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...'> ]>
15 S<[ B<-i>[I<extension>] ]>
16 S<[ B<-e> I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...>
17 S<[ B<-A [I<assertions>] >]>
18 S<[ B<-C [I<number/list>] >]>
22 The normal way to run a Perl program is by making it directly
23 executable, or else by passing the name of the source file as an
24 argument on the command line. (An interactive Perl environment
25 is also possible--see L<perldebug> for details on how to do that.)
26 Upon startup, Perl looks for your program in one of the following
33 Specified line by line via B<-e> switches on the command line.
37 Contained in the file specified by the first filename on the command line.
38 (Note that systems supporting the #! notation invoke interpreters this
39 way. See L<Location of Perl>.)
43 Passed in implicitly via standard input. This works only if there are
44 no filename arguments--to pass arguments to a STDIN-read program you
45 must explicitly specify a "-" for the program name.
49 With methods 2 and 3, Perl starts parsing the input file from the
50 beginning, unless you've specified a B<-x> switch, in which case it
51 scans for the first line starting with #! and containing the word
52 "perl", and starts there instead. This is useful for running a program
53 embedded in a larger message. (In this case you would indicate the end
54 of the program using the C<__END__> token.)
56 The #! line is always examined for switches as the line is being
57 parsed. Thus, if you're on a machine that allows only one argument
58 with the #! line, or worse, doesn't even recognize the #! line, you
59 still can get consistent switch behavior regardless of how Perl was
60 invoked, even if B<-x> was used to find the beginning of the program.
62 Because historically some operating systems silently chopped off
63 kernel interpretation of the #! line after 32 characters, some
64 switches may be passed in on the command line, and some may not;
65 you could even get a "-" without its letter, if you're not careful.
66 You probably want to make sure that all your switches fall either
67 before or after that 32-character boundary. Most switches don't
68 actually care if they're processed redundantly, but getting a "-"
69 instead of a complete switch could cause Perl to try to execute
70 standard input instead of your program. And a partial B<-I> switch
71 could also cause odd results.
73 Some switches do care if they are processed twice, for instance
74 combinations of B<-l> and B<-0>. Either put all the switches after
75 the 32-character boundary (if applicable), or replace the use of
76 B<-0>I<digits> by C<BEGIN{ $/ = "\0digits"; }>.
78 Parsing of the #! switches starts wherever "perl" is mentioned in the line.
79 The sequences "-*" and "- " are specifically ignored so that you could,
80 if you were so inclined, say
82 #!/bin/sh -- # -*- perl -*- -p
83 eval 'exec perl -wS $0 ${1+"$@"}'
84 if $running_under_some_shell;
86 to let Perl see the B<-p> switch.
88 A similar trick involves the B<env> program, if you have it.
92 The examples above use a relative path to the perl interpreter,
93 getting whatever version is first in the user's path. If you want
94 a specific version of Perl, say, perl5.005_57, you should place
95 that directly in the #! line's path.
97 If the #! line does not contain the word "perl", the program named after
98 the #! is executed instead of the Perl interpreter. This is slightly
99 bizarre, but it helps people on machines that don't do #!, because they
100 can tell a program that their SHELL is F</usr/bin/perl>, and Perl will then
101 dispatch the program to the correct 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
114 Unix's #! technique can be simulated on other systems:
122 extproc perl -S -your_switches
124 as the first line in C<*.cmd> file (B<-S> due to a bug in cmd.exe's
129 Create a batch file to run your program, and codify it in
130 C<ALTERNATE_SHEBANG> (see the F<dosish.h> file in the source
131 distribution for more information).
135 The Win95/NT installation, when using the ActiveState installer for Perl,
136 will modify the Registry to associate the F<.pl> extension with the perl
137 interpreter. If you install Perl by other means (including building from
138 the sources), you may have to modify the Registry yourself. Note that
139 this means you can no longer tell the difference between an executable
140 Perl program and a Perl library file.
144 Under "Classic" MacOS, a perl program will have the appropriate Creator and
145 Type, so that double-clicking them will invoke the MacPerl application.
146 Under Mac OS X, clickable apps can be made from any C<#!> script using Wil
147 Sanchez' DropScript utility: http://www.wsanchez.net/software/ .
153 $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
154 $ exit++ + ++$status != 0 and $exit = $status = undef;
156 at the top of your program, where B<-mysw> are any command line switches you
157 want to pass to Perl. You can now invoke the program directly, by saying
158 C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly
159 via F<DCL$PATH> by just using the name of the program).
161 This incantation is a bit much to remember, but Perl will display it for
162 you if you say C<perl "-V:startperl">.
166 Command-interpreters on non-Unix systems have rather different ideas
167 on quoting than Unix shells. You'll need to learn the special
168 characters in your command-interpreter (C<*>, C<\> and C<"> are
169 common) and how to protect whitespace and these characters to run
170 one-liners (see B<-e> below).
172 On some systems, you may have to change single-quotes to double ones,
173 which you must I<not> do on Unix or Plan 9 systems. You might also
174 have to change a single % to a %%.
