminated by the null character, you can say this:
236 find . -name '*.orig' -print0 | perl -n0e unlink
238 The special value 00 will cause Perl to slurp files in paragraph mode.
239 Any value 0400 or above will cause Perl to slurp files whole, but by convention
240 the value 0777 is the one normally used for this purpose.
242 You can also specify the separator character using hexadecimal notation:
243 B<-0xI<HHH...>>, where the C<I<H>> are valid hexadecimal digits. Unlike
244 the octal form, this one may be used to specify any Unicode character, even
245 those beyond 0xFF. So if you I<really> want a record separator of 0777,
246 specify it as B<-0x1FF>. (This means that you cannot use the B<-x> option
247 with a directory name that consists of hexadecimal digits, or else Perl
248 will think you have specified a hex number to B<-0>.)
253 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
254 split command to the @F array is done as the first thing inside the
255 implicit while loop produced by the B<-n> or B<-p>.
257 perl -ane 'print pop(@F), "\n";'
266 An alternate delimiter may be specified using B<-F>.
268 B<-a> implicitly sets B<-n>.
270 =item B<-C [I<number/list>]>
273 The B<-C> flag controls some of the Perl Unicode features.
275 As of 5.8.1, the B<-C> can be followed either by a number or a list
276 of option letters. The letters, their numeric values, and effects
277 are as follows; listing the letters is equal to summing the numbers.
279 I 1 STDIN is assumed to be in UTF-8
280 O 2 STDOUT will be in UTF-8
281 E 4 STDERR will be in UTF-8
283 i 8 UTF-8 is the default PerlIO layer for input streams
284 o 16 UTF-8 is the default PerlIO layer for output streams
286 A 32 the @ARGV elements are expected to be strings encoded
288 L 64 normally the "IOEioA" are unconditional, the L makes
289 them conditional on the locale environment variables
290 (the LC_ALL, LC_TYPE, and LANG, in the order of
291 decreasing precedence) -- if the variables indicate
292 UTF-8, then the selected "IOEioA" are in effect
293 a 256 Set ${^UTF8CACHE} to -1, to run the UTF-8 caching
294 code in debugging mode.
296 =for documenting_the_underdocumented
297 perl.h gives W/128 as PERL_UNICODE_WIDESYSCALLS "/* for Sarathy */"
300 perltodo mentions Unicode in %ENV and filenames. I guess that these will be
301 options e and f (or F).
303 For example, B<-COE> and B<-C6> will both turn on UTF-8-ness on both
304 STDOUT and STDERR. Repeating letters is just redundant, not cumulative
307 The C<io> options mean that any subsequent open() (or similar I/O
308 operations) in the current file scope will have the C<:utf8> PerlIO layer
309 implicitly applied to them, in other words, UTF-8 is expected from any
310 input stream, and UTF-8 is produced to any output stream. This is just
311 the default, with explicit layers in open() and with binmode() one can
312 manipulate streams as usual.
314 B<-C> on its own (not followed by any number or option list), or the
315 empty string C<""> for the C<PERL_UNICODE> environment variable, has the
316 same effect as B<-CSDL>. In other words, the standard I/O handles and
317 the default C<open()> layer are UTF-8-fied I<but> only if the locale
318 environment variables indicate a UTF-8 locale. This behaviour follows
319 the I<implicit> (and problematic) UTF-8 behaviour of Perl 5.8.0.
320 (See L<perl581delta/UTF-8 no longer default under UTF-8 locales>.)
322 You can use B<-C0> (or C<"0"> for C<PERL_UNICODE>) to explicitly
323 disable all the above Unicode features.
325 The read-only magic variable C<${^UNICODE}> reflects the numeric value
326 of this setting. This variable is set during Perl startup and is
327 thereafter read-only. If you want runtime effects, use the three-arg
328 open() (see L<perlfunc/open>), the two-arg binmode() (see L<perlfunc/binmode>),
329 and the C<open> pragma (see L<open>).
331 (In Perls earlier than 5.8.1 the B<-C> switch was a Win32-only switch
332 that enabled the use of Unicode-aware "wide system call" Win32 APIs.
333 This feature was practically unused, however, and the command line
334 switch was therefore "recycled".)
336 B<Note:> Since perl 5.10.1, if the B<-C> option is used on the C<#!> line,
337 it must be specified on the command line as well, since the standard streams
338 are already set up at this point in the execution of the perl interpreter.
339 You can also use binmode() to set the encoding of an I/O stream.
344 causes Perl to check the syntax of the program and then exit without
345 executing it. Actually, it I<will> execute and C<BEGIN>, C<UNITCHECK>,
346 or C<CHECK> blocks and any C<use> statements: these are considered as
347 occurring outside the execution of your program. C<INIT> and C<END>
348 blocks, however, will be skipped.
355 runs the program under the Perl debugger. See L<perldebug>.
356 If B<t> is specified, it indicates to the debugger that threads
357 will be used in the code being debugged.
