3 perlfaq3 - Programming Tools ($Revision: 1.52 $, $Date: 2005/10/13 19:43:13 $)
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
46 shell that combines the interactive nature of a Unix shell with the
47 power of Perl. The goal is a full featured shell that behaves as
48 expected for normal shell activity and uses Perl syntax and
49 functionality for control-flow statements and other things.
50 You can get psh at 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
59 from the source distribution is simplistic and uninteresting, but
60 may still be what you want.
62 =head2 How do I find which modules are installed on my system?
64 You can use the ExtUtils::Installed module to show all
65 installed distributions, although it can take awhile to do
66 its magic. The standard library which comes with Perl just
67 shows up as "Perl" (although you can get those with
70 use ExtUtils::Installed;
72 my $inst = ExtUtils::Installed->new();
73 my @modules = $inst->modules();
75 If you want a list of all of the Perl module filenames, you
76 can use File::Find::Rule.
80 my @files = File::Find::Rule->file()->name( '*.pm' )->in( @INC );
82 If you do not have that module, you can do the same thing
83 with File::Find which is part of the standard library.
89 sub { push @files, $File::Find::name if -f $File::Find::name && /\.pm$/ },
93 print "$_\n" for @files;
95 If you simply need to quickly check to see if a module is
96 available, you can check for its documentation. If you can
97 read the documentation the module is most likely installed.
98 If you cannot read the documentation, the module might not
99 have any (in rare cases).
101 prompt% perldoc Module::Name
103 You can also try to include the module in a one-liner to see if
106 perl -MModule::Name -e1
108 =head2 How do I debug my Perl programs?
110 Have you tried C<use warnings> or used C<-w>? They enable warnings
111 to detect dubious practices.
113 Have you tried C<use strict>? It prevents you from using symbolic
114 references, makes you predeclare any subroutines that you call as bare
115 words, and (probably most importantly) forces you to predeclare your
116 variables with C<my>, C<our>, or C<use vars>.
118 Did you check the return values of each and every system call? The operating
119 system (and thus Perl) tells you whether they worked, and if not
122 open(FH, "> /etc/cantwrite")
123 or die "Couldn't write to /etc/cantwrite: $!\n";
125 Did you read L<perltrap>? It's full of gotchas for old and new Perl
126 programmers and even has sections for those of you who are upgrading
127 from languages like I<awk> and I<C>.
129 Have you tried the Perl debugger, described in L<perldebug>? You can
130 step through your program and see what it's doing and thus work out
131 why what it's doing isn't what it should be doing.
133 =head2 How do I profile my Perl programs?
135 You should get the Devel::DProf module from the standard distribution
136 (or separately on CPAN) and also use Benchmark.pm from the standard
137 distribution. The Benchmark module lets you time specific portions of
138 your code, while Devel::DProf gives detailed breakdowns of where your
139 code spends its time.
141 Here's a sample use of Benchmark:
145 @junk = `cat /etc/motd`;
149 'map' => sub { my @a = @junk;
152 'for' => sub { my @a = @junk;
157 This is what it prints (on one machine--your results will be dependent
158 on your hardware, operating system, and the load on your machine):
160 Benchmark: timing 10000 iterations of for, map...
161 for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu)
162 map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu)
164 Be aware that a good benchmark is very hard to write. It only tests the
165 data you give it and proves little about the differing complexities
166 of contrasting algorithms.
168 =head2 How do I cross-reference my Perl programs?
170 The B::Xref module can be used to generate cross-reference reports
173 perl -MO=Xref[,OPTIONS] scriptname.plx
175 =head2 Is there a pretty-printer (formatter) for Perl?
177 Perltidy is a Perl script which indents and reformats Perl scripts
178 to make them easier to read by trying to follow the rules of the
179 L<perlstyle>. If you write Perl scripts, or spend much time reading
180 them, you will probably find it useful. It is available at
181 http://perltidy.sourceforge.net
183 Of course, if you simply follow the guidelines in L<perlstyle>,
184 you shouldn't need to reformat. The habit of formatting your code
185 as you write it will help prevent bugs. Your editor can and should
186 help you with this. The perl-mode or newer cperl-mode for emacs
187 can provide remarkable amounts of help with most (but not all)
188 code, and even less programmable editors can provide significant
189 assistance. Tom Christiansen and many other VI users swear by
190 the following settings in vi and its clones:
195 Put that in your F<.exrc> file (replacing the caret characters
196 with control characters) and away you go. In insert mode, ^T is
197 for indenting, ^D is for undenting, and ^O is for blockdenting--
198 as it were. A more complete example, with comments, can be found at
199 http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz
201 The a2ps http://www-inf.enst.fr/%7Edemaille/a2ps/black+white.ps.gz does
202 lots of things related to generating nicely printed output of
203 documents, as does enscript at http://people.ssh.fi/mtr/genscript/ .
