3 perlrun - how to execute the Perl interpreter
7 B<perl> S<[ B<-sTuU> ]>
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>] ]>
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> ]...>
20 Upon startup, Perl looks for your script in one of the following
27 Specified line by line via B<-e> switches on the command line.
31 Contained in the file specified by the first filename on the command line.
32 (Note that systems supporting the #! notation invoke interpreters this
33 way. See L<Location of Perl>.)
37 Passed in implicitly via standard input. This works only if there are
38 no filename arguments--to pass arguments to a STDIN script you
39 must explicitly specify a "-" for the script name.
43 With methods 2 and 3, Perl starts parsing the input file from the
44 beginning, unless you've specified a B<-x> switch, in which case it
45 scans for the first line starting with #! and containing the word
46 "perl", and starts there instead. This is useful for running a script
47 embedded in a larger message. (In this case you would indicate the end
48 of the script using the C<__END__> token.)
50 The #! line is always examined for switches as the line is being
51 parsed. Thus, if you're on a machine that allows only one argument
52 with the #! line, or worse, doesn't even recognize the #! line, you
53 still can get consistent switch behavior regardless of how Perl was
54 invoked, even if B<-x> was used to find the beginning of the script.
56 Because many operating systems silently chop off kernel interpretation of
57 the #! line after 32 characters, some switches may be passed in on the
58 command line, and some may not; you could even get a "-" without its
59 letter, if you're not careful. You probably want to make sure that all
60 your switches fall either before or after that 32 character boundary.
61 Most switches don't actually care if they're processed redundantly, but
62 getting a - instead of a complete switch could cause Perl to try to
63 execute standard input instead of your script. And a partial B<-I> switch
64 could also cause odd results.
66 Some switches do care if they are processed twice, for instance combinations
67 of B<-l> and B<-0>. Either put all the switches after the 32 character
68 boundary (if applicable), or replace the use of B<-0>I<digits> by
69 C<BEGIN{ $/ = "\0digits"; }>.
71 Parsing of the #! switches starts wherever "perl" is mentioned in the line.
72 The sequences "-*" and "- " are specifically ignored so that you could,
73 if you were so inclined, say
75 #!/bin/sh -- # -*- perl -*- -p
76 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
77 if $running_under_some_shell;
79 to let Perl see the B<-p> switch.
81 If the #! line does not contain the word "perl", the program named after
82 the #! is executed instead of the Perl interpreter. This is slightly
83 bizarre, but it helps people on machines that don't do #!, because they
84 can tell a program that their SHELL is /usr/bin/perl, and Perl will then
85 dispatch the program to the correct interpreter for them.
87 After locating your script, Perl compiles the entire script to an
88 internal form. If there are any compilation errors, execution of the
89 script is not attempted. (This is unlike the typical shell script,
90 which might run part-way through before finding a syntax error.)
92 If the script is syntactically correct, it is executed. If the script
93 runs off the end without hitting an exit() or die() operator, an implicit
94 C<exit(0)> is provided to indicate successful completion.
96 =head2 #! and quoting on non-Unix systems
98 Unix's #! technique can be simulated on other systems:
106 extproc perl -S -your_switches
108 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
113 Create a batch file to run your script, and codify it in
114 C<ALTERNATIVE_SHEBANG> (see the F<dosish.h> file in the source
115 distribution for more information).
119 The Win95/NT installation, when using the Activeware port of Perl,
120 will modify the Registry to associate the F<.pl> extension with the perl
121 interpreter. If you install another port of Perl, including the one
122 in the Win32 directory of the Perl distribution, then you'll have to
123 modify the Registry yourself. Note that this means you can no
124 longer tell the difference between an executable Perl program
125 and a Perl library file.
129 Macintosh perl scripts will have the appropriate Creator and
130 Type, so that double-clicking them will invoke the perl application.
134 Command-interpreters on non-Unix systems have rather different ideas
135 on quoting than Unix shells. You'll need to learn the special
136 characters in your command-interpreter (C<*>, C<\> and C<"> are
137 common) and how to protect whitespace and these characters to run
138 one-liners (see C<-e> below).
140 On some systems, you may have to change single-quotes to double ones,
141 which you must I<NOT> do on Unix or Plan9 systems. You might also
142 have to change a single % to a %%.
