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 way.)
36 Passed in implicitly via standard input. This works only if there are
37 no filename arguments--to pass arguments to a STDIN script you
38 must explicitly specify a "-" for the script name.
42 With methods 2 and 3, Perl starts parsing the input file from the
43 beginning, unless you've specified a B<-x> switch, in which case it
44 scans for the first line starting with #! and containing the word
45 "perl", and starts there instead. This is useful for running a script
46 embedded in a larger message. (In this case you would indicate the end
47 of the script using the C<__END__> token.)
49 The #! line is always examined for switches as the line is being
50 parsed. Thus, if you're on a machine that allows only one argument
51 with the #! line, or worse, doesn't even recognize the #! line, you
52 still can get consistent switch behavior regardless of how Perl was
53 invoked, even if B<-x> was used to find the beginning of the script.
55 Because many operating systems silently chop off kernel interpretation of
56 the #! line after 32 characters, some switches may be passed in on the
57 command line, and some may not; you could even get a "-" without its
58 letter, if you're not careful. You probably want to make sure that all
59 your switches fall either before or after that 32 character boundary.
60 Most switches don't actually care if they're processed redundantly, but
61 getting a - instead of a complete switch could cause Perl to try to
62 execute standard input instead of your script. And a partial B<-I> switch
63 could also cause odd results.
65 Parsing of the #! switches starts wherever "perl" is mentioned in the line.
66 The sequences "-*" and "- " are specifically ignored so that you could,
67 if you were so inclined, say
69 #!/bin/sh -- # -*- perl -*- -p
70 eval 'exec /usr/bin/perl $0 -S ${1+"$@"}'
71 if $running_under_some_shell;
73 to let Perl see the B<-p> switch.
75 If the #! line does not contain the word "perl", the program named after
76 the #! is executed instead of the Perl interpreter. This is slightly
77 bizarre, but it helps people on machines that don't do #!, because they
78 can tell a program that their SHELL is /usr/bin/perl, and Perl will then
79 dispatch the program to the correct interpreter for them.
81 After locating your script, Perl compiles the entire script to an
82 internal form. If there are any compilation errors, execution of the
83 script is not attempted. (This is unlike the typical shell script,
84 which might run part-way through before finding a syntax error.)
86 If the script is syntactically correct, it is executed. If the script
87 runs off the end without hitting an exit() or die() operator, an implicit
88 C<exit(0)> is provided to indicate successful completion.
90 =head2 #! and quoting on non-Unix systems
92 Unix's #! technique can be simulated on other systems:
100 extproc perl -S -your_switches
102 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
107 Create a batch file to run your script, and codify it in
108 C<ALTERNATIVE_SHEBANG> (see the F<dosish.h> file in the source
109 distribution for more information).
113 The Win95/NT installation, when using the Activeware port of Perl,
114 will modify the Registry to associate the .pl extension with the perl
115 interpreter. If you install another port of Perl, including the one
116 in the Win32 directory of the Perl distribution, then you'll have to
117 modify the Registry yourself.
121 Macintosh perl scripts will have the appropriate Creator and
122 Type, so that double-clicking them will invoke the perl application.
126 Command-interpreters on non-Unix systems have rather different ideas
127 on quoting than Unix shells. You'll need to learn the special
128 characters in your command-interpreter (C<*>, C<\> and C<"> are
129 common) and how to protect whitespace and these characters to run
130 one-liners (see C<-e> below).
132 On some systems, you may have to change single-quotes to double ones,
133 which you must I<NOT> do on Unix or Plan9 systems. You might also
134 have to change a single % to a %%.
139 perl -e 'print "Hello world\n"'
142 perl -e "print \"Hello world\n\""
145 print "Hello world\n"
146 (then Run "Myscript" or Shift-Command-R)
149 perl -e "print ""Hello world\n"""
151 The problem is that none of this is reliable: it depends on the command
152 and it is entirely possible neither works. If 4DOS was the command shell, this would
153 probably work better:
155 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
157 CMD.EXE in Windows NT slipped a lot of standard Unix functionality in
158 when nobody was looking, but just try to find documentation for its
161 Under the Macintosh, it depends which environment you are using. The MacPerl
162 shell, or MPW, is much like Unix shells in its support for several
163 quoting variants, except that it makes free use of the Macintosh's non-ASCII
164 characters as control characters.