205 =head2 Is there a ctags for Perl?
207 (contributed by brian d foy)
209 Exuberent ctags supports Perl: http://ctags.sourceforge.net/
211 You might also try pltags: http://www.mscha.com/pltags.zip
213 =head2 Is there an IDE or Windows Perl Editor?
215 Perl programs are just plain text, so any editor will do.
217 If you're on Unix, you already have an IDE--Unix itself. The UNIX
218 philosophy is the philosophy of several small tools that each do one
219 thing and do it well. It's like a carpenter's toolbox.
221 If you want an IDE, check the following (in alphabetical order, not
222 order of preference):
228 http://e-p-i-c.sf.net/
230 The Eclipse Perl Integration Project integrates Perl
231 editing/debugging with Eclipse.
235 http://www.enginsite.com/
237 Perl Editor by EngInSite is a complete integrated development
238 environment (IDE) for creating, testing, and debugging Perl scripts;
239 the tool runs on Windows 9x/NT/2000/XP or later.
243 http://www.ActiveState.com/Products/Komodo/
245 ActiveState's cross-platform (as of October 2004, that's Windows, Linux,
246 and Solaris), multi-language IDE has Perl support, including a regular expression
247 debugger and remote debugging.
251 http://open-perl-ide.sourceforge.net/
253 Open Perl IDE is an integrated development environment for writing
254 and debugging Perl scripts with ActiveState's ActivePerl distribution
255 under Windows 95/98/NT/2000.
259 http://www.optiperl.com/
261 OptiPerl is a Windows IDE with simulated CGI environment, including
262 debugger and syntax highlighting editor.
266 http://www.solutionsoft.com/perl.htm
268 PerlBuidler is an integrated development environment for Windows that
269 supports Perl development.
273 http://helpconsulting.net/visiperl/
275 From Help Consulting, for Windows.
279 http://www.activestate.com/Products/Visual_Perl/
281 Visual Perl is a Visual Studio.NET plug-in from ActiveState.
285 http://www.zeusedit.com/lookmain.html
287 Zeus for Window is another Win32 multi-language editor/IDE
288 that comes with support for Perl:
292 For editors: if you're on Unix you probably have vi or a vi clone
293 already, and possibly an emacs too, so you may not need to download
294 anything. In any emacs the cperl-mode (M-x cperl-mode) gives you
295 perhaps the best available Perl editing mode in any editor.
297 If you are using Windows, you can use any editor that lets you work
298 with plain text, such as NotePad or WordPad. Word processors, such as
299 Microsoft Word or WordPerfect, typically do not work since they insert
300 all sorts of behind-the-scenes information, although some allow you to
301 save files as "Text Only". You can also download text editors designed
302 specifically for programming, such as Textpad (
303 http://www.textpad.com/ ) and UltraEdit ( http://www.ultraedit.com/ ),
306 If you are using MacOS, the same concerns apply. MacPerl (for Classic
307 environments) comes with a simple editor. Popular external editors are
308 BBEdit ( http://www.bbedit.com/ ) or Alpha (
309 http://www.his.com/~jguyer/Alpha/Alpha8.html ). MacOS X users can use
310 Unix editors as well. Neil Bowers (the man behind Geekcruises) has a
311 list of Mac editors that can handle Perl (
312 http://www.neilbowers.org/macperleditors.html ).
318 http://www.gnu.org/software/emacs/windows/ntemacs.html
322 http://www.microemacs.de/
326 http://www.xemacs.org/Download/index.html
330 http://space.mit.edu/~davis/jed/
334 or a vi clone such as
340 ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/
344 http://dickey.his.com/vile/vile.html
352 For vi lovers in general, Windows or elsewhere:
354 http://www.thomer.com/thomer/vi/vi.html
356 nvi ( http://www.bostic.com/vi/ , available from CPAN in src/misc/) is
357 yet another vi clone, unfortunately not available for Windows, but in
358 UNIX platforms you might be interested in trying it out, firstly because
359 strictly speaking it is not a vi clone, it is the real vi, or the new
360 incarnation of it, and secondly because you can embed Perl inside it
361 to use Perl as the scripting language. nvi is not alone in this,
362 though: at least also vim and vile offer an embedded Perl.