147 perl -e 'print "Hello world\n"'
150 perl -e "print \"Hello world\n\""
153 print "Hello world\n"
154 (then Run "Myscript" or Shift-Command-R)
157 perl -e "print ""Hello world\n"""
159 The problem is that none of this is reliable: it depends on the command
160 and it is entirely possible neither works. If 4DOS was the command shell, this would
161 probably work better:
163 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
165 CMD.EXE in Windows NT slipped a lot of standard Unix functionality in
166 when nobody was looking, but just try to find documentation for its
169 Under the Macintosh, it depends which environment you are using. The MacPerl
170 shell, or MPW, is much like Unix shells in its support for several
171 quoting variants, except that it makes free use of the Macintosh's non-ASCII
172 characters as control characters.
174 There is no general solution to all of this. It's just a mess.
176 =head2 Location of Perl
178 It may seem obvious to say, but Perl is useful only when users can
179 easily find it. When possible, it's good for both B</usr/bin/perl> and
180 B</usr/local/bin/perl> to be symlinks to the actual binary. If that
181 can't be done, system administrators are strongly encouraged to put
182 (symlinks to) perl and its accompanying utilities, such as perldoc, into
183 a directory typically found along a user's PATH, or in another obvious
184 and convenient place.
186 In this documentation, C<#!/usr/bin/perl> on the first line of the script
187 will stand in for whatever method works on your system.
191 A single-character switch may be combined with the following switch, if
194 #!/usr/bin/perl -spi.bak # same as -s -p -i.bak
200 =item B<-0>[I<digits>]
202 specifies the input record separator (C<$/>) as an octal number. If there are
203 no digits, the null character is the separator. Other switches may
204 precede or follow the digits. For example, if you have a version of
205 B<find> which can print filenames terminated by the null character, you
208 find . -name '*.bak' -print0 | perl -n0e unlink
210 The special value 00 will cause Perl to slurp files in paragraph mode.
211 The value 0777 will cause Perl to slurp files whole because there is no
212 legal character with that value.
216 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
217 split command to the @F array is done as the first thing inside the
218 implicit while loop produced by the B<-n> or B<-p>.
220 perl -ane 'print pop(@F), "\n";'
229 An alternate delimiter may be specified using B<-F>.
233 causes Perl to check the syntax of the script and then exit without
234 executing it. Actually, it I<will> execute C<BEGIN>, C<END>, and C<use> blocks,
235 because these are considered as occurring outside the execution of
240 runs the script under the Perl debugger. See L<perldebug>.
244 runs the script under the control of a debugging or tracing module
245 installed as Devel::foo. E.g., B<-d:DProf> executes the script using the
246 Devel::DProf profiler. See L<perldebug>.
248 =item B<-D>I<letters>
252 sets debugging flags. To watch how it executes your script, use
253 B<-Dtls>. (This works only if debugging is compiled into your
254 Perl.) Another nice value is B<-Dx>, which lists your compiled
255 syntax tree. And B<-Dr> displays compiled regular expressions. As an
256 alternative, specify a number instead of list of letters (e.g., B<-D14> is
257 equivalent to B<-Dtls>):
259 1 p Tokenizing and parsing
261 4 l Context (loop) stack processing
263 16 o Method and overloading resolution
264 32 c String/numeric conversions
265 64 P Print preprocessor command for -P
266 128 m Memory allocation
267 256 f Format processing
268 512 r Regular expression parsing and execution
269 1024 x Syntax tree dump
270 2048 u Tainting checks
271 4096 L Memory leaks (needs C<-DLEAKTEST> when compiling Perl)
272 8192 H Hash dump -- usurps values()
273 16384 X Scratchpad allocation
276 All these flags require C<-DDEBUGGING> when you compile the Perl
277 executable. This flag is automatically set if you include C<-g>
278 option when C<Configure> asks you about optimizer/debugger flags.
280 =item B<-e> I<commandline>
282 may be used to enter one line of script.
283 If B<-e> is given, Perl
284 will not look for a script filename in the argument list.
285 Multiple B<-e> commands may
286 be given to build up a multi-line script.
287 Make sure to use semicolons where you would in a normal program.
289 =item B<-F>I<pattern>
291 specifies the pattern to split on if B<-a> is also in effect. The
292 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
293 put in single quotes.
297 prints a summary of the options.
299 =item B<-i>[I<extension>]
301 specifies that files processed by the C<E<lt>E<gt>> construct are to be
302 edited in-place. It does this by renaming the input file, opening the
303 output file by the original name, and selecting that output file as the
304 default for print() statements. The extension, if supplied, is used to
305 modify the name of the old file to make a backup copy, following these
308 If no extension is supplied, no backup is made and the current file is
311 If the extension doesn't contain a C<*> then it is appended to the end
312 of the current filename as a suffix.
