3 perlfaq3 - Programming Tools ($Revision: 7875 $)
7 This section of the FAQ answers questions related to programmer tools
8 and programming support.
10 =head2 How do I do (anything)?
12 Have you looked at CPAN (see L<perlfaq2>)? The chances are that
13 someone has already written a module that can solve your problem.
14 Have you read the appropriate manpages? Here's a brief index:
16 Basics perldata, perlvar, perlsyn, perlop, perlsub
17 Execution perlrun, perldebug
19 Objects perlref, perlmod, perlobj, perltie
20 Data Structures perlref, perllol, perldsc
21 Modules perlmod, perlmodlib, perlsub
22 Regexes perlre, perlfunc, perlop, perllocale
23 Moving to perl5 perltrap, perl
24 Linking w/C perlxstut, perlxs, perlcall, perlguts, perlembed
25 Various http://www.cpan.org/misc/olddoc/FMTEYEWTK.tgz
26 (not a man-page but still useful, a collection
27 of various essays on Perl techniques)
29 A crude table of contents for the Perl manpage set is found in L<perltoc>.
31 =head2 How can I use Perl interactively?
33 The typical approach uses the Perl debugger, described in the
34 perldebug(1) manpage, on an "empty" program, like this:
38 Now just type in any legal Perl code, and it will be immediately
39 evaluated. You can also examine the symbol table, get stack
40 backtraces, check variable values, set breakpoints, and other
41 operations typically found in symbolic debuggers.
43 =head2 Is there a Perl shell?
45 The psh (Perl sh) is currently at version 1.8. The Perl Shell is a shell
46 that combines the interactive nature of a Unix shell with the power of
47 Perl. The goal is a full featured shell that behaves as expected for
48 normal shell activity and uses Perl syntax and functionality for
49 control-flow statements and other things. You can get psh at
50 http://sourceforge.net/projects/psh/ .
52 Zoidberg is a similar project and provides a shell written in perl,
53 configured in perl and operated in perl. It is intended as a login shell
54 and development environment. It can be found at http://zoidberg.sf.net/
55 or your local CPAN mirror.
57 The Shell.pm module (distributed with Perl) makes Perl try commands
58 which aren't part of the Perl language as shell commands. perlsh from
59 the source distribution is simplistic and uninteresting, but may still
62 =head2 How do I find which modules are installed on my system?
64 You can use the ExtUtils::Installed module to show all installed
65 distributions, although it can take awhile to do its magic. The
66 standard library which comes with Perl just shows up as "Perl" (although
67 you can get those with Module::CoreList).
69 use ExtUtils::Installed;
71 my $inst = ExtUtils::Installed->new();
72 my @modules = $inst->modules();
74 If you want a list of all of the Perl module filenames, you
75 can use File::Find::Rule.
79 my @files = File::Find::Rule->file()->name( '*.pm' )->in( @INC );
81 If you do not have that module, you can do the same thing
82 with File::Find which is part of the standard library.
89 push @files, $File::Find::name
90 if -f $File::Find::name && /\.pm$/
96 print join "\n", @files;
98 If you simply need to quickly check to see if a module is
99 available, you can check for its documentation. If you can
100 read the documentation the module is most likely installed.
101 If you cannot read the documentation, the module might not
102 have any (in rare cases).
104 prompt% perldoc Module::Name
106 You can also try to include the module in a one-liner to see if
109 perl -MModule::Name -e1
111 =head2 How do I debug my Perl programs?
113 (contributed by brian d foy)
115 Before you do anything else, you can help yourself by ensuring that
116 you let Perl tell you about problem areas in your code. By turning
117 on warnings and strictures, you can head off many problems before
118 they get too big. You can find out more about these in L<strict>
125 Beyond that, the simplest debugger is the C<print> function. Use it
126 to look at values as you run your program:
128 print STDERR "The value is [$value]\n";
130 The C<Data::Dumper> module can pretty-print Perl data structures:
132 use Data::Dumper qw( Dumper );
133 print STDERR "The hash is " . Dumper( \%hash ) . "\n";
135 Perl comes with an interactive debugger, which you can start with the
136 C<-d> switch. It's fully explained in L<perldebug>.
138 If you'd like a graphical user interface and you have Tk, you can use
139 C<ptkdb>. It's on CPAN and available for free.
141 If you need something much more sophisicated and controllable, Leon
142 Brocard's Devel::ebug (which you can call with the -D switch as -Debug)
143 gives you the programmatic hooks into everything you need to write your
144 own (without too much pain and suffering).
