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>[: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 A Macintosh perl program will have the appropriate Creator and
145 Type, so that double-clicking them will invoke the perl application.
151 $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
152 $ exit++ + ++$status != 0 and $exit = $status = undef;
154 at the top of your program, where B<-mysw> are any command line switches you
155 want to pass to Perl. You can now invoke the program directly, by saying
156 C<perl program>, or as a DCL procedure, by saying C<@program> (or implicitly
157 via F<DCL$PATH> by just using the name of the program).
159 This incantation is a bit much to remember, but Perl will display it for
160 you if you say C<perl "-V:startperl">.
164 Command-interpreters on non-Unix systems have rather different ideas
165 on quoting than Unix shells. You'll need to learn the special
166 characters in your command-interpreter (C<*>, C<\> and C<"> are
167 common) and how to protect whitespace and these characters to run
168 one-liners (see B<-e> below).
170 On some systems, you may have to change single-quotes to double ones,
171 which you must I<not> do on Unix or Plan 9 systems. You might also
172 have to change a single % to a %%.
177 perl -e 'print "Hello world\n"'
180 perl -e "print \"Hello world\n\""
183 print "Hello world\n"
184 (then Run "Myscript" or Shift-Command-R)
187 perl -e "print ""Hello world\n"""
189 The problem is that none of this is reliable: it depends on the
190 command and it is entirely possible neither works. If B<4DOS> were
191 the command shell, this would probably work better:
193 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
195 B<CMD.EXE> in Windows NT slipped a lot of standard Unix functionality in
196 when nobody was looking, but just try to find documentation for its
199 Under the Macintosh, it depends which environment you are using. The MacPerl
200 shell, or MPW, is much like Unix shells in its support for several
201 quoting variants, except that it makes free use of the Macintosh's non-ASCII
202 characters as control characters.
204 There is no general solution to all of this. It's just a mess.
206 =head2 Location of Perl
208 It may seem obvious to say, but Perl is useful only when users can
209 easily find it. When possible, it's good for both F</usr/bin/perl>
210 and F</usr/local/bin/perl> to be symlinks to the actual binary. If
211 that can't be done, system administrators are strongly encouraged
212 to put (symlinks to) perl and its accompanying utilities into a
213 directory typically found along a user's PATH, or in some other
214 obvious and convenient place.
216 In this documentation, C<#!/usr/bin/perl> on the first line of the program
217 will stand in for whatever method works on your system. You are
218 advised to use a specific path if you care about a specific version.
220 #!/usr/local/bin/perl5.00554
222 or if you just want to be running at least version, place a statement
223 like this at the top of your program:
227 =head2 Command Switches
229 As with all standard commands, a single-character switch may be
230 clustered with the following switch, if any.
232 #!/usr/bin/perl -spi.orig # same as -s -p -i.orig
238 =item B<-0>[I<octal/hexadecimal>]
240 specifies the input record separator (C<$/>) as an octal or
241 hexadecimal number. If there are no digits, the null character is the
242 separator. Other switches may precede or follow the digits. For
243 example, if you have a version of B<find> which can print filenames
244 terminated by the null character, you can say this:
246 find . -name '*.orig' -print0 | perl -n0e unlink
248 The special value 00 will cause Perl to slurp files in paragraph mode.
249 The value 0777 will cause Perl to slurp files whole because there is no
250 legal byte with that value.
252 If you want to specify any Unicode character, use the hexadecimal
253 format: C<-0xHHH...>, where the C<H> are valid hexadecimal digits.
254 (This means that you cannot use the C<-x> with a directory name that
255 consists of hexadecimal digits.)
257 =item B<-A [I<assertions>]>
259 Activates the assertions given after the switch as a comma-separated
260 list of assertion names. If no assertion name is given, activates all
261 assertions. See L<assertions>.
265 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
266 split command to the @F array is done as the first thing inside the
267 implicit while loop produced by the B<-n> or B<-p>.
269 perl -ane 'print pop(@F), "\n";'
278 An alternate delimiter may be specified using B<-F>.
280 =item B<-C [I<number/list>]>
282 The C<-C> flag controls some Unicode of the Perl Unicode features.
284 As of 5.8.1, the C<-C> can be followed either by a number or a list
285 of option letters. The letters, their numeric values, and effects
286 are as follows; listing the letters is equal to summing the numbers.