314 If the extension does contain one or more C<*> characters, then each C<*>
315 is replaced with the current filename. In perl terms you could think of
318 ($backup = $extension) =~ s/\*/$file_name/g;
320 This allows you to add a prefix to the backup file, instead of (or in
321 addition to) a suffix:
323 $ perl -pi'bak_*' -e 's/bar/baz/' fileA # backup to 'bak_fileA'
325 Or even to place backup copies of the original files into another
326 directory (provided the directory already exists):
328 $ perl -pi'old/*.bak' -e 's/bar/baz/' fileA # backup to 'old/fileA.bak'
330 These sets of one-liners are equivalent:
332 $ perl -pi -e 's/bar/baz/' fileA # overwrite current file
333 $ perl -pi'*' -e 's/bar/baz/' fileA # overwrite current file
335 $ perl -pi'.bak' -e 's/bar/baz/' fileA # backup to 'fileA.bak'
336 $ perl -pi'*.bak' -e 's/bar/baz/' fileA # backup to 'fileA.bak'
338 From the shell, saying
340 $ perl -p -i.bak -e "s/foo/bar/; ... "
342 is the same as using the script:
344 #!/usr/bin/perl -pi.bak
347 which is equivalent to
352 if ($ARGV ne $oldargv) {
353 if ($extension !~ /\*/) {
354 $backup = $ARGV . $extension;
357 ($backup = $extension) =~ s/\*/$ARGV/g;
359 rename($ARGV, $backup);
360 open(ARGVOUT, ">$ARGV");
367 print; # this prints to original filename
371 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
372 know when the filename has changed. It does, however, use ARGVOUT for
373 the selected filehandle. Note that STDOUT is restored as the default
374 output filehandle after the loop.
376 As shown above, Perl creates the backup file whether or not any output
377 is actually changed. So this is just a fancy way to copy files:
379 $ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
381 $ perl -p -i'.bak' -e 1 file1 file2 file3...
383 You can use C<eof> without parentheses to locate the end of each input
384 file, in case you want to append to each file, or reset line numbering
385 (see example in L<perlfunc/eof>).
387 If, for a given file, Perl is unable to create the backup file as
388 specified in the extension then it will skip that file and continue on
389 with the next one (if it exists).
391 For a discussion of issues surrounding file permissions and C<-i>, see
392 L<perlfaq5/Why does Perl let me delete read-only files? Why does -i clobber protected files? Isn't this a bug in Perl?>.
394 You cannot use B<-i> to create directories or to strip extensions from
397 Perl does not expand C<~>, so don't do that.
399 Finally, note that the B<-i> switch does not impede execution when no
400 files are given on the command line. In this case, no backup is made
401 (the original file cannot, of course, be determined) and processing
402 proceeds from STDIN to STDOUT as might be expected.
404 =item B<-I>I<directory>
406 Directories specified by B<-I> are prepended to the search path for
407 modules (C<@INC>), and also tells the C preprocessor where to search for
408 include files. The C preprocessor is invoked with B<-P>; by default it
409 searches /usr/include and /usr/lib/perl.
411 =item B<-l>[I<octnum>]
413 enables automatic line-ending processing. It has two effects: first,
414 it automatically chomps "C<$/>" (the input record separator) when used
415 with B<-n> or B<-p>, and second, it assigns "C<$\>"
416 (the output record separator) to have the value of I<octnum> so that
417 any print statements will have that separator added back on. If
418 I<octnum> is omitted, sets "C<$\>" to the current value of "C<$/>". For
419 instance, to trim lines to 80 columns:
421 perl -lpe 'substr($_, 80) = ""'
423 Note that the assignment C<$\ = $/> is done when the switch is processed,
424 so the input record separator can be different than the output record
425 separator if the B<-l> switch is followed by a B<-0> switch:
427 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
429 This sets C<$\> to newline and then sets C<$/> to the null character.
431 =item B<-m>[B<->]I<module>
433 =item B<-M>[B<->]I<module>
435 =item B<-M>[B<->]I<'module ...'>
437 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
439 C<-m>I<module> executes C<use> I<module> C<();> before executing your
442 C<-M>I<module> executes C<use> I<module> C<;> before executing your
443 script. You can use quotes to add extra code after the module name,
444 e.g., C<-M'module qw(foo bar)'>.
446 If the first character after the C<-M> or C<-m> is a dash (C<->)
447 then the 'use' is replaced with 'no'.