146 You can also use a commercial debugger such as Affrus (Mac OS X), Komodo
147 from Activestate (Windows and Mac OS X), or EPIC (most platforms).
149 =head2 How do I profile my Perl programs?
151 You should get the Devel::DProf module from the standard distribution
152 (or separately on CPAN) and also use Benchmark.pm from the standard
153 distribution. The Benchmark module lets you time specific portions of
154 your code, while Devel::DProf gives detailed breakdowns of where your
155 code spends its time.
157 Here's a sample use of Benchmark:
161 @junk = `cat /etc/motd`;
165 'map' => sub { my @a = @junk;
168 'for' => sub { my @a = @junk;
173 This is what it prints (on one machine--your results will be dependent
174 on your hardware, operating system, and the load on your machine):
176 Benchmark: timing 10000 iterations of for, map...
177 for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu)
178 map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu)
180 Be aware that a good benchmark is very hard to write. It only tests the
181 data you give it and proves little about the differing complexities
182 of contrasting algorithms.
184 =head2 How do I cross-reference my Perl programs?
186 The B::Xref module can be used to generate cross-reference reports
189 perl -MO=Xref[,OPTIONS] scriptname.plx
191 =head2 Is there a pretty-printer (formatter) for Perl?
193 Perltidy is a Perl script which indents and reformats Perl scripts
194 to make them easier to read by trying to follow the rules of the
195 L<perlstyle>. If you write Perl scripts, or spend much time reading
196 them, you will probably find it useful. It is available at
197 http://perltidy.sourceforge.net
199 Of course, if you simply follow the guidelines in L<perlstyle>,
200 you shouldn't need to reformat. The habit of formatting your code
201 as you write it will help prevent bugs. Your editor can and should
202 help you with this. The perl-mode or newer cperl-mode for emacs
203 can provide remarkable amounts of help with most (but not all)
204 code, and even less programmable editors can provide significant
205 assistance. Tom Christiansen and many other VI users swear by
206 the following settings in vi and its clones:
211 Put that in your F<.exrc> file (replacing the caret characters
212 with control characters) and away you go. In insert mode, ^T is
213 for indenting, ^D is for undenting, and ^O is for blockdenting--as
214 it were. A more complete example, with comments, can be found at
215 http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz
217 The a2ps http://www-inf.enst.fr/%7Edemaille/a2ps/black+white.ps.gz does
218 lots of things related to generating nicely printed output of
219 documents, as does enscript at http://people.ssh.fi/mtr/genscript/ .
221 =head2 Is there a ctags for Perl?
223 (contributed by brian d foy)
225 Ctags uses an index to quickly find things in source code, and many
226 popular editors support ctags for several different languages,
229 Exuberent ctags supports Perl: http://ctags.sourceforge.net/
231 You might also try pltags: http://www.mscha.com/pltags.zip
233 =head2 Is there an IDE or Windows Perl Editor?
235 Perl programs are just plain text, so any editor will do.
237 If you're on Unix, you already have an IDE--Unix itself. The UNIX
238 philosophy is the philosophy of several small tools that each do one
239 thing and do it well. It's like a carpenter's toolbox.
241 If you want an IDE, check the following (in alphabetical order, not
242 order of preference):
248 http://e-p-i-c.sf.net/
250 The Eclipse Perl Integration Project integrates Perl
251 editing/debugging with Eclipse.
255 http://www.enginsite.com/
257 Perl Editor by EngInSite is a complete integrated development
258 environment (IDE) for creating, testing, and debugging Perl scripts;
259 the tool runs on Windows 9x/NT/2000/XP or later.