364 The following are Win32 multilanguage editor/IDESs that support Perl:
370 http://www.borland.com/codewright/
374 http://www.MultiEdit.com/
378 http://www.slickedit.com/
382 There is also a toyedit Text widget based editor written in Perl
383 that is distributed with the Tk module on CPAN. The ptkdb
384 ( http://world.std.com/~aep/ptkdb/ ) is a Perl/tk based debugger that
385 acts as a development environment of sorts. Perl Composer
386 ( http://perlcomposer.sourceforge.net/ ) is an IDE for Perl/Tk
389 In addition to an editor/IDE you might be interested in a more
390 powerful shell environment for Win32. Your options include
396 from the Cygwin package ( http://sources.redhat.com/cygwin/ )
400 from the MKS Toolkit ( http://www.mks.com/ ), or the Bourne shell of
401 the U/WIN environment ( http://www.research.att.com/sw/tools/uwin/ )
405 ftp://ftp.astron.com/pub/tcsh/ , see also
406 http://www.primate.wisc.edu/software/csh-tcsh-book/
410 ftp://ftp.blarg.net/users/amol/zsh/ , see also http://www.zsh.org/
414 MKS and U/WIN are commercial (U/WIN is free for educational and
415 research purposes), Cygwin is covered by the GNU Public License (but
416 that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all
417 contain (in addition to the shells) a comprehensive set of standard
418 UNIX toolkit utilities.
420 If you're transferring text files between Unix and Windows using FTP
421 be sure to transfer them in ASCII mode so the ends of lines are
422 appropriately converted.
424 On Mac OS the MacPerl Application comes with a simple 32k text editor
425 that behaves like a rudimentary IDE. In contrast to the MacPerl Application
426 the MPW Perl tool can make use of the MPW Shell itself as an editor (with
433 is a full Perl development environment with full debugger support
434 ( http://www.latenightsw.com ).
438 is an editor, written and extensible in Tcl, that nonetheless has
439 built in support for several popular markup and programming languages
440 including Perl and HTML ( http://www.his.com/~jguyer/Alpha/Alpha8.html ).
442 =item BBEdit and BBEdit Lite
444 are text editors for Mac OS that have a Perl sensitivity mode
445 ( http://web.barebones.com/ ).
450 Pepper and Pe are programming language sensitive text editors for Mac
451 OS X and BeOS respectively ( http://www.hekkelman.com/ ).
453 =head2 Where can I get Perl macros for vi?
455 For a complete version of Tom Christiansen's vi configuration file,
456 see http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz ,
457 the standard benchmark file for vi emulators. The file runs best with nvi,
458 the current version of vi out of Berkeley, which incidentally can be built
459 with an embedded Perl interpreter--see http://www.cpan.org/src/misc/ .
461 =head2 Where can I get perl-mode for emacs?
463 Since Emacs version 19 patchlevel 22 or so, there have been both a
464 perl-mode.el and support for the Perl debugger built in. These should
465 come with the standard Emacs 19 distribution.
467 In the Perl source directory, you'll find a directory called "emacs",
468 which contains a cperl-mode that color-codes keywords, provides
469 context-sensitive help, and other nifty things.
471 Note that the perl-mode of emacs will have fits with C<"main'foo">
472 (single quote), and mess up the indentation and highlighting. You
473 are probably using C<"main::foo"> in new Perl code anyway, so this
474 shouldn't be an issue.
476 =head2 How can I use curses with Perl?
478 The Curses module from CPAN provides a dynamically loadable object
479 module interface to a curses library. A small demo can be found at the
480 directory http://www.cpan.org/authors/Tom_Christiansen/scripts/rep.gz ;
481 this program repeats a command and updates the screen as needed, rendering
482 B<rep ps axu> similar to B<top>.
484 =head2 How can I use X or Tk with Perl?