359 =item B<-d:>I<MOD[=bar,baz]>
362 =item B<-dt:>I<MOD[=bar,baz]>
364 runs the program under the control of a debugging, profiling, or tracing
365 module installed as C<Devel::I<MOD>>. E.g., B<-d:DProf> executes the
366 program using the C<Devel::DProf> profiler. As with the B<-M> flag, options
367 may be passed to the C<Devel::I<MOD>> package where they will be received
368 and interpreted by the C<Devel::I<MOD>::import> routine. Again, like B<-M>,
369 use -B<-d:-I<MOD>> to call C<Devel::I<MOD>::unimport> instead of import. The
370 comma-separated list of options must follow a C<=> character. If B<t> is
371 specified, it indicates to the debugger that threads will be used in the
372 code being debugged. See L<perldebug>.
374 =item B<-D>I<letters>
375 X<-D> X<DEBUGGING> X<-DDEBUGGING>
379 sets debugging flags. To watch how it executes your program, use
380 B<-Dtls>. (This works only if debugging is compiled into your
381 Perl.) Another nice value is B<-Dx>, which lists your compiled
382 syntax tree. And B<-Dr> displays compiled regular expressions;
383 the format of the output is explained in L<perldebguts>.
385 As an alternative, specify a number instead of list of letters (e.g.,
386 B<-D14> is equivalent to B<-Dtls>):
388 1 p Tokenizing and parsing (with v, displays parse stack)
389 2 s Stack snapshots (with v, displays all stacks)
390 4 l Context (loop) stack processing
392 16 o Method and overloading resolution
393 32 c String/numeric conversions
394 64 P Print profiling info, source file input state
395 128 m Memory and SV allocation
396 256 f Format processing
397 512 r Regular expression parsing and execution
398 1024 x Syntax tree dump
399 2048 u Tainting checks
400 4096 U Unofficial, User hacking (reserved for private,
402 8192 H Hash dump -- usurps values()
403 16384 X Scratchpad allocation
405 65536 S Op slab allocation
407 262144 R Include reference counts of dumped variables (eg when
409 524288 J show s,t,P-debug (don't Jump over) on opcodes within
411 1048576 v Verbose: use in conjunction with other flags
412 2097152 C Copy On Write
413 4194304 A Consistency checks on internal structures
414 8388608 q quiet - currently only suppresses the "EXECUTING"
416 16777216 M trace smart match resolution
417 33554432 B dump suBroutine definitions, including special Blocks
420 All these flags require B<-DDEBUGGING> when you compile the Perl
421 executable (but see C<:opd> in L<Devel::Peek> or L<re/'debug' mode>
422 which may change this).
423 See the F<INSTALL> file in the Perl source distribution
424 for how to do this. This flag is automatically set if you include B<-g>
425 option when C<Configure> asks you about optimizer/debugger flags.
427 If you're just trying to get a print out of each line of Perl code
428 as it executes, the way that C<sh -x> provides for shell scripts,
429 you can't use Perl's B<-D> switch. Instead do this
431 # If you have "env" utility
432 env PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
434 # Bourne shell syntax
435 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
438 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
440 See L<perldebug> for details and variations.
442 =item B<-e> I<commandline>
445 may be used to enter one line of program. If B<-e> is given, Perl
446 will not look for a filename in the argument list. Multiple B<-e>
447 commands may be given to build up a multi-line script. Make sure
448 to use semicolons where you would in a normal program.
450 =item B<-E> I<commandline>
453 behaves just like B<-e>, except that it implicitly enables all
454 optional features (in the main compilation unit). See L<feature>.
457 X<-f> X<sitecustomize> X<sitecustomize.pl>
459 Disable executing F<$Config{sitelib}/sitecustomize.pl> at startup.
461 Perl can be built so that it by default will try to execute
462 F<$Config{sitelib}/sitecustomize.pl> at startup (in a BEGIN block).
463 This is a hook that allows the sysadmin to customize how Perl behaves.
464 It can for instance be used to add entries to the @INC array to make Perl
465 find modules in non-standard locations.
467 Perl actually inserts the following code:
470 do { local $!; -f "$Config{sitelib}/sitecustomize.pl"; }
471 && do "$Config{sitelib}/sitecustomize.pl";
474 Since it is an actual C<do> (not a C<require>), F<sitecustomize.pl>
475 doesn't need to return a true value. The code is run in package C<main>,
476 in its own lexical scope. However, if the script dies, C<$@> will not
479 The value of C<$Config{sitelib}> is also determined in C code and not
480 read from C<Config.pm>, which is not loaded.
482 The code is executed I<very> early. For example, any changes made to
483 C<@INC> will show up in the output of `perl -V`. Of course, C<END>
484 blocks will be likewise executed very late.
486 To determine at runtime if this capability has been compiled in your
487 perl, you can check the value of C<$Config{usesitecustomize}>.
489 =item B<-F>I<pattern>
492 specifies the pattern to split on for B<-a>. The pattern may be
493 surrounded by C<//>, C<"">, or C<''>, otherwise it will be put in single
494 quotes. You can't use literal whitespace in the pattern.
496 B<-F> implicitly sets both B<-a> and B<-n>.
501 prints a summary of the options.