288 I 1 STDIN is assumed to be in UTF-8
289 O 2 STDOUT will be in UTF-8
290 E 4 STDERR will be in UTF-8
292 i 8 UTF-8 is the default PerlIO layer for input streams
293 o 16 UTF-8 is the default PerlIO layer for output streams
295 A 32 the @ARGV elements are expected to be strings encoded
297 L 64 normally the "IOEioA" are unconditional,
298 the L makes them conditional on the locale environment
299 variables (the LC_ALL, LC_TYPE, and LANG, in the order
300 of decreasing precedence) -- if the variables indicate
301 UTF-8, then the selected "IOEioA" are in effect
303 For example, C<-COE> and C<-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) will have the C<:utf8> PerlIO layer implicitly applied
309 to them, in other words, UTF-8 is expected from any input stream,
310 and UTF-8 is produced to any output stream. This is just the default,
311 with explicit layers in open() and with binmode() one can manipulate
314 C<-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 C<-CSDL>. In other words, the standard I/O handles and
317 the default C<open()> layer are UTF-8-fied B<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.
321 You can use C<-C0> (or C<"0"> for C<PERL_UNICODE>) to explicitly
322 disable all the above Unicode features.
324 The read-only magic variable C<${^UNICODE}> reflects the numeric value
325 of this setting. This is variable is set during Perl startup and is
326 thereafter read-only. If you want runtime effects, use the three-arg
327 open() (see L<perlfunc/open>), the two-arg binmode() (see L<perlfunc/binmode>),
328 and the C<open> pragma (see L<open>).
330 (In Perls earlier than 5.8.1 the C<-C> switch was a Win32-only switch
331 that enabled the use of Unicode-aware "wide system call" Win32 APIs.
332 This feature was practically unused, however, and the command line
333 switch was therefore "recycled".)
337 causes Perl to check the syntax of the program and then exit without
338 executing it. Actually, it I<will> execute C<BEGIN>, C<CHECK>, and
339 C<use> blocks, because these are considered as occurring outside the
340 execution of your program. C<INIT> and C<END> blocks, however, will
345 runs the program under the Perl debugger. See L<perldebug>.
347 =item B<-d:>I<foo[=bar,baz]>
349 runs the program under the control of a debugging, profiling, or
350 tracing module installed as Devel::foo. E.g., B<-d:DProf> executes
351 the program using the Devel::DProf profiler. As with the B<-M>
352 flag, options may be passed to the Devel::foo package where they
353 will be received and interpreted by the Devel::foo::import routine.
354 The comma-separated list of options must follow a C<=> character.
357 =item B<-D>I<letters>
361 sets debugging flags. To watch how it executes your program, use
362 B<-Dtls>. (This works only if debugging is compiled into your
363 Perl.) Another nice value is B<-Dx>, which lists your compiled
364 syntax tree. And B<-Dr> displays compiled regular expressions;
365 the format of the output is explained in L<perldebguts>.
367 As an alternative, specify a number instead of list of letters (e.g.,
368 B<-D14> is equivalent to B<-Dtls>):
370 1 p Tokenizing and parsing (with v, displays parse stack)
371 2 s Stack snapshots (with v, displays all stacks)
372 4 l Context (loop) stack processing
374 16 o Method and overloading resolution
375 32 c String/numeric conversions
376 64 P Print profiling info, preprocessor command for -P, source file input state
377 128 m Memory allocation
378 256 f Format processing
379 512 r Regular expression parsing and execution
380 1024 x Syntax tree dump
381 2048 u Tainting checks
382 4096 (Obsolete, previously used for LEAKTEST)
383 8192 H Hash dump -- usurps values()
384 16384 X Scratchpad allocation
386 65536 S Thread synchronization
388 262144 R Include reference counts of dumped variables (eg when using -Ds)
389 524288 J Do not s,t,P-debug (Jump over) opcodes within package DB
390 1048576 v Verbose: use in conjunction with other flags
391 2097152 C Copy On Write
392 4194304 A Consistency checks on internal structures
393 8388608 q quiet - currently only suppresses the "EXECUTING" message
395 All these flags require B<-DDEBUGGING> when you compile the Perl
396 executable (but see L<Devel::Peek>, L<re> which may change this).
397 See the F<INSTALL> file in the Perl source distribution
398 for how to do this. This flag is automatically set if you include B<-g>
399 option when C<Configure> asks you about optimizer/debugger flags.