486 Tk is a completely Perl-based, object-oriented interface to the Tk toolkit
487 that doesn't force you to use Tcl just to get at Tk. Sx is an interface
488 to the Athena Widget set. Both are available from CPAN. See the
489 directory http://www.cpan.org/modules/by-category/08_User_Interfaces/
491 Invaluable for Perl/Tk programming are the Perl/Tk FAQ at
492 http://phaseit.net/claird/comp.lang.perl.tk/ptkFAQ.html , the Perl/Tk Reference
494 http://www.cpan.org/authors/Stephen_O_Lidie/ , and the
496 http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html .
498 =head2 How can I make my Perl program run faster?
500 The best way to do this is to come up with a better algorithm. This
501 can often make a dramatic difference. Jon Bentley's book
502 I<Programming Pearls> (that's not a misspelling!) has some good tips
503 on optimization, too. Advice on benchmarking boils down to: benchmark
504 and profile to make sure you're optimizing the right part, look for
505 better algorithms instead of microtuning your code, and when all else
506 fails consider just buying faster hardware. You will probably want to
507 read the answer to the earlier question "How do I profile my Perl
508 programs?" if you haven't done so already.
510 A different approach is to autoload seldom-used Perl code. See the
511 AutoSplit and AutoLoader modules in the standard distribution for
512 that. Or you could locate the bottleneck and think about writing just
513 that part in C, the way we used to take bottlenecks in C code and
514 write them in assembler. Similar to rewriting in C, modules that have
515 critical sections can be written in C (for instance, the PDL module
518 If you're currently linking your perl executable to a shared
519 I<libc.so>, you can often gain a 10-25% performance benefit by
520 rebuilding it to link with a static libc.a instead. This will make a
521 bigger perl executable, but your Perl programs (and programmers) may
522 thank you for it. See the F<INSTALL> file in the source distribution
523 for more information.
525 The undump program was an ancient attempt to speed up Perl program by
526 storing the already-compiled form to disk. This is no longer a viable
527 option, as it only worked on a few architectures, and wasn't a good
530 =head2 How can I make my Perl program take less memory?
532 When it comes to time-space tradeoffs, Perl nearly always prefers to
533 throw memory at a problem. Scalars in Perl use more memory than
534 strings in C, arrays take more than that, and hashes use even more. While
535 there's still a lot to be done, recent releases have been addressing
536 these issues. For example, as of 5.004, duplicate hash keys are
537 shared amongst all hashes using them, so require no reallocation.
539 In some cases, using substr() or vec() to simulate arrays can be
540 highly beneficial. For example, an array of a thousand booleans will
541 take at least 20,000 bytes of space, but it can be turned into one
542 125-byte bit vector--a considerable memory savings. The standard
543 Tie::SubstrHash module can also help for certain types of data
544 structure. If you're working with specialist data structures
545 (matrices, for instance) modules that implement these in C may use
546 less memory than equivalent Perl modules.
548 Another thing to try is learning whether your Perl was compiled with
549 the system malloc or with Perl's builtin malloc. Whichever one it
550 is, try using the other one and see whether this makes a difference.
551 Information about malloc is in the F<INSTALL> file in the source
552 distribution. You can find out whether you are using perl's malloc by
553 typing C<perl -V:usemymalloc>.
555 Of course, the best way to save memory is to not do anything to waste
556 it in the first place. Good programming practices can go a long way
563 Don't read an entire file into memory if you can process it line
564 by line. Or more concretely, use a loop like this:
583 When the files you're processing are small, it doesn't much matter which
584 way you do it, but it makes a huge difference when they start getting
587 =item * Use map and grep selectively
589 Remember that both map and grep expect a LIST argument, so doing this:
591 @wanted = grep {/pattern/} <FILE>;
593 will cause the entire file to be slurped. For large files, it's better
597 push(@wanted, $_) if /pattern/;
600 =item * Avoid unnecessary quotes and stringification
602 Don't quote large strings unless absolutely necessary:
604 my $copy = "$large_string";
606 makes 2 copies of $large_string (one for $copy and another for the
609 my $copy = $large_string;
613 Ditto for stringifying large arrays:
620 is much more memory-efficient than either
622 print join "\n", @big_array;
632 =item * Pass by reference
634 Pass arrays and hashes by reference, not by value. For one thing, it's
635 the only way to pass multiple lists or hashes (or both) in a single
636 call/return. It also avoids creating a copy of all the contents. This
637 requires some judgment, however, because any changes will be propagated
638 back to the original data. If you really want to mangle (er, modify) a
639 copy, you'll have to sacrifice the memory needed to make one.