179 perl -e 'print "Hello world\n"'
182 perl -e "print \"Hello world\n\""
185 print "Hello world\n"
186 (then Run "Myscript" or Shift-Command-R)
189 perl -e "print ""Hello world\n"""
191 The problem is that none of this is reliable: it depends on the
192 command and it is entirely possible neither works. If B<4DOS> were
193 the command shell, this would probably work better:
195 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
197 B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in
198 when nobody was looking, but just try to find documentation for its
201 Under the Macintosh, it depends which environment you are using. The MacPerl
202 shell, or MPW, is much like Unix shells in its support for several
203 quoting variants, except that it makes free use of the Macintosh's non-ASCII
204 characters as control characters.
206 There is no general solution to all of this. It's just a mess.
208 =head2 Location of Perl
210 It may seem obvious to say, but Perl is useful only when users can
211 easily find it. When possible, it's good for both F</usr/bin/perl>
212 and F</usr/local/bin/perl> to be symlinks to the actual binary. If
213 that can't be done, system administrators are strongly encouraged
214 to put (symlinks to) perl and its accompanying utilities into a
215 directory typically found along a user's PATH, or in some other
216 obvious and convenient place.
218 In this documentation, C<#!/usr/bin/perl> on the first line of the program
219 will stand in for whatever method works on your system. You are
220 advised to use a specific path if you care about a specific version.
222 #!/usr/local/bin/perl5.00554
224 or if you just want to be running at least version, place a statement
225 like this at the top of your program:
229 =head2 Command Switches
231 As with all standard commands, a single-character switch may be
232 clustered with the following switch, if any.
234 #!/usr/bin/perl -spi.orig # same as -s -p -i.orig
240 =item B<-0>[I<octal/hexadecimal>]
242 specifies the input record separator (C<$/>) as an octal or
243 hexadecimal number. If there are no digits, the null character is the
244 separator. Other switches may precede or follow the digits. For
245 example, if you have a version of B<find> which can print filenames
246 terminated by the null character, you can say this:
248 find . -name '*.orig' -print0 | perl -n0e unlink
250 The special value 00 will cause Perl to slurp files in paragraph mode.
251 The value 0777 will cause Perl to slurp files whole because there is no
252 legal byte with that value.
254 If you want to specify any Unicode character, use the hexadecimal
255 format: C<-0xHHH...>, where the C<H> are valid hexadecimal digits.
256 (This means that you cannot use the C<-x> with a directory name that
257 consists of hexadecimal digits.)
259 =item B<-A [I<assertions>]>
261 Activates the assertions given after the switch as a comma-separated
262 list of assertion names. If no assertion name is given, activates all
263 assertions. See L<assertions>.
267 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
268 split command to the @F array is done as the first thing inside the
269 implicit while loop produced by the B<-n> or B<-p>.
271 perl -ane 'print pop(@F), "\n";'
280 An alternate delimiter may be specified using B<-F>.
282 =item B<-C [I<number/list>]>
284 The C<-C> flag controls some Unicode of the Perl Unicode features.
286 As of 5.8.1, the C<-C> can be followed either by a number or a list
287 of option letters. The letters, their numeric values, and effects
288 are as follows; listing the letters is equal to summing the numbers.
290 I 1 STDIN is assumed to be in UTF-8
291 O 2 STDOUT will be in UTF-8
292 E 4 STDERR will be in UTF-8
294 i 8 UTF-8 is the default PerlIO layer for input streams
295 o 16 UTF-8 is the default PerlIO layer for output streams
297 A 32 the @ARGV elements are expected to be strings encoded
299 L 64 normally the "IOEioA" are unconditional,
300 the L makes them conditional on the locale environment
301 variables (the LC_ALL, LC_TYPE, and LANG, in the order
302 of decreasing precedence) -- if the variables indicate
303 UTF-8, then the selected "IOEioA" are in effect
305 For example, C<-COE> and C<-C6> will both turn on UTF-8-ness on both
306 STDOUT and STDERR. Repeating letters is just redundant, not cumulative
309 The C<io> options mean that any subsequent open() (or similar I/O
310 operations) will have the C<:utf8> PerlIO layer implicitly applied
311 to them, in other words, UTF-8 is expected from any input stream,
312 and UTF-8 is produced to any output stream. This is just the default,
313 with explicit layers in open() and with binmode() one can manipulate
316 C<-C> on its own (not followed by any number or option list), or the
317 empty string C<""> for the C<PERL_UNICODE> environment variable, has the
318 same effect as C<-CSDL>. In other words, the standard I/O handles and
319 the default C<open()> layer are UTF-8-fied B<but> only if the locale
320 environment variables indicate a UTF-8 locale. This behaviour follows
321 the I<implicit> (and problematic) UTF-8 behaviour of Perl 5.8.0.
323 You can use C<-C0> (or C<"0"> for C<PERL_UNICODE>) to explicitly
324 disable all the above Unicode features.
326 The read-only magic variable C<${^UNICODE}> reflects the numeric value
327 of this setting. This is variable is set during Perl startup and is
328 thereafter read-only. If you want runtime effects, use the three-arg
329 open() (see L<perlfunc/open>), the two-arg binmode() (see L<perlfunc/binmode>),
330 and the C<open> pragma (see L<open>).