263 http://www.ActiveState.com/Products/Komodo/
265 ActiveState's cross-platform (as of October 2004, that's Windows, Linux,
266 and Solaris), multi-language IDE has Perl support, including a regular expression
267 debugger and remote debugging.
271 http://open-perl-ide.sourceforge.net/
273 Open Perl IDE is an integrated development environment for writing
274 and debugging Perl scripts with ActiveState's ActivePerl distribution
275 under Windows 95/98/NT/2000.
279 http://www.optiperl.com/
281 OptiPerl is a Windows IDE with simulated CGI environment, including
282 debugger and syntax highlighting editor.
286 http://www.solutionsoft.com/perl.htm
288 PerlBuidler is an integrated development environment for Windows that
289 supports Perl development.
293 http://helpconsulting.net/visiperl/
295 From Help Consulting, for Windows.
299 http://www.activestate.com/Products/Visual_Perl/
301 Visual Perl is a Visual Studio.NET plug-in from ActiveState.
305 http://www.zeusedit.com/lookmain.html
307 Zeus for Window is another Win32 multi-language editor/IDE
308 that comes with support for Perl:
312 For editors: if you're on Unix you probably have vi or a vi clone
313 already, and possibly an emacs too, so you may not need to download
314 anything. In any emacs the cperl-mode (M-x cperl-mode) gives you
315 perhaps the best available Perl editing mode in any editor.
317 If you are using Windows, you can use any editor that lets you work
318 with plain text, such as NotePad or WordPad. Word processors, such as
319 Microsoft Word or WordPerfect, typically do not work since they insert
320 all sorts of behind-the-scenes information, although some allow you to
321 save files as "Text Only". You can also download text editors designed
322 specifically for programming, such as Textpad (
323 http://www.textpad.com/ ) and UltraEdit ( http://www.ultraedit.com/ ),
326 If you are using MacOS, the same concerns apply. MacPerl (for Classic
327 environments) comes with a simple editor. Popular external editors are
328 BBEdit ( http://www.bbedit.com/ ) or Alpha (
329 http://www.his.com/~jguyer/Alpha/Alpha8.html ). MacOS X users can use
330 Unix editors as well. Neil Bowers (the man behind Geekcruises) has a
331 list of Mac editors that can handle Perl (
332 http://www.neilbowers.org/macperleditors.html ).
338 http://www.gnu.org/software/emacs/windows/ntemacs.html
342 http://www.microemacs.de/
346 http://www.xemacs.org/Download/index.html
350 http://space.mit.edu/~davis/jed/
354 or a vi clone such as
360 ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/
364 http://dickey.his.com/vile/vile.html
372 For vi lovers in general, Windows or elsewhere:
374 http://www.thomer.com/thomer/vi/vi.html
376 nvi ( http://www.bostic.com/vi/ , available from CPAN in src/misc/) is
377 yet another vi clone, unfortunately not available for Windows, but in
378 UNIX platforms you might be interested in trying it out, firstly because
379 strictly speaking it is not a vi clone, it is the real vi, or the new
380 incarnation of it, and secondly because you can embed Perl inside it
381 to use Perl as the scripting language. nvi is not alone in this,
382 though: at least also vim and vile offer an embedded Perl.
384 The following are Win32 multilanguage editor/IDESs that support Perl:
390 http://www.borland.com/codewright/
394 http://www.MultiEdit.com/
398 http://www.slickedit.com/
402 There is also a toyedit Text widget based editor written in Perl
403 that is distributed with the Tk module on CPAN. The ptkdb
404 ( http://world.std.com/~aep/ptkdb/ ) is a Perl/tk based debugger that
405 acts as a development environment of sorts. Perl Composer
406 ( http://perlcomposer.sourceforge.net/ ) is an IDE for Perl/Tk
409 In addition to an editor/IDE you might be interested in a more
410 powerful shell environment for Win32. Your options include
416 from the Cygwin package ( http://sources.redhat.com/cygwin/ )
420 from the MKS Toolkit ( http://www.mks.com/ ), or the Bourne shell of
421 the U/WIN environment ( http://www.research.att.com/sw/tools/uwin/ )