401 If you're just trying to get a print out of each line of Perl code
402 as it executes, the way that C<sh -x> provides for shell scripts,
403 you can't use Perl's B<-D> switch. Instead do this
405 # If you have "env" utility
406 env=PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
408 # Bourne shell syntax
409 $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
412 % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
414 See L<perldebug> for details and variations.
416 =item B<-e> I<commandline>
418 may be used to enter one line of program. If B<-e> is given, Perl
419 will not look for a filename in the argument list. Multiple B<-e>
420 commands may be given to build up a multi-line script. Make sure
421 to use semicolons where you would in a normal program.
423 =item B<-F>I<pattern>
425 specifies the pattern to split on if B<-a> is also in effect. The
426 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
427 put in single quotes.
431 prints a summary of the options.
433 =item B<-i>[I<extension>]
435 specifies that files processed by the C<E<lt>E<gt>> construct are to be
436 edited in-place. It does this by renaming the input file, opening the
437 output file by the original name, and selecting that output file as the
438 default for print() statements. The extension, if supplied, is used to
439 modify the name of the old file to make a backup copy, following these
442 If no extension is supplied, no backup is made and the current file is
445 If the extension doesn't contain a C<*>, then it is appended to the
446 end of the current filename as a suffix. If the extension does
447 contain one or more C<*> characters, then each C<*> is replaced
448 with the current filename. In Perl terms, you could think of this
451 ($backup = $extension) =~ s/\*/$file_name/g;
453 This allows you to add a prefix to the backup file, instead of (or in
454 addition to) a suffix:
456 $ perl -pi'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
458 Or even to place backup copies of the original files into another
459 directory (provided the directory already exists):
461 $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
463 These sets of one-liners are equivalent:
465 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
466 $ perl -pi'*' -e 's/bar/baz/' fileA # overwrite current file
468 $ perl -pi'.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
469 $ perl -pi'*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
471 From the shell, saying
473 $ perl -p -i.orig -e "s/foo/bar/; ... "
475 is the same as using the program:
477 #!/usr/bin/perl -pi.orig
480 which is equivalent to
483 $extension = '.orig';
485 if ($ARGV ne $oldargv) {
486 if ($extension !~ /\*/) {
487 $backup = $ARGV . $extension;
490 ($backup = $extension) =~ s/\*/$ARGV/g;
492 rename($ARGV, $backup);
493 open(ARGVOUT, ">$ARGV");
500 print; # this prints to original filename
504 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
505 know when the filename has changed. It does, however, use ARGVOUT for
506 the selected filehandle. Note that STDOUT is restored as the default
507 output filehandle after the loop.
509 As shown above, Perl creates the backup file whether or not any output
510 is actually changed. So this is just a fancy way to copy files:
512 $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
514 $ perl -p -i'.orig' -e 1 file1 file2 file3...
516 You can use C<eof> without parentheses to locate the end of each input
517 file, in case you want to append to each file, or reset line numbering
518 (see example in L<perlfunc/eof>).
520 If, for a given file, Perl is unable to create the backup file as
521 specified in the extension then it will skip that file and continue on
522 with the next one (if it exists).
524 For a discussion of issues surrounding file permissions and B<-i>,
525 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?>.
527 You cannot use B<-i> to create directories or to strip extensions from
530 Perl does not expand C<~> in filenames, which is good, since some
531 folks use it for their backup files:
533 $ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
535 Note that because B<-i> renames or deletes the original file before
536 creating a new file of the same name, UNIX-style soft and hard links will
539 Finally, the B<-i> switch does not impede execution when no
540 files are given on the command line. In this case, no backup is made
541 (the original file cannot, of course, be determined) and processing
542 proceeds from STDIN to STDOUT as might be expected.
544 =item B<-I>I<directory>
546 Directories specified by B<-I> are prepended to the search path for
547 modules (C<@INC>), and also tells the C preprocessor where to search for
548 include files. The C preprocessor is invoked with B<-P>; by default it
549 searches /usr/include and /usr/lib/perl.
551 =item B<-l>[I<octnum>]
553 enables automatic line-ending processing. It has two separate
554 effects. First, it automatically chomps C<$/> (the input record
555 separator) when used with B<-n> or B<-p>. Second, it assigns C<$\>
556 (the output record separator) to have the value of I<octnum> so
557 that any print statements will have that separator added back on.