332 (In Perls earlier than 5.8.1 the C<-C> switch was a Win32-only switch
333 that enabled the use of Unicode-aware "wide system call" Win32 APIs.
334 This feature was practically unused, however, and the command line
335 switch was therefore "recycled".)
339 causes Perl to check the syntax of the program and then exit without
340 executing it. Actually, it I<will> execute C<BEGIN>, C<CHECK>, and
341 C<use> blocks, because these are considered as occurring outside the
342 execution of your program. C<INIT> and C<END> blocks, however, will
349 runs the program under the Perl debugger. See L<perldebug>.
350 If B<t> is specified, it indicates to the debugger that threads
351 will be used in the code being debugged.
353 =item B<-d:>I<foo[=bar,baz]>
355 =item B<-dt:>I<foo[=bar,baz]>
357 runs the program under the control of a debugging, profiling, or
358 tracing module installed as Devel::foo. E.g., B<-d:DProf> executes
359 the program using the Devel::DProf profiler. As with the B<-M>
360 flag, options may be passed to the Devel::foo package where they
361 will be received and interpreted by the Devel::foo::import routine.
362 The comma-separated list of options must follow a C<=> character.
363 If B<t> is specified, it indicates to the debugger that threads
364 will be used in the code being debugged.
367 =item B<-D>I<letters>
371 sets debugging flags. To watch how it executes your program, use
372 B<-Dtls>. (This works only if debugging is compiled into your
373 Perl.) Another nice value is B<-Dx>, which lists your compiled
374 syntax tree. And B<-Dr> displays compiled regular expressions;
375 the format of the output is explained in L<perldebguts>.
377 As an alternative, specify a number instead of list of letters (e.g.,
378 B<-D14> is equivalent to B<-Dtls>):
380 1 p Tokenizing and parsing (with v, displays parse stack)
381 2 s Stack snapshots (with v, displays all stacks)
382 4 l Context (loop) stack processing
384 16 o Method and overloading resolution
385 32 c String/numeric conversions
386 64 P Print profiling info, preprocessor command for -P, source file input state
387 128 m Memory allocation
388 256 f Format processing
389 512 r Regular expression parsing and execution
390 1024 x Syntax tree dump
391 2048 u Tainting checks
392 4096 (Obsolete, previously used for LEAKTEST)
393 8192 H Hash dump -- usurps values()
394 16384 X Scratchpad allocation
396 65536 S Thread synchronization
398 262144 R Include reference counts of dumped variables (eg when using -Ds)
399 524288 J Do not s,t,P-debug (Jump over) opcodes within package DB
400 1048576 v Verbose: use in conjunction with other flags
401 2097152 C Copy On Write
402 4194304 A Consistency checks on internal structures
403 8388608 q quiet - currently only suppresses the "EXECUTING" message
405 All these flags require B<-DDEBUGGING> when you compile the Perl
406 executable (but see L<Devel::Peek>, L<re> which may change this).
407 See the F<INSTALL> file in the Perl source distribution
408 for how to do this. This flag is automatically set if you include B<-g>
409 option when C<Configure> asks you about optimizer/debugger flags.
411 If you're just trying to get a print out of each line of Perl code
412 as it executes, the way that C<sh -x> provides for shell scripts,
413 you can't use Perl's B<-D> switch. Instead do this
415 # If you have "env" utility
416 env PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
418 # Bourne shell syntax
419 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
422 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
424 See L<perldebug> for details and variations.
426 =item B<-e> I<commandline>
428 may be used to enter one line of program. If B<-e> is given, Perl
429 will not look for a filename in the argument list. Multiple B<-e>
430 commands may be given to build up a multi-line script. Make sure
431 to use semicolons where you would in a normal program.
435 Disable executing F<$Config{siteperl}/sitecustomize.pl> at
438 Perl can be built so that it by default will try to execute
439 F<$Config{siteperl}/sitecustomize.pl> at startup. This is a hook that
440 allows the sysadmin to customize how perl behaves. It can for
441 instance be used to add entries to the @INC array to make perl find
442 modules in non-standard locations.
444 =item B<-F>I<pattern>
446 specifies the pattern to split on if B<-a> is also in effect. The
447 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
448 put in single quotes.
452 prints a summary of the options.