425 ftp://ftp.astron.com/pub/tcsh/ , see also
426 http://www.primate.wisc.edu/software/csh-tcsh-book/
434 MKS and U/WIN are commercial (U/WIN is free for educational and
435 research purposes), Cygwin is covered by the GNU Public License (but
436 that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all
437 contain (in addition to the shells) a comprehensive set of standard
438 UNIX toolkit utilities.
440 If you're transferring text files between Unix and Windows using FTP
441 be sure to transfer them in ASCII mode so the ends of lines are
442 appropriately converted.
444 On Mac OS the MacPerl Application comes with a simple 32k text editor
445 that behaves like a rudimentary IDE. In contrast to the MacPerl Application
446 the MPW Perl tool can make use of the MPW Shell itself as an editor (with
453 is a full Perl development environment with full debugger support
454 ( http://www.latenightsw.com ).
458 is an editor, written and extensible in Tcl, that nonetheless has
459 built in support for several popular markup and programming languages
460 including Perl and HTML ( http://www.his.com/~jguyer/Alpha/Alpha8.html ).
462 =item BBEdit and BBEdit Lite
464 are text editors for Mac OS that have a Perl sensitivity mode
465 ( http://web.barebones.com/ ).
470 Pepper and Pe are programming language sensitive text editors for Mac
471 OS X and BeOS respectively ( http://www.hekkelman.com/ ).
473 =head2 Where can I get Perl macros for vi?
475 For a complete version of Tom Christiansen's vi configuration file,
476 see http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz ,
477 the standard benchmark file for vi emulators. The file runs best with nvi,
478 the current version of vi out of Berkeley, which incidentally can be built
479 with an embedded Perl interpreter--see http://www.cpan.org/src/misc/ .
481 =head2 Where can I get perl-mode for emacs?
483 Since Emacs version 19 patchlevel 22 or so, there have been both a
484 perl-mode.el and support for the Perl debugger built in. These should
485 come with the standard Emacs 19 distribution.
487 In the Perl source directory, you'll find a directory called "emacs",
488 which contains a cperl-mode that color-codes keywords, provides
489 context-sensitive help, and other nifty things.
491 Note that the perl-mode of emacs will have fits with C<"main'foo">
492 (single quote), and mess up the indentation and highlighting. You
493 are probably using C<"main::foo"> in new Perl code anyway, so this
494 shouldn't be an issue.
496 =head2 How can I use curses with Perl?
498 The Curses module from CPAN provides a dynamically loadable object
499 module interface to a curses library. A small demo can be found at the
500 directory http://www.cpan.org/authors/Tom_Christiansen/scripts/rep.gz ;
501 this program repeats a command and updates the screen as needed, rendering
502 B<rep ps axu> similar to B<top>.
504 =head2 How can I use X or Tk with Perl?
506 The Tk.pm module is a completely Perl-based, object-oriented interface
507 to the Tk toolkit that doesn't force you to use Tcl just to get at Tk.
508 Sx is an interface to the Athena Widget set. Both are available from
509 CPAN. See the directory
510 http://www.cpan.org/modules/by-category/08_User_Interfaces/
512 Invaluable for Perl/Tk programming are the Perl/Tk FAQ at
513 http://phaseit.net/claird/comp.lang.perl.tk/ptkFAQ.html , the Perl/Tk Reference
515 http://www.cpan.org/authors/Stephen_O_Lidie/ , and the
517 http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html .
519 =head2 How can I make my Perl program run faster?
521 The best way to do this is to come up with a better algorithm. This
522 can often make a dramatic difference. Jon Bentley's book
523 I<Programming Pearls> (that's not a misspelling!) has some good tips
524 on optimization, too. Advice on benchmarking boils down to: benchmark
525 and profile to make sure you're optimizing the right part, look for
526 better algorithms instead of microtuning your code, and when all else
527 fails consider just buying faster hardware. You will probably want to
528 read the answer to the earlier question "How do I profile my Perl
529 programs?" if you haven't done so already.
