3 perlfaq3 - Programming Tools ($Revision: 1.51 $, $Date: 2005/08/10 15:56:39 $)
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://www.focusresearch.com/gregor/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.
88 find sub { push @files, $File::Find::name if -f _ && /\.pm$/ },
91 print join "\n", @files;
93 If you simply need to quickly check to see if a module is
94 available, you can check for its documentation. If you can
95 read the documentation the module is most likely installed.
96 If you cannot read the documentation, the module might not
97 have any (in rare cases).
99 prompt% perldoc Module::Name
101 You can also try to include the module in a one-liner to see if
104 perl -MModule::Name -e1
106 =head2 How do I debug my Perl programs?
108 Have you tried C<use warnings> or used C<-w>? They enable warnings
109 to detect dubious practices.
111 Have you tried C<use strict>? It prevents you from using symbolic
112 references, makes you predeclare any subroutines that you call as bare
113 words, and (probably most importantly) forces you to predeclare your
114 variables with C<my>, C<our>, or C<use vars>.
116 Did you check the return values of each and every system call? The operating
117 system (and thus Perl) tells you whether they worked, and if not
120 open(FH, "> /etc/cantwrite")
121 or die "Couldn't write to /etc/cantwrite: $!\n";
123 Did you read L<perltrap>? It's full of gotchas for old and new Perl
124 programmers and even has sections for those of you who are upgrading
125 from languages like I<awk> and I<C>.
127 Have you tried the Perl debugger, described in L<perldebug>? You can
128 step through your program and see what it's doing and thus work out
129 why what it's doing isn't what it should be doing.
131 =head2 How do I profile my Perl programs?
133 You should get the Devel::DProf module from the standard distribution
134 (or separately on CPAN) and also use Benchmark.pm from the standard
135 distribution. The Benchmark module lets you time specific portions of
136 your code, while Devel::DProf gives detailed breakdowns of where your
137 code spends its time.
139 Here's a sample use of Benchmark:
143 @junk = `cat /etc/motd`;
147 'map' => sub { my @a = @junk;
150 'for' => sub { my @a = @junk;
155 This is what it prints (on one machine--your results will be dependent
156 on your hardware, operating system, and the load on your machine):
158 Benchmark: timing 10000 iterations of for, map...
159 for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu)
160 map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu)
162 Be aware that a good benchmark is very hard to write. It only tests the
163 data you give it and proves little about the differing complexities
164 of contrasting algorithms.
166 =head2 How do I cross-reference my Perl programs?
168 The B::Xref module can be used to generate cross-reference reports
171 perl -MO=Xref[,OPTIONS] scriptname.plx
173 =head2 Is there a pretty-printer (formatter) for Perl?
175 Perltidy is a Perl script which indents and reformats Perl scripts
176 to make them easier to read by trying to follow the rules of the
177 L<perlstyle>. If you write Perl scripts, or spend much time reading
178 them, you will probably find it useful. It is available at
179 http://perltidy.sourceforge.net
181 Of course, if you simply follow the guidelines in L<perlstyle>,
182 you shouldn't need to reformat. The habit of formatting your code
183 as you write it will help prevent bugs. Your editor can and should
184 help you with this. The perl-mode or newer cperl-mode for emacs
185 can provide remarkable amounts of help with most (but not all)
186 code, and even less programmable editors can provide significant
187 assistance. Tom Christiansen and many other VI users swear by
188 the following settings in vi and its clones:
193 Put that in your F<.exrc> file (replacing the caret characters
194 with control characters) and away you go. In insert mode, ^T is
195 for indenting, ^D is for undenting, and ^O is for blockdenting--
196 as it were. A more complete example, with comments, can be found at
197 http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz
199 The a2ps http://www-inf.enst.fr/%7Edemaille/a2ps/black+white.ps.gz does
200 lots of things related to generating nicely printed output of
201 documents, as does enscript at http://people.ssh.fi/mtr/genscript/ .