454 =item B<-i>[I<extension>]
456 specifies that files processed by the C<E<lt>E<gt>> construct are to be
457 edited in-place. It does this by renaming the input file, opening the
458 output file by the original name, and selecting that output file as the
459 default for print() statements. The extension, if supplied, is used to
460 modify the name of the old file to make a backup copy, following these
463 If no extension is supplied, no backup is made and the current file is
466 If the extension doesn't contain a C<*>, then it is appended to the
467 end of the current filename as a suffix. If the extension does
468 contain one or more C<*> characters, then each C<*> is replaced
469 with the current filename. In Perl terms, you could think of this
472 ($backup = $extension) =~ s/\*/$file_name/g;
474 This allows you to add a prefix to the backup file, instead of (or in
475 addition to) a suffix:
477 $ perl -pi'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
479 Or even to place backup copies of the original files into another
480 directory (provided the directory already exists):
482 $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
484 These sets of one-liners are equivalent:
486 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
487 $ perl -pi'*' -e 's/bar/baz/' fileA # overwrite current file
489 $ perl -pi'.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
490 $ perl -pi'*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
492 From the shell, saying
494 $ perl -p -i.orig -e "s/foo/bar/; ... "
496 is the same as using the program:
498 #!/usr/bin/perl -pi.orig
501 which is equivalent to
504 $extension = '.orig';
506 if ($ARGV ne $oldargv) {
507 if ($extension !~ /\*/) {
508 $backup = $ARGV . $extension;
511 ($backup = $extension) =~ s/\*/$ARGV/g;
513 rename($ARGV, $backup);
514 open(ARGVOUT, ">$ARGV");
521 print; # this prints to original filename
525 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
526 know when the filename has changed. It does, however, use ARGVOUT for
527 the selected filehandle. Note that STDOUT is restored as the default
528 output filehandle after the loop.
530 As shown above, Perl creates the backup file whether or not any output
531 is actually changed. So this is just a fancy way to copy files:
533 $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
535 $ perl -p -i'.orig' -e 1 file1 file2 file3...
537 You can use C<eof> without parentheses to locate the end of each input
538 file, in case you want to append to each file, or reset line numbering
539 (see example in L<perlfunc/eof>).
541 If, for a given file, Perl is unable to create the backup file as
542 specified in the extension then it will skip that file and continue on
543 with the next one (if it exists).
545 For a discussion of issues surrounding file permissions and B<-i>,
546 see L<perlfaq5/Why does Perl let me delete read-only files? Why does -i clobber protected files? Isn't this a bug in Perl?>.
548 You cannot use B<-i> to create directories or to strip extensions from
551 Perl does not expand C<~> in filenames, which is good, since some
552 folks use it for their backup files:
554 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
556 Note that because B<-i> renames or deletes the original file before
557 creating a new file of the same name, UNIX-style soft and hard links will
560 Finally, the B<-i> switch does not impede execution when no
561 files are given on the command line. In this case, no backup is made
562 (the original file cannot, of course, be determined) and processing
563 proceeds from STDIN to STDOUT as might be expected.
565 =item B<-I>I<directory>
567 Directories specified by B<-I> are prepended to the search path for
568 modules (C<@INC>), and also tells the C preprocessor where to search for
569 include files. The C preprocessor is invoked with B<-P>; by default it
570 searches /usr/include and /usr/lib/perl.
572 =item B<-l>[I<octnum>]
574 enables automatic line-ending processing. It has two separate
575 effects. First, it automatically chomps C<$/> (the input record
576 separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
577 (the output record separator) to have the value of I<octnum> so
578 that any print statements will have that separator added back on.
579 If I<octnum> is omitted, sets C<$\> to the current value of
580 C<$/>. For instance, to trim lines to 80 columns:
582 perl -lpe 'substr($_, 80) = ""'
584 Note that the assignment C<$\ = $/> is done when the switch is processed,
585 so the input record separator can be different than the output record
586 separator if the B<-l> switch is followed by a B<-0> switch:
588 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
590 This sets C<$\> to newline and then sets C<$/> to the null character.
592 =item B<-m>[B<->]I<module>
594 =item B<-M>[B<->]I<module>
596 =item B<-M>[B<->]I<'module ...'>
598 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
600 B<-m>I<module> executes C<use> I<module> C<();> before executing your
603 B<-M>I<module> executes C<use> I<module> C<;> before executing your
604 program. You can use quotes to add extra code after the module name,
605 e.g., C<'-Mmodule qw(foo bar)'>.
607 If the first character after the B<-M> or B<-m> is a dash (C<->)
608 then the 'use' is replaced with 'no'.
610 A little builtin syntactic sugar means you can also say
611 B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
612 C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
613 importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
614 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
615 removes the distinction between B<-m> and B<-M>.
619 causes Perl to assume the following loop around your program, which
620 makes it iterate over filename arguments somewhat like B<sed -n> or
625 ... # your program goes here
628 Note that the lines are not printed by default. See B<-p> to have
629 lines printed. If a file named by an argument cannot be opened for
630 some reason, Perl warns you about it and moves on to the next file.
632 Here is an efficient way to delete all files that haven't been modified for
635 find . -mtime +7 -print | perl -nle unlink
637 This is faster than using the B<-exec> switch of B<find> because you don't
638 have to start a process on every filename found. It does suffer from
639 the bug of mishandling newlines in pathnames, which you can fix if
640 you follow the example under B<-0>.
642 C<BEGIN> and C<END> blocks may be used to capture control before or after
643 the implicit program loop, just as in B<awk>.
647 causes Perl to assume the following loop around your program, which
648 makes it iterate over filename arguments somewhat like B<sed>:
653 ... # your program goes here
655 print or die "-p destination: $!\n";
658 If a file named by an argument cannot be opened for some reason, Perl
659 warns you about it, and moves on to the next file. Note that the
660 lines are printed automatically. An error occurring during printing is
661 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
662 overrides a B<-n> switch.