531 A different approach is to autoload seldom-used Perl code. See the
532 AutoSplit and AutoLoader modules in the standard distribution for
533 that. Or you could locate the bottleneck and think about writing just
534 that part in C, the way we used to take bottlenecks in C code and
535 write them in assembler. Similar to rewriting in C, modules that have
536 critical sections can be written in C (for instance, the PDL module
539 If you're currently linking your perl executable to a shared
540 I<libc.so>, you can often gain a 10-25% performance benefit by
541 rebuilding it to link with a static libc.a instead. This will make a
542 bigger perl executable, but your Perl programs (and programmers) may
543 thank you for it. See the F<INSTALL> file in the source distribution
544 for more information.
546 The undump program was an ancient attempt to speed up Perl program by
547 storing the already-compiled form to disk. This is no longer a viable
548 option, as it only worked on a few architectures, and wasn't a good
551 =head2 How can I make my Perl program take less memory?
553 When it comes to time-space tradeoffs, Perl nearly always prefers to
554 throw memory at a problem. Scalars in Perl use more memory than
555 strings in C, arrays take more than that, and hashes use even more. While
556 there's still a lot to be done, recent releases have been addressing
557 these issues. For example, as of 5.004, duplicate hash keys are
558 shared amongst all hashes using them, so require no reallocation.
560 In some cases, using substr() or vec() to simulate arrays can be
561 highly beneficial. For example, an array of a thousand booleans will
562 take at least 20,000 bytes of space, but it can be turned into one
563 125-byte bit vector--a considerable memory savings. The standard
564 Tie::SubstrHash module can also help for certain types of data
565 structure. If you're working with specialist data structures
566 (matrices, for instance) modules that implement these in C may use
567 less memory than equivalent Perl modules.
569 Another thing to try is learning whether your Perl was compiled with
570 the system malloc or with Perl's builtin malloc. Whichever one it
571 is, try using the other one and see whether this makes a difference.
572 Information about malloc is in the F<INSTALL> file in the source
573 distribution. You can find out whether you are using perl's malloc by
574 typing C<perl -V:usemymalloc>.
576 Of course, the best way to save memory is to not do anything to waste
577 it in the first place. Good programming practices can go a long way
584 Don't read an entire file into memory if you can process it line
585 by line. Or more concretely, use a loop like this:
604 When the files you're processing are small, it doesn't much matter which
605 way you do it, but it makes a huge difference when they start getting
608 =item * Use map and grep selectively
610 Remember that both map and grep expect a LIST argument, so doing this:
612 @wanted = grep {/pattern/} <FILE>;
614 will cause the entire file to be slurped. For large files, it's better
618 push(@wanted, $_) if /pattern/;
621 =item * Avoid unnecessary quotes and stringification
623 Don't quote large strings unless absolutely necessary:
625 my $copy = "$large_string";
627 makes 2 copies of $large_string (one for $copy and another for the
630 my $copy = $large_string;
634 Ditto for stringifying large arrays:
641 is much more memory-efficient than either
643 print join "\n", @big_array;
653 =item * Pass by reference
655 Pass arrays and hashes by reference, not by value. For one thing, it's
656 the only way to pass multiple lists or hashes (or both) in a single
657 call/return. It also avoids creating a copy of all the contents. This
658 requires some judgment, however, because any changes will be propagated
659 back to the original data. If you really want to mangle (er, modify) a
660 copy, you'll have to sacrifice the memory needed to make one.
662 =item * Tie large variables to disk.
664 For "big" data stores (i.e. ones that exceed available memory) consider
665 using one of the DB modules to store it on disk instead of in RAM. This
666 will incur a penalty in access time, but that's probably better than
667 causing your hard disk to thrash due to massive swapping.
671 =head2 Is it safe to return a reference to local or lexical data?
673 Yes. Perl's garbage collection system takes care of this so
674 everything works out right.