166 There is no general solution to all of this. It's just a mess.
170 A single-character switch may be combined with the following switch, if
173 #!/usr/bin/perl -spi.bak # same as -s -p -i.bak
179 =item B<-0>[I<digits>]
181 specifies the input record separator (C<$/>) as an octal number. If there are
182 no digits, the null character is the separator. Other switches may
183 precede or follow the digits. For example, if you have a version of
184 B<find> which can print filenames terminated by the null character, you
187 find . -name '*.bak' -print0 | perl -n0e unlink
189 The special value 00 will cause Perl to slurp files in paragraph mode.
190 The value 0777 will cause Perl to slurp files whole because there is no
191 legal character with that value.
195 turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
196 split command to the @F array is done as the first thing inside the
197 implicit while loop produced by the B<-n> or B<-p>.
199 perl -ane 'print pop(@F), "\n";'
208 An alternate delimiter may be specified using B<-F>.
212 causes Perl to check the syntax of the script and then exit without
213 executing it. Actually, it I<will> execute C<BEGIN>, C<END>, and C<use> blocks,
214 because these are considered as occurring outside the execution of
219 runs the script under the Perl debugger. See L<perldebug>.
223 runs the script under the control of a debugging or tracing module
224 installed as Devel::foo. E.g., B<-d:DProf> executes the script using the
225 Devel::DProf profiler. See L<perldebug>.
231 sets debugging flags. To watch how it executes your script, use
232 B<-D14>. (This works only if debugging is compiled into your
233 Perl.) Another nice value is B<-D1024>, which lists your compiled
234 syntax tree. And B<-D512> displays compiled regular expressions. As an
235 alternative specify a list of letters instead of numbers (e.g., B<-D14> is
236 equivalent to B<-Dtls>):
238 1 p Tokenizing and Parsing
240 4 l Label Stack Processing
242 16 o Operator Node Construction
243 32 c String/Numeric Conversions
244 64 P Print Preprocessor Command for -P
245 128 m Memory Allocation
246 256 f Format Processing
247 512 r Regular Expression Parsing
248 1024 x Syntax Tree Dump
249 2048 u Tainting Checks
250 4096 L Memory Leaks (not supported anymore)
251 8192 H Hash Dump -- usurps values()
252 16384 X Scratchpad Allocation
255 =item B<-e> I<commandline>
257 may be used to enter one line of script.
258 If B<-e> is given, Perl
259 will not look for a script filename in the argument list.
260 Multiple B<-e> commands may
261 be given to build up a multi-line script.
262 Make sure to use semicolons where you would in a normal program.
264 =item B<-F>I<pattern>
266 specifies the pattern to split on if B<-a> is also in effect. The
267 pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
268 put in single quotes.
272 prints a summary of the options.
274 =item B<-i>[I<extension>]
276 specifies that files processed by the C<E<lt>E<gt>> construct are to be edited
277 in-place. It does this by renaming the input file, opening the output
278 file by the original name, and selecting that output file as the default
279 for print() statements. The extension, if supplied, is added to the name
280 of the old file to make a backup copy. If no extension is supplied, no
281 backup is made. From the shell, saying
283 $ perl -p -i.bak -e "s/foo/bar/; ... "
285 is the same as using the script:
287 #!/usr/bin/perl -pi.bak
290 which is equivalent to
294 if ($ARGV ne $oldargv) {
295 rename($ARGV, $ARGV . '.bak');
296 open(ARGVOUT, ">$ARGV");
303 print; # this prints to original filename
307 except that the B<-i> form doesn't need to compare $ARGV to $oldargv to
308 know when the filename has changed. It does, however, use ARGVOUT for
309 the selected filehandle. Note that STDOUT is restored as the
310 default output filehandle after the loop.
312 You can use C<eof> without parenthesis to locate the end of each input file,
313 in case you want to append to each file, or reset line numbering (see
314 example in L<perlfunc/eof>).
316 =item B<-I>I<directory>
318 Directories specified by B<-I> are prepended to the search path for
319 modules (C<@INC>), and also tells the C preprocessor where to search for
320 include files. The C preprocessor is invoked with B<-P>; by default it
321 searches /usr/include and /usr/lib/perl.