664 C<BEGIN> and C<END> blocks may be used to capture control before or after
665 the implicit loop, just as in B<awk>.
669 B<NOTE: Use of -P is strongly discouraged because of its inherent
670 problems, including poor portability.>
672 This option causes your program to be run through the C preprocessor before
673 compilation by Perl. Because both comments and B<cpp> directives begin
674 with the # character, you should avoid starting comments with any words
675 recognized by the C preprocessor such as C<"if">, C<"else">, or C<"define">.
677 If you're considering using C<-P>, you might also want to look at the
678 Filter::cpp module from CPAN.
680 The problems of -P include, but are not limited to:
686 The C<#!> line is stripped, so any switches there don't apply.
690 A C<-P> on a C<#!> line doesn't work.
694 B<All> lines that begin with (whitespace and) a C<#> but
695 do not look like cpp commands, are stripped, including anything
696 inside Perl strings, regular expressions, and here-docs .
700 In some platforms the C preprocessor knows too much: it knows about
701 the C++ -style until-end-of-line comments starting with C<"//">.
702 This will cause problems with common Perl constructs like
706 because after -P this will became illegal code
710 The workaround is to use some other quoting separator than C<"/">,
711 like for example C<"!">:
719 It requires not only a working C preprocessor but also a working
720 F<sed>. If not on UNIX, you are probably out of luck on this.
724 Script line numbers are not preserved.
728 The C<-x> does not work with C<-P>.
734 enables rudimentary switch parsing for switches on the command
735 line after the program name but before any filename arguments (or before
736 an argument of B<-->). This means you can have switches with two leading
737 dashes (B<--help>). Any switch found there is removed from @ARGV and sets the
738 corresponding variable in the Perl program. The following program
739 prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
740 if it is invoked with B<-xyz=abc>.
743 if ($xyz) { print "$xyz\n" }
745 Do note that B<--help> creates the variable ${-help}, which is not compliant
746 with C<strict refs>. Also, when using this option on a script with
747 warnings enabled you may get a lot of spurious "used only once" warnings.
751 makes Perl use the PATH environment variable to search for the
752 program (unless the name of the program contains directory separators).
754 On some platforms, this also makes Perl append suffixes to the
755 filename while searching for it. For example, on Win32 platforms,
756 the ".bat" and ".cmd" suffixes are appended if a lookup for the
757 original name fails, and if the name does not already end in one
758 of those suffixes. If your Perl was compiled with DEBUGGING turned
759 on, using the -Dp switch to Perl shows how the search progresses.
761 Typically this is used to emulate #! startup on platforms that don't
762 support #!. Its also convenient when debugging a script that uses #!,
763 and is thus normally found by the shell's $PATH search mechanism.
765 This example works on many platforms that have a shell compatible with
769 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
770 if $running_under_some_shell;
772 The system ignores the first line and feeds the program to F</bin/sh>,
773 which proceeds to try to execute the Perl program as a shell script.
774 The shell executes the second line as a normal shell command, and thus
775 starts up the Perl interpreter. On some systems $0 doesn't always
776 contain the full pathname, so the B<-S> tells Perl to search for the
777 program if necessary. After Perl locates the program, it parses the
778 lines and ignores them because the variable $running_under_some_shell
779 is never true. If the program will be interpreted by csh, you will need
780 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
781 embedded spaces (and such) in the argument list. To start up sh rather
782 than csh, some systems may have to replace the #! line with a line
783 containing just a colon, which will be politely ignored by Perl. Other
784 systems can't control that, and need a totally devious construct that
785 will work under any of B<csh>, B<sh>, or Perl, such as the following:
787 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
788 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
789 if $running_under_some_shell;
791 If the filename supplied contains directory separators (i.e., is an
792 absolute or relative pathname), and if that file is not found,
793 platforms that append file extensions will do so and try to look
794 for the file with those extensions added, one by one.
796 On DOS-like platforms, if the program does not contain directory
797 separators, it will first be searched for in the current directory
798 before being searched for on the PATH. On Unix platforms, the
799 program will be searched for strictly on the PATH.
803 Like B<-T>, but taint checks will issue warnings rather than fatal
804 errors. These warnings can be controlled normally with C<no warnings
807 B<NOTE: this is not a substitute for -T.> This is meant only to be
808 used as a temporary development aid while securing legacy code:
809 for real production code and for new secure code written from scratch
810 always use the real B<-T>.
814 forces "taint" checks to be turned on so you can test them. Ordinarily
815 these checks are done only when running setuid or setgid. It's a
816 good idea to turn them on explicitly for programs that run on behalf
817 of someone else whom you might not necessarily trust, such as CGI
818 programs or any internet servers you might write in Perl. See
819 L<perlsec> for details. For security reasons, this option must be
820 seen by Perl quite early; usually this means it must appear early
821 on the command line or in the #! line for systems which support
826 This obsolete switch causes Perl to dump core after compiling your
827 program. You can then in theory take this core dump and turn it
828 into an executable file by using the B<undump> program (not supplied).