682 push @many, makeone();
685 print $many[4][5], "\n";
689 =head2 How can I free an array or hash so my program shrinks?
691 (contributed by Michael Carman)
693 You usually can't. Memory allocated to lexicals (i.e. my() variables)
694 cannot be reclaimed or reused even if they go out of scope. It is
695 reserved in case the variables come back into scope. Memory allocated
696 to global variables can be reused (within your program) by using
697 undef()ing and/or delete().
699 On most operating systems, memory allocated to a program can never be
700 returned to the system. That's why long-running programs sometimes re-
701 exec themselves. Some operating systems (notably, systems that use
702 mmap(2) for allocating large chunks of memory) can reclaim memory that
703 is no longer used, but on such systems, perl must be configured and
704 compiled to use the OS's malloc, not perl's.
706 In general, memory allocation and de-allocation isn't something you can
707 or should be worrying about much in Perl.
709 See also "How can I make my Perl program take less memory?"
711 =head2 How can I make my CGI script more efficient?
713 Beyond the normal measures described to make general Perl programs
714 faster or smaller, a CGI program has additional issues. It may be run
715 several times per second. Given that each time it runs it will need
716 to be re-compiled and will often allocate a megabyte or more of system
717 memory, this can be a killer. Compiling into C B<isn't going to help
718 you> because the process start-up overhead is where the bottleneck is.
720 There are two popular ways to avoid this overhead. One solution
721 involves running the Apache HTTP server (available from
722 http://www.apache.org/ ) with either of the mod_perl or mod_fastcgi
725 With mod_perl and the Apache::Registry module (distributed with
726 mod_perl), httpd will run with an embedded Perl interpreter which
727 pre-compiles your script and then executes it within the same address
728 space without forking. The Apache extension also gives Perl access to
729 the internal server API, so modules written in Perl can do just about
730 anything a module written in C can. For more on mod_perl, see
731 http://perl.apache.org/
733 With the FCGI module (from CPAN) and the mod_fastcgi
734 module (available from http://www.fastcgi.com/ ) each of your Perl
735 programs becomes a permanent CGI daemon process.
737 Both of these solutions can have far-reaching effects on your system
738 and on the way you write your CGI programs, so investigate them with
741 See http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
743 =head2 How can I hide the source for my Perl program?
745 Delete it. :-) Seriously, there are a number of (mostly
746 unsatisfactory) solutions with varying levels of "security".
748 First of all, however, you I<can't> take away read permission, because
749 the source code has to be readable in order to be compiled and
750 interpreted. (That doesn't mean that a CGI script's source is
751 readable by people on the web, though--only by people with access to
752 the filesystem.) So you have to leave the permissions at the socially
755 Some people regard this as a security problem. If your program does
756 insecure things and relies on people not knowing how to exploit those
757 insecurities, it is not secure. It is often possible for someone to
758 determine the insecure things and exploit them without viewing the
759 source. Security through obscurity, the name for hiding your bugs
760 instead of fixing them, is little security indeed.
762 You can try using encryption via source filters (Starting from Perl
763 5.8 the Filter::Simple and Filter::Util::Call modules are included in
764 the standard distribution), but any decent programmer will be able to
765 decrypt it. You can try using the byte code compiler and interpreter
766 described later in L<perlfaq3>, but the curious might still be able to
767 de-compile it. You can try using the native-code compiler described
768 later, but crackers might be able to disassemble it. These pose
769 varying degrees of difficulty to people wanting to get at your code,
770 but none can definitively conceal it (true of every language, not just
773 It is very easy to recover the source of Perl programs. You simply
774 feed the program to the perl interpreter and use the modules in
775 the B:: hierarchy. The B::Deparse module should be able to
776 defeat most attempts to hide source. Again, this is not
779 If you're concerned about people profiting from your code, then the
780 bottom line is that nothing but a restrictive license will give you
781 legal security. License your software and pepper it with threatening
782 statements like "This is unpublished proprietary software of XYZ Corp.