323 =item B<-l>[I<octnum>]
325 enables automatic line-ending processing. It has two effects: first,
326 it automatically chomps "C<$/>" (the input record separator) when used
327 with B<-n> or B<-p>, and second, it assigns "C<$\>"
328 (the output record separator) to have the value of I<octnum> so that
329 any print statements will have that separator added back on. If
330 I<octnum> is omitted, sets "C<$\>" to the current value of "C<$/>". For
331 instance, to trim lines to 80 columns:
333 perl -lpe 'substr($_, 80) = ""'
335 Note that the assignment C<$\ = $/> is done when the switch is processed,
336 so the input record separator can be different than the output record
337 separator if the B<-l> switch is followed by a B<-0> switch:
339 gnufind / -print0 | perl -ln0e 'print "found $_" if -p'
341 This sets C<$\> to newline and then sets C<$/> to the null character.
343 =item B<-m>[B<->]I<module>
345 =item B<-M>[B<->]I<module>
347 =item B<-M>[B<->]I<'module ...'>
349 =item B<-[mM]>[B<->]I<module=arg[,arg]...>
351 C<-m>I<module> executes C<use> I<module> C<();> before executing your
354 C<-M>I<module> executes C<use> I<module> C<;> before executing your
355 script. You can use quotes to add extra code after the module name,
356 e.g., C<-M'module qw(foo bar)'>.
358 If the first character after the C<-M> or C<-m> is a dash (C<->)
359 then the 'use' is replaced with 'no'.
361 A little builtin syntactic sugar means you can also say
362 C<-mmodule=foo,bar> or C<-Mmodule=foo,bar> as a shortcut for
363 C<-M'module qw(foo bar)'>. This avoids the need to use quotes when
364 importing symbols. The actual code generated by C<-Mmodule=foo,bar> is
365 C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
366 removes the distinction between C<-m> and C<-M>.
370 causes Perl to assume the following loop around your script, which
371 makes it iterate over filename arguments somewhat like B<sed -n> or
375 ... # your script goes here
378 Note that the lines are not printed by default. See B<-p> to have
379 lines printed. If a file named by an argument cannot be opened for
380 some reason, Perl warns you about it, and moves on to the next file.
382 Here is an efficient way to delete all files older than a week:
384 find . -mtime +7 -print | perl -nle 'unlink;'
386 This is faster than using the C<-exec> switch of B<find> because you don't
387 have to start a process on every filename found.
389 C<BEGIN> and C<END> blocks may be used to capture control before or after
390 the implicit loop, just as in B<awk>.
394 causes Perl to assume the following loop around your script, which
395 makes it iterate over filename arguments somewhat like B<sed>:
399 ... # your script goes here
401 print or die "-p destination: $!\n";
404 If a file named by an argument cannot be opened for some reason, Perl
405 warns you about it, and moves on to the next file. Note that the
406 lines are printed automatically. An error occuring during printing is
407 treated as fatal. To suppress printing use the B<-n> switch. A B<-p>
408 overrides a B<-n> switch.
410 C<BEGIN> and C<END> blocks may be used to capture control before or after
411 the implicit loop, just as in awk.
415 causes your script to be run through the C preprocessor before
416 compilation by Perl. (Because both comments and cpp directives begin
417 with the # character, you should avoid starting comments with any words
418 recognized by the C preprocessor such as "if", "else", or "define".)
422 enables some rudimentary switch parsing for switches on the command
423 line after the script name but before any filename arguments (or before
424 a B<-->). Any switch found there is removed from @ARGV and sets the
425 corresponding variable in the Perl script. The following script
426 prints "true" if and only if the script is invoked with a B<-xyz> switch.
429 if ($xyz) { print "true\n"; }
433 makes Perl use the PATH environment variable to search for the
434 script (unless the name of the script starts with a slash). Typically
435 this is used to emulate #! startup on machines that don't support #!,
436 in the following manner:
439 eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
440 if $running_under_some_shell;
442 The system ignores the first line and feeds the script to /bin/sh,
443 which proceeds to try to execute the Perl script as a shell script.
444 The shell executes the second line as a normal shell command, and thus
445 starts up the Perl interpreter. On some systems $0 doesn't always
446 contain the full pathname, so the B<-S> tells Perl to search for the
447 script if necessary. After Perl locates the script, it parses the
448 lines and ignores them because the variable $running_under_some_shell
449 is never true. A better construct than C<$*> would be C<${1+"$@"}>, which
450 handles embedded spaces and such in the filenames, but doesn't work if
451 the script is being interpreted by csh. To start up sh rather
452 than csh, some systems may have to replace the #! line with a line
453 containing just a colon, which will be politely ignored by Perl. Other
454 systems can't control that, and need a totally devious construct that
455 will work under any of csh, sh, or Perl, such as the following:
457 eval '(exit $?0)' && eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
458 & eval 'exec /usr/bin/perl -S $0 $argv:q'
459 if $running_under_some_shell;
463 forces "taint" checks to be turned on so you can test them. Ordinarily these checks are
464 done only when running setuid or setgid. It's a good idea to turn
465 them on explicitly for programs run on another's behalf, such as CGI
466 programs. See L<perlsec>.