503 =item B<-i>[I<extension>]
506 specifies that files processed by the C<E<lt>E<gt>> construct are to be
507 edited in-place. It does this by renaming the input file, opening the
508 output file by the original name, and selecting that output file as the
509 default for print() statements. The extension, if supplied, is used to
510 modify the name of the old file to make a backup copy, following these
513 If no extension is supplied, and your system supports it, the original
514 I<file> is kept open without a name while the output is redirected to
515 a new file with the original I<filename>. When perl exits, cleanly or not,
516 the original I<file> is unlinked.
518 If the extension doesn't contain a C<*>, then it is appended to the
519 end of the current filename as a suffix. If the extension does
520 contain one or more C<*> characters, then each C<*> is replaced
521 with the current filename. In Perl terms, you could think of this
524 ($backup = $extension) =~ s/\*/$file_name/g;
526 This allows you to add a prefix to the backup file, instead of (or in
527 addition to) a suffix:
529 $ perl -pi'orig_*' -e 's/bar/baz/' fileA # backup to
532 Or even to place backup copies of the original files into another
533 directory (provided the directory already exists):
535 $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to
538 These sets of one-liners are equivalent:
540 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
541 $ perl -pi'*' -e 's/bar/baz/' fileA # overwrite current file
543 $ perl -pi'.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
544 $ perl -pi'*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
546 From the shell, saying
548 $ perl -p -i.orig -e "s/foo/bar/; ... "
550 is the same as using the program:
552 #!/usr/bin/perl -pi.orig
555 which is equivalent to
558 $extension = '.orig';
560 if ($ARGV ne $oldargv) {
561 if ($extension !~ /\*/) {
562 $backup = $ARGV . $extension;
565 ($backup = $extension) =~ s/\*/$ARGV/g;
567 rename($ARGV, $backup);
568 open(ARGVOUT, ">$ARGV");
575 print; # this prints to original filename
579 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
580 know when the filename has changed. It does, however, use ARGVOUT for
581 the selected filehandle. Note that STDOUT is restored as the default
582 output filehandle after the loop.
584 As shown above, Perl creates the backup file whether or not any output
585 is actually changed. So this is just a fancy way to copy files:
587 $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
589 $ perl -p -i'.orig' -e 1 file1 file2 file3...
591 You can use C<eof> without parentheses to locate the end of each input
592 file, in case you want to append to each file, or reset line numbering
593 (see example in L<perlfunc/eof>).
595 If, for a given file, Perl is unable to create the backup file as
596 specified in the extension then it will skip that file and continue on
597 with the next one (if it exists).
599 For a discussion of issues surrounding file permissions and B<-i>, see
600 L<perlfaq5/Why does Perl let me delete read-only files? Why does -i clobber
601 protected files? Isn't this a bug in Perl?>.
603 You cannot use B<-i> to create directories or to strip extensions from
606 Perl does not expand C<~> in filenames, which is good, since some
607 folks use it for their backup files:
609 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
611 Note that because B<-i> renames or deletes the original file before
612 creating a new file of the same name, Unix-style soft and hard links will
615 Finally, the B<-i> switch does not impede execution when no
616 files are given on the command line. In this case, no backup is made
617 (the original file cannot, of course, be determined) and processing
618 proceeds from STDIN to STDOUT as might be expected.
620 =item B<-I>I<directory>
623 Directories specified by B<-I> are prepended to the search path for
626 =item B<-l>[I<octnum>]
629 enables automatic line-ending processing. It has two separate
630 effects. First, it automatically chomps C<$/> (the input record
631 separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
632 (the output record separator) to have the value of I<octnum> so
633 that any print statements will have that separator added back on.
634 If I<octnum> is omitted, sets C<$\> to the current value of
635 C<$/>. For instance, to trim lines to 80 columns:
637 perl -lpe 'substr($_, 80) = ""'
639 Note that the assignment C<$\ = $/> is done when the switch is processed,
640 so the input record separator can be different than the output record
641 separator if the B<-l> switch is followed by a B<-0> switch:
643 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
645 This sets C<$\> to newline and then sets C<$/> to the null character.
647 =item B<-m>[B<->]I<module>
650 =item B<-M>[B<->]I<module>
652 =item B<-M>[B<->]I<'module ...'>
654 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
656 B<-m>I<module> executes C<use> I<module> C<();> before executing your
659 B<-M>I<module> executes C<use> I<module> C<;> before executing your
660 program. You can use quotes to add extra code after the module name,
661 e.g., C<'-MI<MODULE> qw(foo bar)'>.
663 If the first character after the B<-M> or B<-m> is a dash (B<->)
664 then the 'use' is replaced with 'no'.
666 A little builtin syntactic sugar means you can also say
667 B<-mI<MODULE>=foo,bar> or B<-MI<MODULE>=foo,bar> as a shortcut for
668 B<'-MI<MODULE> qw(foo bar)'>. This avoids the need to use quotes when
669 importing symbols. The actual code generated by B<-MI<MODULE>=foo,bar> is
670 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
671 removes the distinction between B<-m> and B<-M>.
673 A consequence of this is that B<-MI<MODULE>=number> never does a version check,
674 unless C<I<MODULE>::import()> itself is set up to do a version check, which
675 could happen for example if I<MODULE> inherits from L<Exporter>.