641 =item * Tie large variables to disk.
643 For "big" data stores (i.e. ones that exceed available memory) consider
644 using one of the DB modules to store it on disk instead of in RAM. This
645 will incur a penalty in access time, but that's probably better than
646 causing your hard disk to thrash due to massive swapping.
650 =head2 Is it safe to return a reference to local or lexical data?
652 Yes. Perl's garbage collection system takes care of this so
653 everything works out right.
661 push @many, makeone();
664 print $many[4][5], "\n";
668 =head2 How can I free an array or hash so my program shrinks?
670 (contributed by Michael Carman)
672 You usually can't. Memory allocated to lexicals (i.e. my() variables)
673 cannot be reclaimed or reused even if they go out of scope. It is
674 reserved in case the variables come back into scope. Memory allocated
675 to global variables can be reused (within your program) by using
676 undef()ing and/or delete().
678 On most operating systems, memory allocated to a program can never be
679 returned to the system. That's why long-running programs sometimes re-
680 exec themselves. Some operating systems (notably, systems that use
681 mmap(2) for allocating large chunks of memory) can reclaim memory that
682 is no longer used, but on such systems, perl must be configured and
683 compiled to use the OS's malloc, not perl's.
685 In general, memory allocation and de-allocation isn't something you can
686 or should be worrying about much in Perl.
688 See also "How can I make my Perl program take less memory?"
690 =head2 How can I make my CGI script more efficient?
692 Beyond the normal measures described to make general Perl programs
693 faster or smaller, a CGI program has additional issues. It may be run
694 several times per second. Given that each time it runs it will need
695 to be re-compiled and will often allocate a megabyte or more of system
696 memory, this can be a killer. Compiling into C B<isn't going to help
697 you> because the process start-up overhead is where the bottleneck is.
699 There are two popular ways to avoid this overhead. One solution
700 involves running the Apache HTTP server (available from
701 http://www.apache.org/ ) with either of the mod_perl or mod_fastcgi
704 With mod_perl and the Apache::Registry module (distributed with
705 mod_perl), httpd will run with an embedded Perl interpreter which
706 pre-compiles your script and then executes it within the same address
707 space without forking. The Apache extension also gives Perl access to
708 the internal server API, so modules written in Perl can do just about
709 anything a module written in C can. For more on mod_perl, see
710 http://perl.apache.org/
712 With the FCGI module (from CPAN) and the mod_fastcgi
713 module (available from http://www.fastcgi.com/ ) each of your Perl
714 programs becomes a permanent CGI daemon process.
716 Both of these solutions can have far-reaching effects on your system
717 and on the way you write your CGI programs, so investigate them with
720 See http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
722 =head2 How can I hide the source for my Perl program?
724 Delete it. :-) Seriously, there are a number of (mostly
725 unsatisfactory) solutions with varying levels of "security".
727 First of all, however, you I<can't> take away read permission, because
728 the source code has to be readable in order to be compiled and
729 interpreted. (That doesn't mean that a CGI script's source is
730 readable by people on the web, though--only by people with access to
731 the filesystem.) So you have to leave the permissions at the socially
734 Some people regard this as a security problem. If your program does
735 insecure things and relies on people not knowing how to exploit those
736 insecurities, it is not secure. It is often possible for someone to
737 determine the insecure things and exploit them without viewing the
738 source. Security through obscurity, the name for hiding your bugs
739 instead of fixing them, is little security indeed.
741 You can try using encryption via source filters (Starting from Perl
742 5.8 the Filter::Simple and Filter::Util::Call modules are included in
743 the standard distribution), but any decent programmer will be able to
744 decrypt it. You can try using the byte code compiler and interpreter
745 described below, but the curious might still be able to de-compile it.
746 You can try using the native-code compiler described below, but
747 crackers might be able to disassemble it. These pose varying degrees
748 of difficulty to people wanting to get at your code, but none can
749 definitively conceal it (true of every language, not just Perl).