558 If I<octnum> is omitted, sets C<$\> to the current value of
559 C<$/>. For instance, to trim lines to 80 columns:
561 perl -lpe 'substr($_, 80) = ""'
563 Note that the assignment C<$\ = $/> is done when the switch is processed,
564 so the input record separator can be different than the output record
565 separator if the B<-l> switch is followed by a B<-0> switch:
567 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
569 This sets C<$\> to newline and then sets C<$/> to the null character.
571 =item B<-m>[B<->]I<module>
573 =item B<-M>[B<->]I<module>
575 =item B<-M>[B<->]I<'module ...'>
577 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
579 B<-m>I<module> executes C<use> I<module> C<();> before executing your
582 B<-M>I<module> executes C<use> I<module> C<;> before executing your
583 program. You can use quotes to add extra code after the module name,
584 e.g., C<'-Mmodule qw(foo bar)'>.
586 If the first character after the B<-M> or B<-m> is a dash (C<->)
587 then the 'use' is replaced with 'no'.
589 A little builtin syntactic sugar means you can also say
590 B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
591 C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
592 importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
593 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
594 removes the distinction between B<-m> and B<-M>.
598 causes Perl to assume the following loop around your program, which
599 makes it iterate over filename arguments somewhat like B<sed -n> or
604 ... # your program goes here
607 Note that the lines are not printed by default. See B<-p> to have
608 lines printed. If a file named by an argument cannot be opened for
609 some reason, Perl warns you about it and moves on to the next file.
611 Here is an efficient way to delete all files that haven't been modifed for
614 find . -mtime +7 -print | perl -nle unlink
616 This is faster than using the B<-exec> switch of B<find> because you don't
617 have to start a process on every filename found. It does suffer from
618 the bug of mishandling newlines in pathnames, which you can fix if
619 you follow the example under B<-0>.
621 C<BEGIN> and C<END> blocks may be used to capture control before or after
622 the implicit program loop, just as in B<awk>.
626 causes Perl to assume the following loop around your program, which
627 makes it iterate over filename arguments somewhat like B<sed>:
632 ... # your program goes here
634 print or die "-p destination: $!\n";
637 If a file named by an argument cannot be opened for some reason, Perl
638 warns you about it, and moves on to the next file. Note that the
639 lines are printed automatically. An error occurring during printing is
640 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
641 overrides a B<-n> switch.
643 C<BEGIN> and C<END> blocks may be used to capture control before or after
644 the implicit loop, just as in B<awk>.
648 B<NOTE: Use of -P is strongly discouraged because of its inherent
649 problems, including poor portability.>
651 This option causes your program to be run through the C preprocessor before
652 compilation by Perl. Because both comments and B<cpp> directives begin
653 with the # character, you should avoid starting comments with any words
654 recognized by the C preprocessor such as C<"if">, C<"else">, or C<"define">.
656 If you're considering using C<-P>, you might also want to look at the
657 Filter::cpp module from CPAN.
659 The problems of -P include, but are not limited to:
665 The C<#!> line is stripped, so any switches there don't apply.
669 A C<-P> on a C<#!> line doesn't work.
673 B<All> lines that begin with (whitespace and) a C<#> but
674 do not look like cpp commands, are stripped, including anything
675 inside Perl strings, regular expressions, and here-docs .
679 In some platforms the C preprocessor knows too much: it knows about
680 the C++ -style until-end-of-line comments starting with C<"//">.
681 This will cause problems with common Perl constructs like
685 because after -P this will became illegal code
689 The workaround is to use some other quoting separator than C<"/">,
690 like for example C<"!">:
698 It requires not only a working C preprocessor but also a working
699 F<sed>. If not on UNIX, you are probably out of luck on this.
703 Script line numbers are not preserved.
707 The C<-x> does not work with C<-P>.
713 enables rudimentary switch parsing for switches on the command
714 line after the program name but before any filename arguments (or before
715 an argument of B<-->). This means you can have switches with two leading
716 dashes (B<--help>). Any switch found there is removed from @ARGV and sets the
717 corresponding variable in the Perl program. The following program
718 prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
719 if it is invoked with B<-xyz=abc>.
722 if ($xyz) { print "$xyz\n" }
724 Do note that B<--help> creates the variable ${-help}, which is not compliant
729 makes Perl use the PATH environment variable to search for the
730 program (unless the name of the program contains directory separators).
732 On some platforms, this also makes Perl append suffixes to the
733 filename while searching for it. For example, on Win32 platforms,
734 the ".bat" and ".cmd" suffixes are appended if a lookup for the
735 original name fails, and if the name does not already end in one
736 of those suffixes. If your Perl was compiled with DEBUGGING turned
737 on, using the -Dp switch to Perl shows how the search progresses.