680 causes Perl to assume the following loop around your program, which
681 makes it iterate over filename arguments somewhat like I<sed -n> or
686 ... # your program goes here
689 Note that the lines are not printed by default. See L</-p> to have
690 lines printed. If a file named by an argument cannot be opened for
691 some reason, Perl warns you about it and moves on to the next file.
693 Also note that C<< <> >> passes command line arguments to
694 L<perlfunc/open>, which doesn't necessarily interpret them as file names.
695 See L<perlop> for possible security implications.
697 Here is an efficient way to delete all files that haven't been modified for
700 find . -mtime +7 -print | perl -nle unlink
702 This is faster than using the B<-exec> switch of I<find> because you don't
703 have to start a process on every filename found. It does suffer from
704 the bug of mishandling newlines in pathnames, which you can fix if
705 you follow the example under B<-0>.
707 C<BEGIN> and C<END> blocks may be used to capture control before or after
708 the implicit program loop, just as in I<awk>.
713 causes Perl to assume the following loop around your program, which
714 makes it iterate over filename arguments somewhat like I<sed>:
719 ... # your program goes here
721 print or die "-p destination: $!\n";
724 If a file named by an argument cannot be opened for some reason, Perl
725 warns you about it, and moves on to the next file. Note that the
726 lines are printed automatically. An error occurring during printing is
727 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
728 overrides a B<-n> switch.
730 C<BEGIN> and C<END> blocks may be used to capture control before or after
731 the implicit loop, just as in I<awk>.
736 enables rudimentary switch parsing for switches on the command
737 line after the program name but before any filename arguments (or before
738 an argument of B<-->). Any switch found there is removed from @ARGV and sets the
739 corresponding variable in the Perl program. The following program
740 prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
741 if it is invoked with B<-xyz=abc>.
744 if ($xyz) { print "$xyz\n" }
746 Do note that a switch like B<--help> creates the variable C<${-help}>, which is
747 not compliant with C<use strict "refs">. Also, when using this option on a
748 script with warnings enabled you may get a lot of spurious "used only once"
754 makes Perl use the PATH environment variable to search for the
755 program unless the name of the program contains path separators.
757 On some platforms, this also makes Perl append suffixes to the
758 filename while searching for it. For example, on Win32 platforms,
759 the ".bat" and ".cmd" suffixes are appended if a lookup for the
760 original name fails, and if the name does not already end in one
761 of those suffixes. If your Perl was compiled with C<DEBUGGING> turned
762 on, using the B<-Dp> switch to Perl shows how the search progresses.
764 Typically this is used to emulate C<#!> startup on platforms that don't
765 support C<#!>. It's also convenient when debugging a script that uses C<#!>,
766 and is thus normally found by the shell's $PATH search mechanism.
768 This example works on many platforms that have a shell compatible with
772 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
773 if $running_under_some_shell;
775 The system ignores the first line and feeds the program to F</bin/sh>,
776 which proceeds to try to execute the Perl program as a shell script.
777 The shell executes the second line as a normal shell command, and thus
778 starts up the Perl interpreter. On some systems $0 doesn't always
779 contain the full pathname, so the B<-S> tells Perl to search for the
780 program if necessary. After Perl locates the program, it parses the
781 lines and ignores them because the variable $running_under_some_shell
782 is never true. If the program will be interpreted by csh, you will need
783 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
784 embedded spaces (and such) in the argument list. To start up I<sh> rather
785 than I<csh>, some systems may have to replace the C<#!> line with a line
786 containing just a colon, which will be politely ignored by Perl. Other
787 systems can't control that, and need a totally devious construct that
788 will work under any of I<csh>, I<sh>, or Perl, such as the following:
790 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
791 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
792 if $running_under_some_shell;
794 If the filename supplied contains directory separators (and so is an
795 absolute or relative pathname), and if that file is not found,
796 platforms that append file extensions will do so and try to look
797 for the file with those extensions added, one by one.
799 On DOS-like platforms, if the program does not contain directory
800 separators, it will first be searched for in the current directory
801 before being searched for on the PATH. On Unix platforms, the
802 program will be searched for strictly on the PATH.
807 Like B<-T>, but taint checks will issue warnings rather than fatal
808 errors. These warnings can now be controlled normally with C<no warnings
811 B<Note: This is not a substitute for C<-T>!> This is meant to be
812 used I<only> as a temporary development aid while securing legacy code:
813 for real production code and for new secure code written from scratch,
814 always use the real B<-T>.
819 turns on "taint" so you can test them. Ordinarily
820 these checks are done only when running setuid or setgid. It's a
821 good idea to turn them on explicitly for programs that run on behalf
822 of someone else whom you might not necessarily trust, such as CGI
823 programs or any internet servers you might write in Perl. See
824 L<perlsec> for details. For security reasons, this option must be
825 seen by Perl quite early; usually this means it must appear early
826 on the command line or in the C<#!> line for systems which support
832 This switch causes Perl to dump core after compiling your
833 program. You can then in theory take this core dump and turn it
834 into an executable file by using the I<undump> program (not supplied).