829 This speeds startup at the expense of some disk space (which you
830 can minimize by stripping the executable). (Still, a "hello world"
831 executable comes out to about 200K on my machine.) If you want to
832 execute a portion of your program before dumping, use the dump()
833 operator instead. Note: availability of B<undump> is platform
834 specific and may not be available for a specific port of Perl.
836 This switch has been superseded in favor of the new Perl code
837 generator backends to the compiler. See L<B> and L<B::Bytecode>
842 allows Perl to do unsafe operations. Currently the only "unsafe"
843 operations are the unlinking of directories while running as superuser,
844 and running setuid programs with fatal taint checks turned into
845 warnings. Note that the B<-w> switch (or the C<$^W> variable) must
846 be used along with this option to actually I<generate> the
847 taint-check warnings.
851 prints the version and patchlevel of your perl executable.
855 prints summary of the major perl configuration values and the current
858 =item B<-V:>I<configvar>
860 Prints to STDOUT the value of the named configuration variable(s),
861 with multiples when your configvar argument looks like a regex (has
862 non-letters). For example:
865 libc='/lib/libc-2.2.4.so';
867 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
868 libc='/lib/libc-2.2.4.so';
870 libpth='/usr/local/lib /lib /usr/lib';
871 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
873 libc='/lib/libc-2.2.4.so';
877 Additionally, extra colons can be used to control formatting. A
878 trailing colon suppresses the linefeed and terminator ';', allowing
879 you to embed queries into shell commands. (mnemonic: PATH separator
882 $ echo "compression-vars: " `perl -V:z.*: ` " are here !"
883 compression-vars: zcat='' zip='zip' are here !
885 A leading colon removes the 'name=' part of the response, this allows
886 you to map to the name you need. (mnemonic: empty label)
888 $ echo "goodvfork="`./perl -Ilib -V::usevfork`
891 Leading and trailing colons can be used together if you need
892 positional parameter values without the names. Note that in the case
893 below, the PERL_API params are returned in alphabetical order.
895 $ echo building_on `perl -V::osname: -V::PERL_API_.*:` now
896 building_on 'linux' '5' '1' '9' now
900 prints warnings about dubious constructs, such as variable names
901 that are mentioned only once and scalar variables that are used
902 before being set, redefined subroutines, references to undefined
903 filehandles or filehandles opened read-only that you are attempting
904 to write on, values used as a number that doesn't look like numbers,
905 using an array as though it were a scalar, if your subroutines
906 recurse more than 100 deep, and innumerable other things.
908 This switch really just enables the internal C<$^W> variable. You
909 can disable or promote into fatal errors specific warnings using
910 C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
911 See also L<perldiag> and L<perltrap>. A new, fine-grained warning
912 facility is also available if you want to manipulate entire classes
913 of warnings; see L<warnings> or L<perllexwarn>.
917 Enables all warnings regardless of C<no warnings> or C<$^W>.
922 Disables all warnings regardless of C<use warnings> or C<$^W>.
927 =item B<-x> I<directory>
929 tells Perl that the program is embedded in a larger chunk of unrelated
930 ASCII text, such as in a mail message. Leading garbage will be
931 discarded until the first line that starts with #! and contains the
932 string "perl". Any meaningful switches on that line will be applied.
933 If a directory name is specified, Perl will switch to that directory
934 before running the program. The B<-x> switch controls only the
935 disposal of leading garbage. The program must be terminated with
936 C<__END__> if there is trailing garbage to be ignored (the program
937 can process any or all of the trailing garbage via the DATA filehandle
948 Used if chdir has no argument.
952 Used if chdir has no argument and HOME is not set.
956 Used in executing subprocesses, and in finding the program if B<-S> is
961 A list of directories in which to look for Perl library
962 files before looking in the standard library and the current
963 directory. Any architecture-specific directories under the specified
964 locations are automatically included if they exist. If PERL5LIB is not
965 defined, PERLLIB is used. Directories are separated (like in PATH) by
966 a colon on unixish platforms and by a semicolon on Windows (the proper
967 path separator being given by the command C<perl -V:path_sep>).
969 When running taint checks (either because the program was running setuid
970 or setgid, or the B<-T> switch was used), neither variable is used.
971 The program should instead say:
973 use lib "/my/directory";
977 Command-line options (switches). Switches in this variable are taken
978 as if they were on every Perl command line. Only the B<-[DIMUdmtw]>
979 switches are allowed. When running taint checks (because the program
980 was running setuid or setgid, or the B<-T> switch was used), this
981 variable is ignored. If PERL5OPT begins with B<-T>, tainting will be
982 enabled, and any subsequent options ignored.
986 A space (or colon) separated list of PerlIO layers. If perl is built
987 to use PerlIO system for IO (the default) these layers effect perl's IO.
989 It is conventional to start layer names with a colon e.g. C<:perlio> to
990 emphasise their similarity to variable "attributes". But the code that parses
991 layer specification strings (which is also used to decode the PERLIO
992 environment variable) treats the colon as a separator.