203 =head2 Is there a ctags for Perl?
205 (contributed by brian d foy)
207 Exuberent ctags supports Perl: http://ctags.sourceforge.net/
209 You might also try pltags: http://www.mscha.com/pltags.zip
211 =head2 Is there an IDE or Windows Perl Editor?
213 Perl programs are just plain text, so any editor will do.
215 If you're on Unix, you already have an IDE--Unix itself. The UNIX
216 philosophy is the philosophy of several small tools that each do one
217 thing and do it well. It's like a carpenter's toolbox.
219 If you want an IDE, check the following (in alphabetical order, not
220 order of preference):
226 http://e-p-i-c.sf.net/
228 The Eclipse Perl Integration Project integrates Perl
229 editing/debugging with Eclipse.
233 http://www.enginsite.com/
235 Perl Editor by EngInSite is a complete integrated development
236 environment (IDE) for creating, testing, and debugging Perl scripts;
237 the tool runs on Windows 9x/NT/2000/XP or later.
241 http://www.ActiveState.com/Products/Komodo/
243 ActiveState's cross-platform (as of October 2004, that's Windows, Linux,
244 and Solaris), multi-language IDE has Perl support, including a regular expression
245 debugger and remote debugging.
249 http://open-perl-ide.sourceforge.net/
251 Open Perl IDE is an integrated development environment for writing
252 and debugging Perl scripts with ActiveState's ActivePerl distribution
253 under Windows 95/98/NT/2000.
257 http://www.optiperl.com/
259 OptiPerl is a Windows IDE with simulated CGI environment, including
260 debugger and syntax highlighting editor.
264 http://www.solutionsoft.com/perl.htm
266 PerlBuidler is an integrated development environment for Windows that
267 supports Perl development.
271 http://helpconsulting.net/visiperl/
273 From Help Consulting, for Windows.
277 http://www.activestate.com/Products/Visual_Perl/
279 Visual Perl is a Visual Studio.NET plug-in from ActiveState.
283 http://www.zeusedit.com/lookmain.html
285 Zeus for Window is another Win32 multi-language editor/IDE
286 that comes with support for Perl:
290 For editors: if you're on Unix you probably have vi or a vi clone
291 already, and possibly an emacs too, so you may not need to download
292 anything. In any emacs the cperl-mode (M-x cperl-mode) gives you
293 perhaps the best available Perl editing mode in any editor.
295 If you are using Windows, you can use any editor that lets you work
296 with plain text, such as NotePad or WordPad. Word processors, such as
297 Microsoft Word or WordPerfect, typically do not work since they insert
298 all sorts of behind-the-scenes information, although some allow you to
299 save files as "Text Only". You can also download text editors designed
300 specifically for programming, such as Textpad (
301 http://www.textpad.com/ ) and UltraEdit ( http://www.ultraedit.com/ ),
304 If you are using MacOS, the same concerns apply. MacPerl (for Classic
305 environments) comes with a simple editor. Popular external editors are
306 BBEdit ( http://www.bbedit.com/ ) or Alpha (
307 http://www.his.com/~jguyer/Alpha/Alpha8.html ). MacOS X users can use
308 Unix editors as well. Neil Bowers (the man behind Geekcruises) has a
309 list of Mac editors that can handle Perl (
310 http://www.neilbowers.org/macperleditors.html ).
316 http://www.gnu.org/software/emacs/windows/ntemacs.html
320 http://www.microemacs.de/
324 http://www.xemacs.org/Download/index.html
328 http://space.mit.edu/~davis/jed/
332 or a vi clone such as
338 ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/
342 http://dickey.his.com/vile/vile.html
350 For vi lovers in general, Windows or elsewhere:
352 http://www.thomer.com/thomer/vi/vi.html
354 nvi ( http://www.bostic.com/vi/ , available from CPAN in src/misc/) is
355 yet another vi clone, unfortunately not available for Windows, but in
356 UNIX platforms you might be interested in trying it out, firstly because
357 strictly speaking it is not a vi clone, it is the real vi, or the new
358 incarnation of it, and secondly because you can embed Perl inside it
359 to use Perl as the scripting language. nvi is not alone in this,
360 though: at least also vim and vile offer an embedded Perl.