835 This speeds startup at the expense of some disk space (which you
836 can minimize by stripping the executable). (Still, a "hello world"
837 executable comes out to about 200K on my machine.) If you want to
838 execute a portion of your program before dumping, use the dump()
839 operator instead. Note: availability of I<undump> is platform
840 specific and may not be available for a specific port of Perl.
845 allows Perl to do unsafe operations. Currently the only "unsafe"
846 operations are attempting to unlink directories while running as superuser
847 and running setuid programs with fatal taint checks turned into warnings.
848 Note that warnings must be enabled along with this option to actually
849 I<generate> the taint-check warnings.
854 prints the version and patchlevel of your perl executable.
859 prints summary of the major perl configuration values and the current
862 =item B<-V:>I<configvar>
864 Prints to STDOUT the value of the named configuration variable(s),
865 with multiples when your C<I<configvar>> argument looks like a regex (has
866 non-letters). For example:
869 libc='/lib/libc-2.2.4.so';
871 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
872 libc='/lib/libc-2.2.4.so';
874 libpth='/usr/local/lib /lib /usr/lib';
875 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
877 libc='/lib/libc-2.2.4.so';
881 Additionally, extra colons can be used to control formatting. A
882 trailing colon suppresses the linefeed and terminator ";", allowing
883 you to embed queries into shell commands. (mnemonic: PATH separator
886 $ echo "compression-vars: " `perl -V:z.*: ` " are here !"
887 compression-vars: zcat='' zip='zip' are here !
889 A leading colon removes the "name=" part of the response, this allows
890 you to map to the name you need. (mnemonic: empty label)
892 $ echo "goodvfork="`./perl -Ilib -V::usevfork`
895 Leading and trailing colons can be used together if you need
896 positional parameter values without the names. Note that in the case
897 below, the C<PERL_API> params are returned in alphabetical order.
899 $ echo building_on `perl -V::osname: -V::PERL_API_.*:` now
900 building_on 'linux' '5' '1' '9' now
905 prints warnings about dubious constructs, such as variable names
906 mentioned only once and scalar variables used
907 before being set; redefined subroutines; references to undefined
908 filehandles; filehandles opened read-only that you are attempting
909 to write on; values used as a number that don't I<look> like numbers;
910 using an array as though it were a scalar; if your subroutines
911 recurse more than 100 deep; and innumerable other things.
913 This switch really just enables the global C<$^W> variable; normally,
914 the lexically scoped C<use warnings> pragma is preferred. You
915 can disable or promote into fatal errors specific warnings using
916 C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
917 See also L<perldiag> and L<perltrap>. A fine-grained warning
918 facility is also available if you want to manipulate entire classes
919 of warnings; see L<warnings> or L<perllexwarn>.
924 Enables all warnings regardless of C<no warnings> or C<$^W>.
930 Disables all warnings regardless of C<use warnings> or C<$^W>.
936 =item B<-x>I<directory>
938 tells Perl that the program is embedded in a larger chunk of unrelated
939 text, such as in a mail message. Leading garbage will be
940 discarded until the first line that starts with C<#!> and contains the
941 string "perl". Any meaningful switches on that line will be applied.
943 All references to line numbers by the program (warnings, errors, ...)
944 will treat the C<#!> line as the first line.
945 Thus a warning on the 2nd line of the program, which is on the 100th
946 line in the file will be reported as line 2, not as line 100.
947 This can be overridden by using the C<#line> directive.
948 (See L<perlsyn/"Plain Old Comments (Not!)">)
950 If a directory name is specified, Perl will switch to that directory
951 before running the program. The B<-x> switch controls only the
952 disposal of leading garbage. The program must be terminated with
953 C<__END__> if there is trailing garbage to be ignored; the program
954 can process any or all of the trailing garbage via the C<DATA> filehandle
957 The directory, if specified, must appear immediately following the B<-x>
958 with no intervening whitespace.
963 X<perl, environment variables>
970 Used if C<chdir> has no argument.
975 Used if C<chdir> has no argument and HOME is not set.
980 Used in executing subprocesses, and in finding the program if B<-S> is
986 A list of directories in which to look for Perl library
987 files before looking in the standard library and the current
988 directory. Any architecture-specific and version-specific directories,
989 such as F<version/archname/>, F<version/>, or F<archname/> under the
990 specified locations are automatically included if they exist, with this
991 lookup done at interpreter startup time. In addition, any directories
992 matching the entries in C<$Config{inc_version_list}> are added.
993 (These typically would be for older compatible perl versions installed
994 in the same directory tree.)
996 If PERL5LIB is not defined, PERLLIB is used. Directories are separated
997 (like in PATH) by a colon on Unixish platforms and by a semicolon on
998 Windows (the proper path separator being given by the command C<perl
1001 When running taint checks, either because the program was running setuid or
1002 setgid, or the B<-T> or B<-t> switch was specified, neither PERL5LIB nor
1003 PERLLIB is consulted. The program should instead say:
1005 use lib "/my/directory";
1010 Command-line options (switches). Switches in this variable are treated
1011 as if they were on every Perl command line. Only the B<-[CDIMUdmtwW]>
1012 switches are allowed. When running taint checks (either because the
1013 program was running setuid or setgid, or because the B<-T> or B<-t>
1014 switch was used), this variable is ignored. If PERL5OPT begins with
1015 B<-T>, tainting will be enabled and subsequent options ignored. If
1016 PERL5OPT begins with B<-t>, tainting will be enabled, a writable dot
1017 removed from @INC, and subsequent options honored.