994 An unset or empty PERLIO is equivalent to C<:stdio>.
996 The list becomes the default for I<all> perl's IO. Consequently only built-in
997 layers can appear in this list, as external layers (such as :encoding()) need
998 IO in order to load them!. See L<"open pragma"|open> for how to add external
999 encodings as defaults.
1001 The layers that it makes sense to include in the PERLIO environment
1002 variable are briefly summarised below. For more details see L<PerlIO>.
1008 A pseudolayer that turns I<off> the C<:utf8> flag for the layer below.
1009 Unlikely to be useful on its own in the global PERLIO environment variable.
1010 You perhaps were thinking of C<:crlf:bytes> or C<:perlio:bytes>.
1014 A layer which does CRLF to "\n" translation distinguishing "text" and
1015 "binary" files in the manner of MS-DOS and similar operating systems.
1016 (It currently does I<not> mimic MS-DOS as far as treating of Control-Z
1017 as being an end-of-file marker.)
1021 A layer which implements "reading" of files by using C<mmap()> to
1022 make (whole) file appear in the process's address space, and then
1023 using that as PerlIO's "buffer".
1027 This is a re-implementation of "stdio-like" buffering written as a
1028 PerlIO "layer". As such it will call whatever layer is below it for
1029 its operations (typically C<:unix>).
1033 An experimental pseudolayer that removes the topmost layer.
1034 Use with the same care as is reserved for nitroglycerin.
1038 A pseudolayer that manipulates other layers. Applying the C<:raw>
1039 layer is equivalent to calling C<binmode($fh)>. It makes the stream
1040 pass each byte as-is without any translation. In particular CRLF
1041 translation, and/or :utf8 intuited from locale are disabled.
1043 Unlike in the earlier versions of Perl C<:raw> is I<not>
1044 just the inverse of C<:crlf> - other layers which would affect the
1045 binary nature of the stream are also removed or disabled.
1049 This layer provides PerlIO interface by wrapping system's ANSI C "stdio"
1050 library calls. The layer provides both buffering and IO.
1051 Note that C<:stdio> layer does I<not> do CRLF translation even if that
1052 is platforms normal behaviour. You will need a C<:crlf> layer above it
1057 Low level layer which calls C<read>, C<write> and C<lseek> etc.
1061 A pseudolayer that turns on a flag on the layer below to tell perl
1062 that output should be in utf8 and that input should be regarded as
1063 already in utf8 form. May be useful in PERLIO environment
1064 variable to make UTF-8 the default. (To turn off that behaviour
1065 use C<:bytes> layer.)
1069 On Win32 platforms this I<experimental> layer uses native "handle" IO
1070 rather than unix-like numeric file descriptor layer. Known to be
1071 buggy in this release.
1075 On all platforms the default set of layers should give acceptable results.
1077 For UNIX platforms that will equivalent of "unix perlio" or "stdio".
1078 Configure is setup to prefer "stdio" implementation if system's library
1079 provides for fast access to the buffer, otherwise it uses the "unix perlio"
1082 On Win32 the default in this release is "unix crlf". Win32's "stdio"
1083 has a number of bugs/mis-features for perl IO which are somewhat
1084 C compiler vendor/version dependent. Using our own C<crlf> layer as
1085 the buffer avoids those issues and makes things more uniform.
1086 The C<crlf> layer provides CRLF to/from "\n" conversion as well as
1089 This release uses C<unix> as the bottom layer on Win32 and so still uses C
1090 compiler's numeric file descriptor routines. There is an experimental native
1091 C<win32> layer which is expected to be enhanced and should eventually be
1092 the default under Win32.
1096 If set to the name of a file or device then certain operations of PerlIO
1097 sub-system will be logged to that file (opened as append). Typical uses
1100 PERLIO_DEBUG=/dev/tty perl script ...
1102 and Win32 approximate equivalent:
1104 set PERLIO_DEBUG=CON
1107 This functionality is disabled for setuid scripts and for scripts run
1112 A list of directories in which to look for Perl library
1113 files before looking in the standard library and the current directory.
1114 If PERL5LIB is defined, PERLLIB is not used.
1118 The command used to load the debugger code. The default is:
1120 BEGIN { require 'perl5db.pl' }
1122 =item PERL5DB_THREADED
1124 If set to a true value, indicates to the debugger that the code being
1125 debugged uses threads.
1127 =item PERL5SHELL (specific to the Win32 port)
1129 May be set to an alternative shell that perl must use internally for
1130 executing "backtick" commands or system(). Default is C<cmd.exe /x/d/c>
1131 on WindowsNT and C<command.com /c> on Windows95. The value is considered
1132 to be space-separated. Precede any character that needs to be protected
1133 (like a space or backslash) with a backslash.
1135 Note that Perl doesn't use COMSPEC for this purpose because
1136 COMSPEC has a high degree of variability among users, leading to
1137 portability concerns. Besides, perl can use a shell that may not be
1138 fit for interactive use, and setting COMSPEC to such a shell may
1139 interfere with the proper functioning of other programs (which usually
1140 look in COMSPEC to find a shell fit for interactive use).