739 Typically this is used to emulate #! startup on platforms that don't
740 support #!. Its also convenient when debugging a script that uses #!,
741 and is thus normally found by the shell's $PATH search mechanism.
743 This example works on many platforms that have a shell compatible with
747 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
748 if $running_under_some_shell;
750 The system ignores the first line and feeds the program to F</bin/sh>,
751 which proceeds to try to execute the Perl program as a shell script.
752 The shell executes the second line as a normal shell command, and thus
753 starts up the Perl interpreter. On some systems $0 doesn't always
754 contain the full pathname, so the B<-S> tells Perl to search for the
755 program if necessary. After Perl locates the program, it parses the
756 lines and ignores them because the variable $running_under_some_shell
757 is never true. If the program will be interpreted by csh, you will need
758 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
759 embedded spaces (and such) in the argument list. To start up sh rather
760 than csh, some systems may have to replace the #! line with a line
761 containing just a colon, which will be politely ignored by Perl. Other
762 systems can't control that, and need a totally devious construct that
763 will work under any of B<csh>, B<sh>, or Perl, such as the following:
765 eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
766 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
767 if $running_under_some_shell;
769 If the filename supplied contains directory separators (i.e., is an
770 absolute or relative pathname), and if that file is not found,
771 platforms that append file extensions will do so and try to look
772 for the file with those extensions added, one by one.
774 On DOS-like platforms, if the program does not contain directory
775 separators, it will first be searched for in the current directory
776 before being searched for on the PATH. On Unix platforms, the
777 program will be searched for strictly on the PATH.
781 Like B<-T>, but taint checks will issue warnings rather than fatal
782 errors. These warnings can be controlled normally with C<no warnings
785 B<NOTE: this is not a substitute for -T.> This is meant only to be
786 used as a temporary development aid while securing legacy code:
787 for real production code and for new secure code written from scratch
788 always use the real B<-T>.
792 forces "taint" checks to be turned on so you can test them. Ordinarily
793 these checks are done only when running setuid or setgid. It's a
794 good idea to turn them on explicitly for programs that run on behalf
795 of someone else whom you might not necessarily trust, such as CGI
796 programs or any internet servers you might write in Perl. See
797 L<perlsec> for details. For security reasons, this option must be
798 seen by Perl quite early; usually this means it must appear early
799 on the command line or in the #! line for systems which support
804 This obsolete switch causes Perl to dump core after compiling your
805 program. You can then in theory take this core dump and turn it
806 into an executable file by using the B<undump> program (not supplied).
807 This speeds startup at the expense of some disk space (which you
808 can minimize by stripping the executable). (Still, a "hello world"
809 executable comes out to about 200K on my machine.) If you want to
810 execute a portion of your program before dumping, use the dump()
811 operator instead. Note: availability of B<undump> is platform
812 specific and may not be available for a specific port of Perl.
814 This switch has been superseded in favor of the new Perl code
815 generator backends to the compiler. See L<B> and L<B::Bytecode>
820 allows Perl to do unsafe operations. Currently the only "unsafe"
821 operations are the unlinking of directories while running as superuser,
822 and running setuid programs with fatal taint checks turned into
823 warnings. Note that the B<-w> switch (or the C<$^W> variable) must
824 be used along with this option to actually I<generate> the
825 taint-check warnings.
829 prints the version and patchlevel of your perl executable.
833 prints summary of the major perl configuration values and the current
836 =item B<-V:>I<configvar>
838 Prints to STDOUT the value of the named configuration variable(s),
839 with multiples when your configvar argument looks like a regex (has
840 non-letters). For example:
843 libc='/lib/libc-2.2.4.so';
845 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
846 libc='/lib/libc-2.2.4.so';
848 libpth='/usr/local/lib /lib /usr/lib';
849 libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
851 libc='/lib/libc-2.2.4.so';
855 Additionally, extra colons can be used to control formatting. A
856 trailing colon suppresses the linefeed and terminator ';', allowing
857 you to embed queries into shell commands. (mnemonic: PATH separator
860 $ echo "compression-vars: " `perl -V:z.*: ` " are here !"
861 compression-vars: zcat='' zip='zip' are here !