1022 A space (or colon) separated list of PerlIO layers. If perl is built
1023 to use PerlIO system for IO (the default) these layers affect Perl's IO.
1025 It is conventional to start layer names with a colon (for example, C<:perlio>) to
1026 emphasize their similarity to variable "attributes". But the code that parses
1027 layer specification strings, which is also used to decode the PERLIO
1028 environment variable, treats the colon as a separator.
1030 An unset or empty PERLIO is equivalent to the default set of layers for
1031 your platform; for example, C<:unix:perlio> on Unix-like systems
1032 and C<:unix:crlf> on Windows and other DOS-like systems.
1034 The list becomes the default for I<all> Perl's IO. Consequently only built-in
1035 layers can appear in this list, as external layers (such as C<:encoding()>) need
1036 IO in order to load them! See L<"open pragma"|open> for how to add external
1037 encodings as defaults.
1039 Layers it makes sense to include in the PERLIO environment
1040 variable are briefly summarized below. For more details see L<PerlIO>.
1047 A pseudolayer that turns the C<:utf8> flag I<off> for the layer below;
1048 unlikely to be useful on its own in the global PERLIO environment variable.
1049 You perhaps were thinking of C<:crlf:bytes> or C<:perlio:bytes>.
1054 A layer which does CRLF to C<"\n"> translation distinguishing "text" and
1055 "binary" files in the manner of MS-DOS and similar operating systems.
1056 (It currently does I<not> mimic MS-DOS as far as treating of Control-Z
1057 as being an end-of-file marker.)
1062 A layer that implements "reading" of files by using I<mmap>(2) to
1063 make an entire file appear in the process's address space, and then
1064 using that as PerlIO's "buffer".
1069 This is a re-implementation of stdio-like buffering written as a
1070 PerlIO layer. As such it will call whatever layer is below it for
1071 its operations, typically C<:unix>.
1076 An experimental pseudolayer that removes the topmost layer.
1077 Use with the same care as is reserved for nitroglycerine.
1082 A pseudolayer that manipulates other layers. Applying the C<:raw>
1083 layer is equivalent to calling C<binmode($fh)>. It makes the stream
1084 pass each byte as-is without translation. In particular, both CRLF
1085 translation and intuiting C<:utf8> from the locale are disabled.
1087 Unlike in earlier versions of Perl, C<:raw> is I<not>
1088 just the inverse of C<:crlf>: other layers which would affect the
1089 binary nature of the stream are also removed or disabled.
1094 This layer provides a PerlIO interface by wrapping system's ANSI C "stdio"
1095 library calls. The layer provides both buffering and IO.
1096 Note that the C<:stdio> layer does I<not> do CRLF translation even if that
1097 is the platform's normal behaviour. You will need a C<:crlf> layer above it
1103 Low-level layer that calls C<read>, C<write>, C<lseek>, etc.
1108 A pseudolayer that enables a flag in the layer below to tell Perl
1109 that output should be in utf8 and that input should be regarded as
1110 already in valid utf8 form. B<WARNING: It does not check for validity and as such
1111 should be handled with extreme caution for input, because security violations
1112 can occur with non-shortest UTF-8 encodings, etc.> Generally C<:encoding(utf8)> is
1113 the best option when reading UTF-8 encoded data.
1118 On Win32 platforms this I<experimental> layer uses native "handle" IO
1119 rather than a Unix-like numeric file descriptor layer. Known to be
1120 buggy in this release (5.14).
1124 The default set of layers should give acceptable results on all platforms
1126 For Unix platforms that will be the equivalent of "unix perlio" or "stdio".
1127 Configure is set up to prefer the "stdio" implementation if the system's library
1128 provides for fast access to the buffer; otherwise, it uses the "unix perlio"
1131 On Win32 the default in this release (5.14) is "unix crlf". Win32's "stdio"
1132 has a number of bugs/mis-features for Perl IO which are somewhat depending
1133 on the version and vendor of the C compiler. Using our own C<crlf> layer as
1134 the buffer avoids those issues and makes things more uniform. The C<crlf>
1135 layer provides CRLF conversion as well as buffering.
1137 This release (5.14) uses C<unix> as the bottom layer on Win32, and so still
1138 uses the C compiler's numeric file descriptor routines. There is an
1139 experimental native C<win32> layer, which is expected to be enhanced and
1140 should eventually become the default under Win32.
1142 The PERLIO environment variable is completely ignored when Perl
1143 is run in taint mode.
1148 If set to the name of a file or device, certain operations of PerlIO
1149 subsystem will be logged to that file, which is opened in append mode.
1150 Typical uses are in Unix:
1152 % env PERLIO_DEBUG=/dev/tty perl script ...