470 causes Perl to dump core after compiling your script. You can then
471 take this core dump and turn it into an executable file by using the
472 B<undump> program (not supplied). This speeds startup at the expense of
473 some disk space (which you can minimize by stripping the executable).
474 (Still, a "hello world" executable comes out to about 200K on my
475 machine.) If you want to execute a portion of your script before dumping,
476 use the dump() operator instead. Note: availability of B<undump> is
477 platform specific and may not be available for a specific port of
482 allows Perl to do unsafe operations. Currently the only "unsafe"
483 operations are the unlinking of directories while running as superuser,
484 and running setuid programs with fatal taint checks turned into
489 prints the version and patchlevel of your Perl executable.
493 prints summary of the major perl configuration values and the current
498 Prints to STDOUT the value of the named configuration variable.
502 prints warnings about variable names that are mentioned only once, and
503 scalar variables that are used before being set. Also warns about
504 redefined subroutines, and references to undefined filehandles or
505 filehandles opened read-only that you are attempting to write on. Also
506 warns you if you use values as a number that doesn't look like numbers,
507 using an array as though it were a scalar, if your subroutines recurse
508 more than 100 deep, and innumerable other things.
510 You can disable specific warnings using C<__WARN__> hooks, as described
511 in L<perlvar> and L<perlfunc/warn>. See also L<perldiag> and L<perltrap>.
513 =item B<-x> I<directory>
515 tells Perl that the script is embedded in a message. Leading
516 garbage will be discarded until the first line that starts with #! and
517 contains the string "perl". Any meaningful switches on that line will
518 be applied. If a directory name is specified, Perl will switch to
519 that directory before running the script. The B<-x> switch controls
520 only the disposal of leading garbage. The script must be
521 terminated with C<__END__> if there is trailing garbage to be ignored (the
522 script can process any or all of the trailing garbage via the DATA
523 filehandle if desired).
533 Used if chdir has no argument.
537 Used if chdir has no argument and HOME is not set.
541 Used in executing subprocesses, and in finding the script if B<-S> is
546 A colon-separated list of directories in which to look for Perl library
547 files before looking in the standard library and the current
548 directory. If PERL5LIB is not defined, PERLLIB is used. When running
549 taint checks (because the script was running setuid or setgid, or the
550 B<-T> switch was used), neither variable is used. The script should
553 use lib "/my/directory";
557 Command-line options (switches). Switches in this variable are taken
558 as if they were on every Perl command line. Only the B<-[DIMUdmw]>
559 switches are allowed. When running taint checks (because the script
560 was running setuid or setgid, or the B<-T> switch was used), this
565 A colon-separated list of directories in which to look for Perl library
566 files before looking in the standard library and the current directory.
567 If PERL5LIB is defined, PERLLIB is not used.
571 The command used to load the debugger code. The default is:
573 BEGIN { require 'perl5db.pl' }
575 =item PERL5SHELL (specific to WIN32 port)
577 May be set to an alternative shell that perl must use internally for
578 executing "backtick" commands or system(). Perl doesn't use COMSPEC
579 for this purpose because COMSPEC has a high degree of variability
580 among users, leading to portability concerns. Besides, perl can use
581 a shell that may not be fit for interactive use, and setting COMSPEC
582 to such a shell may interfere with the proper functioning of other
583 programs (which usually look in COMSPEC to find a shell fit for
586 =item PERL_DEBUG_MSTATS
588 Relevant only if your perl executable was built with B<-DDEBUGGING_MSTATS>,
589 if set, this causes memory statistics to be dumped after execution. If set
590 to an integer greater than one, also causes memory statistics to be dumped
593 =item PERL_DESTRUCT_LEVEL
595 Relevant only if your perl executable was built with B<-DDEBUGGING>,
596 this controls the behavior of global destruction of objects and other
601 Perl also has environment variables that control how Perl handles data
602 specific to particular natural languages. See L<perllocale>.
604 Apart from these, Perl uses no other environment variables, except
605 to make them available to the script being executed, and to child
606 processes. However, scripts running setuid would do well to execute
607 the following lines before doing anything else, just to keep people
610 $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
611 $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
612 delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};