449 A little builtin syntactic sugar means you can also say
450 C<-mmodule=foo,bar> or C<-Mmodule=foo,bar> as a shortcut for
451 C<-M'module qw(foo bar)'>. This avoids the need to use quotes when
452 importing symbols. The actual code generated by C<-Mmodule=foo,bar> is
453 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
454 removes the distinction between C<-m> and C<-M>.
458 causes Perl to assume the following loop around your script, which
459 makes it iterate over filename arguments somewhat like B<sed -n> or
463 ... # your script goes here
466 Note that the lines are not printed by default. See B<-p> to have
467 lines printed. If a file named by an argument cannot be opened for
468 some reason, Perl warns you about it, and moves on to the next file.
470 Here is an efficient way to delete all files older than a week:
472 find . -mtime +7 -print | perl -nle 'unlink;'
474 This is faster than using the C<-exec> switch of B<find> because you don't
475 have to start a process on every filename found.
477 C<BEGIN> and C<END> blocks may be used to capture control before or after
478 the implicit loop, just as in B<awk>.
482 causes Perl to assume the following loop around your script, which
483 makes it iterate over filename arguments somewhat like B<sed>:
487 ... # your script goes here
489 print or die "-p destination: $!\n";
492 If a file named by an argument cannot be opened for some reason, Perl
493 warns you about it, and moves on to the next file. Note that the
494 lines are printed automatically. An error occuring during printing is
495 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
496 overrides a B<-n> switch.
498 C<BEGIN> and C<END> blocks may be used to capture control before or after
499 the implicit loop, just as in awk.
503 causes your script to be run through the C preprocessor before
504 compilation by Perl. (Because both comments and cpp directives begin
505 with the # character, you should avoid starting comments with any words
506 recognized by the C preprocessor such as "if", "else", or "define".)
510 enables some rudimentary switch parsing for switches on the command
511 line after the script name but before any filename arguments (or before
512 a B<-->). Any switch found there is removed from @ARGV and sets the
513 corresponding variable in the Perl script. The following script
514 prints "true" if and only if the script is invoked with a B<-xyz> switch.
517 if ($xyz) { print "true\n"; }
521 makes Perl use the PATH environment variable to search for the
522 script (unless the name of the script contains directory separators).
523 On some platforms, this also makes Perl append suffixes to the
524 filename while searching for it. For example, on Win32 platforms,
525 the ".bat" and ".cmd" suffixes are appended if a lookup for the
526 original name fails, and if the name does not already end in one
527 of those suffixes. If your Perl was compiled with DEBUGGING turned
528 on, using the -Dp switch to Perl shows how the search progresses.
530 If the filename supplied contains directory separators (i.e. it is an
531 absolute or relative pathname), and if the file is not found,
532 platforms that append file extensions will do so and try to look
533 for the file with those extensions added, one by one.
535 On DOS-like platforms, if the script does not contain directory
536 separators, it will first be searched for in the current directory
537 before being searched for on the PATH. On Unix platforms, the
538 script will be searched for strictly on the PATH.
540 Typically this is used to emulate #! startup on platforms that
541 don't support #!. This example works on many platforms that
542 have a shell compatible with Bourne shell:
545 eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
546 if $running_under_some_shell;
548 The system ignores the first line and feeds the script to /bin/sh,
549 which proceeds to try to execute the Perl script as a shell script.
550 The shell executes the second line as a normal shell command, and thus
551 starts up the Perl interpreter. On some systems $0 doesn't always
552 contain the full pathname, so the B<-S> tells Perl to search for the
553 script if necessary. After Perl locates the script, it parses the
554 lines and ignores them because the variable $running_under_some_shell
555 is never true. If the script will be interpreted by csh, you will need
556 to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
557 embedded spaces (and such) in the argument list. To start up sh rather
558 than csh, some systems may have to replace the #! line with a line
559 containing just a colon, which will be politely ignored by Perl. Other
560 systems can't control that, and need a totally devious construct that
561 will work under any of csh, sh, or Perl, such as the following:
563 eval '(exit $?0)' && eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
564 & eval 'exec /usr/bin/perl -wS $0 $argv:q'
565 if $running_under_some_shell;
569 forces "taint" checks to be turned on so you can test them. Ordinarily
570 these checks are done only when running setuid or setgid. It's a good
571 idea to turn them on explicitly for programs run on another's behalf,
572 such as CGI programs. See L<perlsec>. Note that (for security reasons)
573 this option must be seen by Perl quite early; usually this means it must
574 appear early on the command line or in the #! line (for systems which
579 causes Perl to dump core after compiling your script. You can then
580 in theory take this core dump and turn it into an executable file by using the
581 B<undump> program (not supplied). This speeds startup at the expense of
582 some disk space (which you can minimize by stripping the executable).