1154 and under Win32, the approximately equivalent:
1156 > set PERLIO_DEBUG=CON
1159 This functionality is disabled for setuid scripts and for scripts run
1165 A list of directories in which to look for Perl library
1166 files before looking in the standard library and the current directory.
1167 If PERL5LIB is defined, PERLLIB is not used.
1169 The PERLLIB environment variable is completely ignored when Perl
1170 is run in taint mode.
1175 The command used to load the debugger code. The default is:
1177 BEGIN { require "perl5db.pl" }
1179 The PERL5DB environment variable is only used when Perl is started with
1180 a bare B<-d> switch.
1182 =item PERL5DB_THREADED
1185 If set to a true value, indicates to the debugger that the code being
1186 debugged uses threads.
1188 =item PERL5SHELL (specific to the Win32 port)
1191 On Win32 ports only, may be set to an alternative shell that Perl must use
1192 internally for executing "backtick" commands or system(). Default is
1193 C<cmd.exe /x/d/c> on WindowsNT and C<command.com /c> on Windows95. The
1194 value is considered space-separated. Precede any character that
1195 needs to be protected, like a space or backslash, with another backslash.
1197 Note that Perl doesn't use COMSPEC for this purpose because
1198 COMSPEC has a high degree of variability among users, leading to
1199 portability concerns. Besides, Perl can use a shell that may not be
1200 fit for interactive use, and setting COMSPEC to such a shell may
1201 interfere with the proper functioning of other programs (which usually
1202 look in COMSPEC to find a shell fit for interactive use).
1204 Before Perl 5.10.0 and 5.8.8, PERL5SHELL was not taint checked
1205 when running external commands. It is recommended that
1206 you explicitly set (or delete) C<$ENV{PERL5SHELL}> when running
1207 in taint mode under Windows.
1209 =item PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
1210 X<PERL_ALLOW_NON_IFS_LSP>
1212 Set to 1 to allow the use of non-IFS compatible LSPs (Layered Service Providers).
1213 Perl normally searches for an IFS-compatible LSP because this is required
1214 for its emulation of Windows sockets as real filehandles. However, this may
1215 cause problems if you have a firewall such as I<McAfee Guardian>, which requires
1216 that all applications use its LSP but which is not IFS-compatible, because clearly
1217 Perl will normally avoid using such an LSP.
1219 Setting this environment variable to 1 means that Perl will simply use the
1220 first suitable LSP enumerated in the catalog, which keeps I<McAfee Guardian>
1221 happy--and in that particular case Perl still works too because I<McAfee
1222 Guardian>'s LSP actually plays other games which allow applications
1223 requiring IFS compatibility to work.
1225 =item PERL_DEBUG_MSTATS
1226 X<PERL_DEBUG_MSTATS>
1228 Relevant only if Perl is compiled with the C<malloc> included with the Perl
1229 distribution; that is, if C<perl -V:d_mymalloc> is "define".
1231 If set, this dumps out memory statistics after execution. If set
1232 to an integer greater than one, also dumps out memory statistics
1235 =item PERL_DESTRUCT_LEVEL
1236 X<PERL_DESTRUCT_LEVEL>
1238 Relevant only if your Perl executable was built with B<-DDEBUGGING>,
1239 this controls the behaviour of global destruction of objects and other
1240 references. See L<perlhacktips/PERL_DESTRUCT_LEVEL> for more information.
1242 =item PERL_DL_NONLAZY
1245 Set to C<"1"> to have Perl resolve I<all> undefined symbols when it loads
1246 a dynamic library. The default behaviour is to resolve symbols when
1247 they are used. Setting this variable is useful during testing of
1248 extensions, as it ensures that you get an error on misspelled function
1249 names even if the test suite doesn't call them.
1254 If using the C<use encoding> pragma without an explicit encoding name, the
1255 PERL_ENCODING environment variable is consulted for an encoding name.
1257 =item PERL_HASH_SEED
1260 (Since Perl 5.8.1, new semantics in Perl 5.18.0) Used to override
1261 the randomization of Perl's internal hash function. The value is expressed
1262 in hexadecimal, and may include a leading 0x. Truncated patterns
1263 are treated as though they are suffixed with sufficient 0's as required.
1265 If the option is provided, and C<PERL_PERTURB_KEYS> is NOT set, then
1266 a value of '0' implies C<PERL_PERTURB_KEYS=0> and any other value
1267 implies C<PERL_PERTURB_KEYS=2>.
1269 B<PLEASE NOTE: The hash seed is sensitive information>. Hashes are
1270 randomized to protect against local and remote attacks against Perl
1271 code. By manually setting a seed, this protection may be partially or
1274 See L<perlsec/"Algorithmic Complexity Attacks"> and L</PERL_PERTURB_KEYS>
1275 L</PERL_HASH_SEED_DEBUG> for more information.
1277 =item PERL_PERTURB_KEYS
1278 X<PERL_PERTURB_KEYS>
1280 (Since Perl 5.18.0) Set to C<"0"> or C<"NO"> then traversing keys
1281 will be repeatable from run to run for the same PERL_HASH_SEED.