783 Your access to it does not give you permission to use it blah blah
784 blah." We are not lawyers, of course, so you should see a lawyer if
785 you want to be sure your license's wording will stand up in court.
787 =head2 How can I compile my Perl program into byte code or C?
789 (contributed by brian d foy)
791 In general, you can't do this. There are some things that may work
792 for your situation though. People usually ask this question
793 because they want to distribute their works without giving away
794 the source code, and most solutions trade disk space for convenience.
795 You probably won't see much of a speed increase either, since most
796 solutions simply bundle a Perl interpreter in the final product
797 (but see L<How can I make my Perl program run faster?>).
799 The Perl Archive Toolkit ( http://par.perl.org/ ) is Perl's
800 analog to Java's JAR. It's freely available and on CPAN (
801 http://search.cpan.org/dist/PAR/ ).
803 There are also some commercial products that may work for you, although
804 you have to buy a license for them.
806 The Perl Dev Kit ( http://www.activestate.com/Products/Perl_Dev_Kit/ )
807 from ActiveState can "Turn your Perl programs into ready-to-run
808 executables for HP-UX, Linux, Solaris and Windows."
810 Perl2Exe ( http://www.indigostar.com/perl2exe.htm ) is a command line
811 program for converting perl scripts to executable files. It targets both
812 Windows and unix platforms.
814 =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
818 extproc perl -S -your_switches
820 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
821 "extproc" handling). For DOS one should first invent a corresponding
822 batch file and codify it in C<ALTERNATE_SHEBANG> (see the
823 F<dosish.h> file in the source distribution for more information).
825 The Win95/NT installation, when using the ActiveState port of Perl,
826 will modify the Registry to associate the C<.pl> extension with the
827 perl interpreter. If you install another port, perhaps even building
828 your own Win95/NT Perl from the standard sources by using a Windows port
829 of gcc (e.g., with cygwin or mingw32), then you'll have to modify
830 the Registry yourself. In addition to associating C<.pl> with the
831 interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them
832 run the program C<install-linux.pl> merely by typing C<install-linux>.
834 Under "Classic" MacOS, a perl program will have the appropriate Creator and
835 Type, so that double-clicking them will invoke the MacPerl application.
836 Under Mac OS X, clickable apps can be made from any C<#!> script using Wil
837 Sanchez' DropScript utility: http://www.wsanchez.net/software/ .
839 I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
840 throw the perl interpreter into your cgi-bin directory, in order to
841 get your programs working for a web server. This is an EXTREMELY big
842 security risk. Take the time to figure out how to do it correctly.
844 =head2 Can I write useful Perl programs on the command line?
846 Yes. Read L<perlrun> for more information. Some examples follow.
847 (These assume standard Unix shell quoting rules.)
849 # sum first and last fields
850 perl -lane 'print $F[0] + $F[-1]' *
852 # identify text files
853 perl -le 'for(@ARGV) {print if -f && -T _}' *
855 # remove (most) comments from C program
856 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
858 # make file a month younger than today, defeating reaper daemons
859 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
861 # find first unused uid
862 perl -le '$i++ while getpwuid($i); print $i'
864 # display reasonable manpath
865 echo $PATH | perl -nl -072 -e '
866 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
868 OK, the last one was actually an Obfuscated Perl Contest entry. :-)
870 =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system?
872 The problem is usually that the command interpreters on those systems
873 have rather different ideas about quoting than the Unix shells under
874 which the one-liners were created. On some systems, you may have to
875 change single-quotes to double ones, which you must I<NOT> do on Unix
876 or Plan9 systems. You might also have to change a single % to a %%.
880 # Unix (including Mac OS X)
881 perl -e 'print "Hello world\n"'
884 perl -e "print \"Hello world\n\""
887 print "Hello world\n"
888 (then Run "Myscript" or Shift-Command-R)
891 perl -e 'print "Hello world\n"'
894 perl -e "print ""Hello world\n"""
896 The problem is that none of these examples are reliable: they depend on the
897 command interpreter. Under Unix, the first two often work. Under DOS,
898 it's entirely possible that neither works. If 4DOS was the command shell,
899 you'd probably have better luck like this:
901 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
903 Under the Mac, it depends which environment you are using. The MacPerl
904 shell, or MPW, is much like Unix shells in its support for several
905 quoting variants, except that it makes free use of the Mac's non-ASCII
906 characters as control characters.