863 A leading colon removes the 'name=' part of the response, this allows
864 you to map to the name you need. (mnemonic: empty label)
866 $ echo "goodvfork="`./perl -Ilib -V::usevfork`
869 Leading and trailing colons can be used together if you need
870 positional parameter values without the names. Note that in the case
871 below, the PERL_API params are returned in alphabetical order.
873 $ echo building_on `perl -V::osname: -V::PERL_API_.*:` now
874 building_on 'linux' '5' '1' '9' now
878 prints warnings about dubious constructs, such as variable names
879 that are mentioned only once and scalar variables that are used
880 before being set, redefined subroutines, references to undefined
881 filehandles or filehandles opened read-only that you are attempting
882 to write on, values used as a number that doesn't look like numbers,
883 using an array as though it were a scalar, if your subroutines
884 recurse more than 100 deep, and innumerable other things.
886 This switch really just enables the internal C<$^W> variable. You
887 can disable or promote into fatal errors specific warnings using
888 C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
889 See also L<perldiag> and L<perltrap>. A new, fine-grained warning
890 facility is also available if you want to manipulate entire classes
891 of warnings; see L<warnings> or L<perllexwarn>.
895 Enables all warnings regardless of C<no warnings> or C<$^W>.
900 Disables all warnings regardless of C<use warnings> or C<$^W>.
905 =item B<-x> I<directory>
907 tells Perl that the program is embedded in a larger chunk of unrelated
908 ASCII text, such as in a mail message. Leading garbage will be
909 discarded until the first line that starts with #! and contains the
910 string "perl". Any meaningful switches on that line will be applied.
911 If a directory name is specified, Perl will switch to that directory
912 before running the program. The B<-x> switch controls only the
913 disposal of leading garbage. The program must be terminated with
914 C<__END__> if there is trailing garbage to be ignored (the program
915 can process any or all of the trailing garbage via the DATA filehandle
926 Used if chdir has no argument.
930 Used if chdir has no argument and HOME is not set.
934 Used in executing subprocesses, and in finding the program if B<-S> is
939 A list of directories in which to look for Perl library
940 files before looking in the standard library and the current
941 directory. Any architecture-specific directories under the specified
942 locations are automatically included if they exist. If PERL5LIB is not
943 defined, PERLLIB is used. Directories are separated (like in PATH) by
944 a colon on unixish platforms and by a semicolon on Windows (the proper
945 path separator being given by the command C<perl -V:path_sep>).
947 When running taint checks (either because the program was running setuid
948 or setgid, or the B<-T> switch was used), neither variable is used.
949 The program should instead say:
951 use lib "/my/directory";
955 Command-line options (switches). Switches in this variable are taken
956 as if they were on every Perl command line. Only the B<-[DIMUdmtw]>
957 switches are allowed. When running taint checks (because the program
958 was running setuid or setgid, or the B<-T> switch was used), this
959 variable is ignored. If PERL5OPT begins with B<-T>, tainting will be
960 enabled, and any subsequent options ignored.
964 A space (or colon) separated list of PerlIO layers. If perl is built
965 to use PerlIO system for IO (the default) these layers effect perl's IO.
967 It is conventional to start layer names with a colon e.g. C<:perlio> to
968 emphasise their similarity to variable "attributes". But the code that parses
969 layer specification strings (which is also used to decode the PERLIO
970 environment variable) treats the colon as a separator.
972 An unset or empty PERLIO is equivalent to C<:stdio>.
974 The list becomes the default for I<all> perl's IO. Consequently only built-in
975 layers can appear in this list, as external layers (such as :encoding()) need
976 IO in order to load them!. See L<"open pragma"|open> for how to add external
977 encodings as defaults.
979 The layers that it makes sense to include in the PERLIO environment
980 variable are briefly summarised below. For more details see L<PerlIO>.
986 A pseudolayer that turns I<off> the C<:utf8> flag for the layer below.
987 Unlikely to be useful on its own in the global PERLIO environment variable.
988 You perhaps were thinking of C<:crlf:bytes> or C<:perlio:bytes>.
992 A layer which does CRLF to "\n" translation distinguishing "text" and
993 "binary" files in the manner of MS-DOS and similar operating systems.
994 (It currently does I<not> mimic MS-DOS as far as treating of Control-Z
995 as being an end-of-file marker.)
999 A layer which implements "reading" of files by using C<mmap()> to
1000 make (whole) file appear in the process's address space, and then
1001 using that as PerlIO's "buffer".