751 It is very easy to recover the source of Perl programs. You simply
752 feed the program to the perl interpreter and use the modules in
753 the B:: hierarchy. The B::Deparse module should be able to
754 defeat most attempts to hide source. Again, this is not
757 If you're concerned about people profiting from your code, then the
758 bottom line is that nothing but a restrictive license will give you
759 legal security. License your software and pepper it with threatening
760 statements like "This is unpublished proprietary software of XYZ Corp.
761 Your access to it does not give you permission to use it blah blah
762 blah." We are not lawyers, of course, so you should see a lawyer if
763 you want to be sure your license's wording will stand up in court.
765 =head2 How can I compile my Perl program into byte code or C?
767 (contributed by brian d foy)
769 In general, you can't do this. There are some things that may work
770 for your situation though. People usually ask this question
771 because they want to distribute their works without giving away
772 the source code, and most solutions trade disk space for convenience.
773 You probably won't see much of a speed increase either, since most
774 solutions simply bundle a Perl interpreter in the final product
775 (but see L<How can I make my Perl program run faster?>).
777 The Perl Archive Toolkit ( http://par.perl.org/index.cgi ) is Perl's
778 analog to Java's JAR. It's freely available and on CPAN (
779 http://search.cpan.org/dist/PAR/ ).
781 The B::* namespace, often called "the Perl compiler", but is really a way
782 for Perl programs to peek at its innards rather than create pre-compiled
783 versions of your program. However. the B::Bytecode module can turn your
784 script into a bytecode format that could be loaded later by the
785 ByteLoader module and executed as a regular Perl script.
787 There are also some commercial products that may work for you, although
788 you have to buy a license for them.
790 The Perl Dev Kit ( http://www.activestate.com/Products/Perl_Dev_Kit/ )
791 from ActiveState can "Turn your Perl programs into ready-to-run
792 executables for HP-UX, Linux, Solaris and Windows."
794 Perl2Exe ( http://www.indigostar.com/perl2exe.htm ) is a command line
795 program for converting perl scripts to executable files. It targets both
796 Windows and unix platforms.
798 =head2 How can I compile Perl into Java?
800 You can also integrate Java and Perl with the
801 Perl Resource Kit from O'Reilly Media. See
802 http://www.oreilly.com/catalog/prkunix/ .
804 Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in
805 development, allows Perl code to be called from Java. See jpl/README
806 in the Perl source tree.
808 =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
812 extproc perl -S -your_switches
814 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
815 "extproc" handling). For DOS one should first invent a corresponding
816 batch file and codify it in C<ALTERNATE_SHEBANG> (see the
817 F<dosish.h> file in the source distribution for more information).
819 The Win95/NT installation, when using the ActiveState port of Perl,
820 will modify the Registry to associate the C<.pl> extension with the
821 perl interpreter. If you install another port, perhaps even building
822 your own Win95/NT Perl from the standard sources by using a Windows port
823 of gcc (e.g., with cygwin or mingw32), then you'll have to modify
824 the Registry yourself. In addition to associating C<.pl> with the
825 interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them
826 run the program C<install-linux.pl> merely by typing C<install-linux>.
828 Under "Classic" MacOS, a perl program will have the appropriate Creator and
829 Type, so that double-clicking them will invoke the MacPerl application.
830 Under Mac OS X, clickable apps can be made from any C<#!> script using Wil
831 Sanchez' DropScript utility: http://www.wsanchez.net/software/ .
833 I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
834 throw the perl interpreter into your cgi-bin directory, in order to
835 get your programs working for a web server. This is an EXTREMELY big
836 security risk. Take the time to figure out how to do it correctly.
838 =head2 Can I write useful Perl programs on the command line?
840 Yes. Read L<perlrun> for more information. Some examples follow.
841 (These assume standard Unix shell quoting rules.)
843 # sum first and last fields
844 perl -lane 'print $F[0] + $F[-1]' *
846 # identify text files
847 perl -le 'for(@ARGV) {print if -f && -T _}' *
849 # remove (most) comments from C program
850 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
852 # make file a month younger than today, defeating reaper daemons
853 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
855 # find first unused uid
856 perl -le '$i++ while getpwuid($i); print $i'
858 # display reasonable manpath
859 echo $PATH | perl -nl -072 -e '
860 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
862 OK, the last one was actually an Obfuscated Perl Contest entry. :-)
864 =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system?