908 Using qq(), q(), and qx(), instead of "double quotes", 'single
909 quotes', and `backticks`, may make one-liners easier to write.
911 There is no general solution to all of this. It is a mess.
913 [Some of this answer was contributed by Kenneth Albanowski.]
915 =head2 Where can I learn about CGI or Web programming in Perl?
917 For modules, get the CGI or LWP modules from CPAN. For textbooks,
918 see the two especially dedicated to web stuff in the question on
919 books. For problems and questions related to the web, like "Why
920 do I get 500 Errors" or "Why doesn't it run from the browser right
921 when it runs fine on the command line", see the troubleshooting
922 guides and references in L<perlfaq9> or in the CGI MetaFAQ:
924 http://www.perl.org/CGI_MetaFAQ.html
926 =head2 Where can I learn about object-oriented Perl programming?
928 A good place to start is L<perltoot>, and you can use L<perlobj>,
929 L<perlboot>, L<perltoot>, L<perltooc>, and L<perlbot> for reference.
931 A good book on OO on Perl is the "Object-Oriented Perl"
932 by Damian Conway from Manning Publications, or "Intermediate Perl"
933 by Randal Schwartz, brian d foy, and Tom Phoenix from O'Reilly Media.
935 =head2 Where can I learn about linking C with Perl?
937 If you want to call C from Perl, start with L<perlxstut>,
938 moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to
939 call Perl from C, then read L<perlembed>, L<perlcall>, and
940 L<perlguts>. Don't forget that you can learn a lot from looking at
941 how the authors of existing extension modules wrote their code and
942 solved their problems.
944 You might not need all the power of XS. The Inline::C module lets
945 you put C code directly in your Perl source. It handles all the
946 magic to make it work. You still have to learn at least some of
947 the perl API but you won't have to deal with the complexity of the
950 =head2 I've read perlembed, perlguts, etc., but I can't embed perl in my C program; what am I doing wrong?
952 Download the ExtUtils::Embed kit from CPAN and run `make test'. If
953 the tests pass, read the pods again and again and again. If they
954 fail, see L<perlbug> and send a bug report with the output of
955 C<make test TEST_VERBOSE=1> along with C<perl -V>.
957 =head2 When I tried to run my script, I got this message. What does it mean?
959 A complete list of Perl's error messages and warnings with explanatory
960 text can be found in L<perldiag>. You can also use the splain program
961 (distributed with Perl) to explain the error messages:
963 perl program 2>diag.out
964 splain [-v] [-p] diag.out
966 or change your program to explain the messages for you:
972 use diagnostics -verbose;
974 =head2 What's MakeMaker?
976 (contributed by brian d foy)
978 The C<ExtUtils::MakeMaker> module, better known simply as "MakeMaker",
979 turns a Perl script, typically called C<Makefile.PL>, into a Makefile.
980 The unix tool C<make> uses this file to manage dependencies and actions
981 to process and install a Perl distribution.
985 Revision: $Revision: 7875 $
987 Date: $Date: 2006-10-04 22:39:26 +0200 (mer, 04 oct 2006) $
989 See L<perlfaq> for source control details and availability.
991 =head1 AUTHOR AND COPYRIGHT
993 Copyright (c) 1997-2006 Tom Christiansen, Nathan Torkington, and
994 other authors as noted. All rights reserved.
996 This documentation is free; you can redistribute it and/or modify it
997 under the same terms as Perl itself.
999 Irrespective of its distribution, all code examples here are in the public
1000 domain. You are permitted and encouraged to use this code and any
1001 derivatives thereof in your own programs for fun or for profit as you
1002 see fit. A simple comment in the code giving credit to the FAQ would
1003 be courteous but is not required.