1005 This is a re-implementation of "stdio-like" buffering written as a
1006 PerlIO "layer". As such it will call whatever layer is below it for
1007 its operations (typically C<:unix>).
1011 An experimental pseudolayer that removes the topmost layer.
1012 Use with the same care as is reserved for nitroglycerin.
1016 A pseudolayer that manipulates other layers. Applying the C<:raw>
1017 layer is equivalent to calling C<binmode($fh)>. It makes the stream
1018 pass each byte as-is without any translation. In particular CRLF
1019 translation, and/or :utf8 intuited from locale are disabled.
1021 Unlike in the earlier versions of Perl C<:raw> is I<not>
1022 just the inverse of C<:crlf> - other layers which would affect the
1023 binary nature of the stream are also removed or disabled.
1027 This layer provides PerlIO interface by wrapping system's ANSI C "stdio"
1028 library calls. The layer provides both buffering and IO.
1029 Note that C<:stdio> layer does I<not> do CRLF translation even if that
1030 is platforms normal behaviour. You will need a C<:crlf> layer above it
1035 Low level layer which calls C<read>, C<write> and C<lseek> etc.
1039 A pseudolayer that turns on a flag on the layer below to tell perl
1040 that output should be in utf8 and that input should be regarded as
1041 already in utf8 form. May be useful in PERLIO environment
1042 variable to make UTF-8 the default. (To turn off that behaviour
1043 use C<:bytes> layer.)
1047 On Win32 platforms this I<experimental> layer uses native "handle" IO
1048 rather than unix-like numeric file descriptor layer. Known to be
1049 buggy in this release.
1053 On all platforms the default set of layers should give acceptable results.
1055 For UNIX platforms that will equivalent of "unix perlio" or "stdio".
1056 Configure is setup to prefer "stdio" implementation if system's library
1057 provides for fast access to the buffer, otherwise it uses the "unix perlio"
1060 On Win32 the default in this release is "unix crlf". Win32's "stdio"
1061 has a number of bugs/mis-features for perl IO which are somewhat
1062 C compiler vendor/version dependent. Using our own C<crlf> layer as
1063 the buffer avoids those issues and makes things more uniform.
1064 The C<crlf> layer provides CRLF to/from "\n" conversion as well as
1067 This release uses C<unix> as the bottom layer on Win32 and so still uses C
1068 compiler's numeric file descriptor routines. There is an experimental native
1069 C<win32> layer which is expected to be enhanced and should eventually be
1070 the default under Win32.
1074 If set to the name of a file or device then certain operations of PerlIO
1075 sub-system will be logged to that file (opened as append). Typical uses
1078 PERLIO_DEBUG=/dev/tty perl script ...
1080 and Win32 approximate equivalent:
1082 set PERLIO_DEBUG=CON
1088 A list of directories in which to look for Perl library
1089 files before looking in the standard library and the current directory.
1090 If PERL5LIB is defined, PERLLIB is not used.
1094 The command used to load the debugger code. The default is:
1096 BEGIN { require 'perl5db.pl' }
1098 =item PERL5SHELL (specific to the Win32 port)
1100 May be set to an alternative shell that perl must use internally for
1101 executing "backtick" commands or system(). Default is C<cmd.exe /x/d/c>
1102 on WindowsNT and C<command.com /c> on Windows95. The value is considered
1103 to be space-separated. Precede any character that needs to be protected
1104 (like a space or backslash) with a backslash.
1106 Note that Perl doesn't use COMSPEC for this purpose because
1107 COMSPEC has a high degree of variability among users, leading to
1108 portability concerns. Besides, perl can use a shell that may not be
1109 fit for interactive use, and setting COMSPEC to such a shell may
1110 interfere with the proper functioning of other programs (which usually
1111 look in COMSPEC to find a shell fit for interactive use).
1113 =item PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
1115 Set to 1 to allow the use of non-IFS compatible LSP's.
1116 Perl normally searches for an IFS-compatible LSP because this is required
1117 for its emulation of Windows sockets as real filehandles. However, this may
1118 cause problems if you have a firewall such as McAfee Guardian which requires
1119 all applications to use its LSP which is not IFS-compatible, because clearly
1120 Perl will normally avoid using such an LSP.
1121 Setting this environment variable to 1 means that Perl will simply use the
1122 first suitable LSP enumerated in the catalog, which keeps McAfee Guardian
1123 happy (and in that particular case Perl still works too because McAfee
1124 Guardian's LSP actually plays some other games which allow applications
1125 requiring IFS compatibility to work).