1282 Insertion into a hash will not change the order, except to provide
1283 for more space in the hash. When combined with setting PERL_HASH_SEED
1284 this mode is as close to pre 5.18 behavior as you can get.
1286 When set to C<"1"> or C<"RANDOM"> then traversing keys will be randomized.
1287 Every time a hash is inserted into the key order will change in a random
1288 fashion. The order may not be repeatable in a following program run
1289 even if the PERL_HASH_SEED has been specified. This is the default
1292 When set to C<"2"> or C<"DETERMINISTIC"> then inserting keys into a hash
1293 will cause the key order to change, but in a way that is repeatable
1294 from program run to program run.
1296 B<NOTE:> Use of this option is considered insecure, and is intended only
1297 for debugging non-deterministic behavior in Perl's hash function. Do
1298 not use it in production.
1300 See L<perlsec/"Algorithmic Complexity Attacks"> and L</PERL_HASH_SEED>
1301 and L</PERL_HASH_SEED_DEBUG> for more information. You can get and set the
1302 key traversal mask for a specific hash by using the C<hash_traversal_mask()>
1303 function from L<Hash::Util>.
1305 =item PERL_HASH_SEED_DEBUG
1306 X<PERL_HASH_SEED_DEBUG>
1308 (Since Perl 5.8.1.) Set to C<"1"> to display (to STDERR) information
1309 about the hash function, seed, and what type of key traversal
1310 randomization is in effect at the beginning of execution. This, combined
1311 with L</PERL_HASH_SEED> and L</PERL_PERTURB_KEYS> is intended to aid in
1312 debugging nondeterministic behaviour caused by hash randomization.
1314 B<Note> that any information about the hash function, especially the hash
1315 seed is B<sensitive information>: by knowing it, one can craft a denial-of-service
1316 attack against Perl code, even remotely; see L<perlsec/"Algorithmic Complexity Attacks">
1317 for more information. B<Do not disclose the hash seed> to people who
1318 don't need to know it. See also C<hash_seed()> and
1319 C<key_traversal_mask()> in L<Hash::Util>.
1321 An example output might be:
1323 HASH_FUNCTION = ONE_AT_A_TIME_HARD HASH_SEED = 0x652e9b9349a7a032 PERTURB_KEYS = 1 (RANDOM)
1328 If your Perl was configured with B<-Accflags=-DPERL_MEM_LOG>, setting
1329 the environment variable C<PERL_MEM_LOG> enables logging debug
1330 messages. The value has the form C<< <I<number>>[m][s][t] >>, where
1331 C<I<number>> is the file descriptor number you want to write to (2 is
1332 default), and the combination of letters specifies that you want
1333 information about (m)emory and/or (s)v, optionally with
1334 (t)imestamps. For example, C<PERL_MEM_LOG=1mst> logs all
1335 information to stdout. You can write to other opened file descriptors
1336 in a variety of ways:
1338 $ 3>foo3 PERL_MEM_LOG=3m perl ...
1340 =item PERL_ROOT (specific to the VMS port)
1343 A translation-concealed rooted logical name that contains Perl and the
1344 logical device for the @INC path on VMS only. Other logical names that
1345 affect Perl on VMS include PERLSHR, PERL_ENV_TABLES, and
1346 SYS$TIMEZONE_DIFFERENTIAL, but are optional and discussed further in
1347 L<perlvms> and in F<README.vms> in the Perl source distribution.
1352 Available in Perls 5.8.1 and later. If set to C<"unsafe">, the pre-Perl-5.8.0
1353 signal behaviour (which is immediate but unsafe) is restored. If set
1354 to C<safe>, then safe (but deferred) signals are used. See
1355 L<perlipc/"Deferred Signals (Safe Signals)">.
1360 Equivalent to the B<-C> command-line switch. Note that this is not
1361 a boolean variable. Setting this to C<"1"> is not the right way to
1362 "enable Unicode" (whatever that would mean). You can use C<"0"> to
1363 "disable Unicode", though (or alternatively unset PERL_UNICODE in
1364 your shell before starting Perl). See the description of the B<-C>
1365 switch for more information.
1367 =item SYS$LOGIN (specific to the VMS port)
1370 Used if chdir has no argument and HOME and LOGDIR are not set.
1374 Perl also has environment variables that control how Perl handles data
1375 specific to particular natural languages; see L<perllocale>.
1377 Perl and its various modules and components, including its test frameworks,
1378 may sometimes make use of certain other environment variables. Some of
1379 these are specific to a particular platform. Please consult the
1380 appropriate module documentation and any documentation for your platform
1381 (like L<perlsolaris>, L<perllinux>, L<perlmacosx>, L<perlwin32>, etc) for
1382 variables peculiar to those specific situations.
1384 Perl makes all environment variables available to the program being
1385 executed, and passes these along to any child processes it starts.
1386 However, programs running setuid would do well to execute the following
1387 lines before doing anything else, just to keep people honest:
1389 $ENV{PATH} = "/bin:/usr/bin"; # or whatever you need
1390 $ENV{SHELL} = "/bin/sh" if exists $ENV{SHELL};
1391 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};