866 The problem is usually that the command interpreters on those systems
867 have rather different ideas about quoting than the Unix shells under
868 which the one-liners were created. On some systems, you may have to
869 change single-quotes to double ones, which you must I<NOT> do on Unix
870 or Plan9 systems. You might also have to change a single % to a %%.
875 perl -e 'print "Hello world\n"'
878 perl -e "print \"Hello world\n\""
881 print "Hello world\n"
882 (then Run "Myscript" or Shift-Command-R)
885 perl -e 'print "Hello world\n"'
888 perl -e "print ""Hello world\n"""
890 The problem is that none of these examples are reliable: they depend on the
891 command interpreter. Under Unix, the first two often work. Under DOS,
892 it's entirely possible that neither works. If 4DOS was the command shell,
893 you'd probably have better luck like this:
895 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
897 Under the Mac, it depends which environment you are using. The MacPerl
898 shell, or MPW, is much like Unix shells in its support for several
899 quoting variants, except that it makes free use of the Mac's non-ASCII
900 characters as control characters.
902 Using qq(), q(), and qx(), instead of "double quotes", 'single
903 quotes', and `backticks`, may make one-liners easier to write.
905 There is no general solution to all of this. It is a mess.
907 [Some of this answer was contributed by Kenneth Albanowski.]
909 =head2 Where can I learn about CGI or Web programming in Perl?
911 For modules, get the CGI or LWP modules from CPAN. For textbooks,
912 see the two especially dedicated to web stuff in the question on
913 books. For problems and questions related to the web, like "Why
914 do I get 500 Errors" or "Why doesn't it run from the browser right
915 when it runs fine on the command line", see the troubleshooting
916 guides and references in L<perlfaq9> or in the CGI MetaFAQ:
918 http://www.perl.org/CGI_MetaFAQ.html
920 =head2 Where can I learn about object-oriented Perl programming?
922 A good place to start is L<perltoot>, and you can use L<perlobj>,
923 L<perlboot>, L<perltoot>, L<perltooc>, and L<perlbot> for reference.
925 A good book on OO on Perl is the "Object-Oriented Perl"
926 by Damian Conway from Manning Publications, or "Learning Perl
927 References, Objects, & Modules" by Randal Schwartz and Tom
928 Phoenix from O'Reilly Media.
930 =head2 Where can I learn about linking C with Perl?
932 If you want to call C from Perl, start with L<perlxstut>,
933 moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to
934 call Perl from C, then read L<perlembed>, L<perlcall>, and
935 L<perlguts>. Don't forget that you can learn a lot from looking at
936 how the authors of existing extension modules wrote their code and
937 solved their problems.
939 You might not need all the power of XS. The Inline::C module lets
940 you put C code directly in your Perl source. It handles all the
941 magic to make it work. You still have to learn at least some of
942 the perl API but you won't have to deal with the complexity of the
945 =head2 I've read perlembed, perlguts, etc., but I can't embed perl in my C program; what am I doing wrong?
947 Download the ExtUtils::Embed kit from CPAN and run `make test'. If
948 the tests pass, read the pods again and again and again. If they
949 fail, see L<perlbug> and send a bug report with the output of
950 C<make test TEST_VERBOSE=1> along with C<perl -V>.
952 =head2 When I tried to run my script, I got this message. What does it mean?
954 A complete list of Perl's error messages and warnings with explanatory
955 text can be found in L<perldiag>. You can also use the splain program
956 (distributed with Perl) to explain the error messages:
958 perl program 2>diag.out
959 splain [-v] [-p] diag.out
961 or change your program to explain the messages for you:
967 use diagnostics -verbose;
969 =head2 What's MakeMaker?
971 This module (part of the standard Perl distribution) is designed to
972 write a Makefile for an extension module from a Makefile.PL. For more
973 information, see L<ExtUtils::MakeMaker>.
975 =head1 AUTHOR AND COPYRIGHT
977 Copyright (c) 1997-2005 Tom Christiansen, Nathan Torkington, and
978 other authors as noted. All rights reserved.
980 This documentation is free; you can redistribute it and/or modify it
981 under the same terms as Perl itself.
983 Irrespective of its distribution, all code examples here are in the public
984 domain. You are permitted and encouraged to use this code and any
985 derivatives thereof in your own programs for fun or for profit as you
986 see fit. A simple comment in the code giving credit to the FAQ would
987 be courteous but is not required.