1127 =item PERL_DEBUG_MSTATS
1129 Relevant only if perl is compiled with the malloc included with the perl
1130 distribution (that is, if C<perl -V:d_mymalloc> is 'define').
1131 If set, this causes memory statistics to be dumped after execution. If set
1132 to an integer greater than one, also causes memory statistics to be dumped
1135 =item PERL_DESTRUCT_LEVEL
1137 Relevant only if your perl executable was built with B<-DDEBUGGING>,
1138 this controls the behavior of global destruction of objects and other
1139 references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information.
1141 =item PERL_DL_NONLAZY
1143 Set to one to have perl resolve B<all> undefined symbols when it loads
1144 a dynamic library. The default behaviour is to resolve symbols when
1145 they are used. Setting this variable is useful during testing of
1146 extensions as it ensures that you get an error on misspelled function
1147 names even if the test suite doesn't call it.
1151 If using the C<encoding> pragma without an explicit encoding name, the
1152 PERL_ENCODING environment variable is consulted for an encoding name.
1154 =item PERL_HASH_SEED
1156 (Since Perl 5.8.1.) Used to randomise Perl's internal hash function.
1157 To emulate the pre-5.8.1 behaviour, set to an integer (zero means
1158 exactly the same order as 5.8.0). "Pre-5.8.1" means, among other
1159 things, that hash keys will be ordered the same between different runs
1162 The default behaviour is to randomise unless the PERL_HASH_SEED is set.
1163 If Perl has been compiled with C<-DUSE_HASH_SEED_EXPLICIT>, the default
1164 behaviour is B<not> to randomise unless the PERL_HASH_SEED is set.
1166 If PERL_HASH_SEED is unset or set to a non-numeric string, Perl uses
1167 the pseudorandom seed supplied by the operating system and libraries.
1168 This means that each different run of Perl will have a different
1169 ordering of the results of keys(), values(), and each().
1171 B<Please note that the hash seed is sensitive information>. Hashes are
1172 randomized to protect against local and remote attacks against Perl
1173 code. By manually setting a seed this protection may be partially or
1176 See L<perlsec/"Algorithmic Complexity Attacks"> and
1177 L</PERL_HASH_SEED_DEBUG> for more information.
1179 =item PERL_HASH_SEED_DEBUG
1181 (Since Perl 5.8.1.) Set to one to display (to STDERR) the value of
1182 the hash seed at the beginning of execution. This, combined with
1183 L</PERL_HASH_SEED> is intended to aid in debugging nondeterministic
1184 behavior caused by hash randomization.
1186 B<Note that the hash seed is sensitive information>: by knowing it one
1187 can craft a denial-of-service attack against Perl code, even remotely,
1188 see L<perlsec/"Algorithmic Complexity Attacks"> for more information.
1189 B<Do not disclose the hash seed> to people who don't need to know it.
1190 See also hash_seed() of L<Hash::Util>.
1192 =item PERL_ROOT (specific to the VMS port)
1194 A translation concealed rooted logical name that contains perl and the
1195 logical device for the @INC path on VMS only. Other logical names that
1196 affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and
1197 SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in
1198 L<perlvms> and in F<README.vms> in the Perl source distribution.
1202 In Perls 5.8.1 and later. If set to C<unsafe> the pre-Perl-5.8.0
1203 signals behaviour (immediate but unsafe) is restored. If set to
1204 C<safe> the safe (or deferred) signals are used.
1205 See L<perlipc/"Deferred Signals (Safe signals)">.
1209 Equivalent to the B<-C> command-line switch. Note that this is not
1210 a boolean variable-- setting this to C<"1"> is not the right way to
1211 "enable Unicode" (whatever that would mean). You can use C<"0"> to
1212 "disable Unicode", though (or alternatively unset PERL_UNICODE in
1213 your shell before starting Perl). See the description of the C<-C>
1214 switch for more information.
1216 =item SYS$LOGIN (specific to the VMS port)
1218 Used if chdir has no argument and HOME and LOGDIR are not set.
1222 Perl also has environment variables that control how Perl handles data
1223 specific to particular natural languages. See L<perllocale>.
1225 Apart from these, Perl uses no other environment variables, except
1226 to make them available to the program being executed, and to child
1227 processes. However, programs running setuid would do well to execute
1228 the following lines before doing anything else, just to keep people
1231 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
1232 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
1233 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};