1142 =item PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
1144 Set to 1 to allow the use of non-IFS compatible LSP's.
1145 Perl normally searches for an IFS-compatible LSP because this is required
1146 for its emulation of Windows sockets as real filehandles. However, this may
1147 cause problems if you have a firewall such as McAfee Guardian which requires
1148 all applications to use its LSP which is not IFS-compatible, because clearly
1149 Perl will normally avoid using such an LSP.
1150 Setting this environment variable to 1 means that Perl will simply use the
1151 first suitable LSP enumerated in the catalog, which keeps McAfee Guardian
1152 happy (and in that particular case Perl still works too because McAfee
1153 Guardian's LSP actually plays some other games which allow applications
1154 requiring IFS compatibility to work).
1156 =item PERL_DEBUG_MSTATS
1158 Relevant only if perl is compiled with the malloc included with the perl
1159 distribution (that is, if C<perl -V:d_mymalloc> is 'define').
1160 If set, this causes memory statistics to be dumped after execution. If set
1161 to an integer greater than one, also causes memory statistics to be dumped
1164 =item PERL_DESTRUCT_LEVEL
1166 Relevant only if your perl executable was built with B<-DDEBUGGING>,
1167 this controls the behavior of global destruction of objects and other
1168 references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information.
1170 =item PERL_DL_NONLAZY
1172 Set to one to have perl resolve B<all> undefined symbols when it loads
1173 a dynamic library. The default behaviour is to resolve symbols when
1174 they are used. Setting this variable is useful during testing of
1175 extensions as it ensures that you get an error on misspelled function
1176 names even if the test suite doesn't call it.
1180 If using the C<encoding> pragma without an explicit encoding name, the
1181 PERL_ENCODING environment variable is consulted for an encoding name.
1183 =item PERL_HASH_SEED
1185 (Since Perl 5.8.1.) Used to randomise Perl's internal hash function.
1186 To emulate the pre-5.8.1 behaviour, set to an integer (zero means
1187 exactly the same order as 5.8.0). "Pre-5.8.1" means, among other
1188 things, that hash keys will be ordered the same between different runs
1191 The default behaviour is to randomise unless the PERL_HASH_SEED is set.
1192 If Perl has been compiled with C<-DUSE_HASH_SEED_EXPLICIT>, the default
1193 behaviour is B<not> to randomise unless the PERL_HASH_SEED is set.
1195 If PERL_HASH_SEED is unset or set to a non-numeric string, Perl uses
1196 the pseudorandom seed supplied by the operating system and libraries.
1197 This means that each different run of Perl will have a different
1198 ordering of the results of keys(), values(), and each().
1200 B<Please note that the hash seed is sensitive information>. Hashes are
1201 randomized to protect against local and remote attacks against Perl
1202 code. By manually setting a seed this protection may be partially or
1205 See L<perlsec/"Algorithmic Complexity Attacks"> and
1206 L</PERL_HASH_SEED_DEBUG> for more information.
1208 =item PERL_HASH_SEED_DEBUG
1210 (Since Perl 5.8.1.) Set to one to display (to STDERR) the value of
1211 the hash seed at the beginning of execution. This, combined with
1212 L</PERL_HASH_SEED> is intended to aid in debugging nondeterministic
1213 behavior caused by hash randomization.
1215 B<Note that the hash seed is sensitive information>: by knowing it one
1216 can craft a denial-of-service attack against Perl code, even remotely,
1217 see L<perlsec/"Algorithmic Complexity Attacks"> for more information.
1218 B<Do not disclose the hash seed> to people who don't need to know it.
1219 See also hash_seed() of L<Hash::Util>.
1221 =item PERL_ROOT (specific to the VMS port)
1223 A translation concealed rooted logical name that contains perl and the
1224 logical device for the @INC path on VMS only. Other logical names that
1225 affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and
1226 SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in
1227 L<perlvms> and in F<README.vms> in the Perl source distribution.
1231 In Perls 5.8.1 and later. If set to C<unsafe> the pre-Perl-5.8.0
1232 signals behaviour (immediate but unsafe) is restored. If set to
1233 C<safe> the safe (or deferred) signals are used.
1234 See L<perlipc/"Deferred Signals (Safe Signals)">.
1238 Equivalent to the B<-C> command-line switch. Note that this is not
1239 a boolean variable-- setting this to C<"1"> is not the right way to
1240 "enable Unicode" (whatever that would mean). You can use C<"0"> to
1241 "disable Unicode", though (or alternatively unset PERL_UNICODE in
1242 your shell before starting Perl). See the description of the C<-C>
1243 switch for more information.
1245 =item SYS$LOGIN (specific to the VMS port)
1247 Used if chdir has no argument and HOME and LOGDIR are not set.
1251 Perl also has environment variables that control how Perl handles data
1252 specific to particular natural languages. See L<perllocale>.
1254 Apart from these, Perl uses no other environment variables, except
1255 to make them available to the program being executed, and to child
1256 processes. However, programs running setuid would do well to execute
1257 the following lines before doing anything else, just to keep people
1260 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
1261 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
1262 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};