583 (Still, a "hello world" executable comes out to about 200K on my
584 machine.) If you want to execute a portion of your script before dumping,
585 use the dump() operator instead. Note: availability of B<undump> is
586 platform specific and may not be available for a specific port of
587 Perl. It has been superseded by the new perl-to-C compiler, which is more
588 portable, even though it's still only considered beta.
592 allows Perl to do unsafe operations. Currently the only "unsafe"
593 operations are the unlinking of directories while running as superuser,
594 and running setuid programs with fatal taint checks turned into
595 warnings. Note that the B<-w> switch (or the C<$^W> variable) must
596 be used along with this option to actually B<generate> the
597 taint-check warnings.
601 prints the version and patchlevel of your Perl executable.
605 prints summary of the major perl configuration values and the current
610 Prints to STDOUT the value of the named configuration variable.
614 prints warnings about variable names that are mentioned only once, and
615 scalar variables that are used before being set. Also warns about
616 redefined subroutines, and references to undefined filehandles or
617 filehandles opened read-only that you are attempting to write on. Also
618 warns you if you use values as a number that doesn't look like numbers,
619 using an array as though it were a scalar, if your subroutines recurse
620 more than 100 deep, and innumerable other things.
622 You can disable specific warnings using C<__WARN__> hooks, as described
623 in L<perlvar> and L<perlfunc/warn>. See also L<perldiag> and L<perltrap>.
625 =item B<-x> I<directory>
627 tells Perl that the script is embedded in a message. Leading
628 garbage will be discarded until the first line that starts with #! and
629 contains the string "perl". Any meaningful switches on that line will
630 be applied. If a directory name is specified, Perl will switch to
631 that directory before running the script. The B<-x> switch controls
632 only the disposal of leading garbage. The script must be
633 terminated with C<__END__> if there is trailing garbage to be ignored (the
634 script can process any or all of the trailing garbage via the DATA
635 filehandle if desired).
645 Used if chdir has no argument.
649 Used if chdir has no argument and HOME is not set.
653 Used in executing subprocesses, and in finding the script if B<-S> is
658 A colon-separated list of directories in which to look for Perl library
659 files before looking in the standard library and the current
660 directory. If PERL5LIB is not defined, PERLLIB is used. When running
661 taint checks (because the script was running setuid or setgid, or the
662 B<-T> switch was used), neither variable is used. The script should
665 use lib "/my/directory";
669 Command-line options (switches). Switches in this variable are taken
670 as if they were on every Perl command line. Only the B<-[DIMUdmw]>
671 switches are allowed. When running taint checks (because the script
672 was running setuid or setgid, or the B<-T> switch was used), this
677 A colon-separated list of directories in which to look for Perl library
678 files before looking in the standard library and the current directory.
679 If PERL5LIB is defined, PERLLIB is not used.
683 The command used to load the debugger code. The default is:
685 BEGIN { require 'perl5db.pl' }
687 =item PERL5SHELL (specific to WIN32 port)
689 May be set to an alternative shell that perl must use internally for
690 executing "backtick" commands or system(). Default is C<cmd.exe /x/c>
691 on WindowsNT and C<command.com /c> on Windows95. The value is considered
692 to be space delimited. Precede any character that needs to be protected
693 (like a space or backslash) with a backslash.
695 Note that Perl doesn't use COMSPEC for this purpose because
696 COMSPEC has a high degree of variability among users, leading to
697 portability concerns. Besides, perl can use a shell that may not be
698 fit for interactive use, and setting COMSPEC to such a shell may
699 interfere with the proper functioning of other programs (which usually
700 look in COMSPEC to find a shell fit for interactive use).
702 =item PERL_DEBUG_MSTATS
704 Relevant only if perl is compiled with the malloc included with the perl
705 distribution (that is, if C<perl -V:d_mymalloc> is 'define').
706 If set, this causes memory statistics to be dumped after execution. If set
707 to an integer greater than one, also causes memory statistics to be dumped
710 =item PERL_DESTRUCT_LEVEL
712 Relevant only if your perl executable was built with B<-DDEBUGGING>,
713 this controls the behavior of global destruction of objects and other
718 Perl also has environment variables that control how Perl handles data
719 specific to particular natural languages. See L<perllocale>.
721 Apart from these, Perl uses no other environment variables, except
722 to make them available to the script being executed, and to child
723 processes. However, scripts running setuid would do well to execute
724 the following lines before doing anything else, just to keep people
727 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
728 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
729 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};