362 The following are Win32 multilanguage editor/IDESs that support Perl:
368 http://www.borland.com/codewright/
372 http://www.MultiEdit.com/
376 http://www.slickedit.com/
380 There is also a toyedit Text widget based editor written in Perl
381 that is distributed with the Tk module on CPAN. The ptkdb
382 ( http://world.std.com/~aep/ptkdb/ ) is a Perl/tk based debugger that
383 acts as a development environment of sorts. Perl Composer
384 ( http://perlcomposer.sourceforge.net/ ) is an IDE for Perl/Tk
387 In addition to an editor/IDE you might be interested in a more
388 powerful shell environment for Win32. Your options include
394 from the Cygwin package ( http://sources.redhat.com/cygwin/ )
398 from the MKS Toolkit ( http://www.mks.com/ ), or the Bourne shell of
399 the U/WIN environment ( http://www.research.att.com/sw/tools/uwin/ )
403 ftp://ftp.astron.com/pub/tcsh/ , see also
404 http://www.primate.wisc.edu/software/csh-tcsh-book/
408 ftp://ftp.blarg.net/users/amol/zsh/ , see also http://www.zsh.org/
412 MKS and U/WIN are commercial (U/WIN is free for educational and
413 research purposes), Cygwin is covered by the GNU Public License (but
414 that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all
415 contain (in addition to the shells) a comprehensive set of standard
416 UNIX toolkit utilities.
418 If you're transferring text files between Unix and Windows using FTP
419 be sure to transfer them in ASCII mode so the ends of lines are
420 appropriately converted.
422 On Mac OS the MacPerl Application comes with a simple 32k text editor
423 that behaves like a rudimentary IDE. In contrast to the MacPerl Application
424 the MPW Perl tool can make use of the MPW Shell itself as an editor (with
431 is a full Perl development environment with full debugger support
432 ( http://www.latenightsw.com ).
436 is an editor, written and extensible in Tcl, that nonetheless has
437 built in support for several popular markup and programming languages
438 including Perl and HTML ( http://www.his.com/~jguyer/Alpha/Alpha8.html ).
440 =item BBEdit and BBEdit Lite
442 are text editors for Mac OS that have a Perl sensitivity mode
443 ( http://web.barebones.com/ ).
448 Pepper and Pe are programming language sensitive text editors for Mac
449 OS X and BeOS respectively ( http://www.hekkelman.com/ ).
451 =head2 Where can I get Perl macros for vi?
453 For a complete version of Tom Christiansen's vi configuration file,
454 see http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz ,
455 the standard benchmark file for vi emulators. The file runs best with nvi,
456 the current version of vi out of Berkeley, which incidentally can be built
457 with an embedded Perl interpreter--see http://www.cpan.org/src/misc/ .
459 =head2 Where can I get perl-mode for emacs?
461 Since Emacs version 19 patchlevel 22 or so, there have been both a
462 perl-mode.el and support for the Perl debugger built in. These should
463 come with the standard Emacs 19 distribution.
465 In the Perl source directory, you'll find a directory called "emacs",
466 which contains a cperl-mode that color-codes keywords, provides
467 context-sensitive help, and other nifty things.
469 Note that the perl-mode of emacs will have fits with C<"main'foo">
470 (single quote), and mess up the indentation and highlighting. You
471 are probably using C<"main::foo"> in new Perl code anyway, so this
472 shouldn't be an issue.
474 =head2 How can I use curses with Perl?
476 The Curses module from CPAN provides a dynamically loadable object
477 module interface to a curses library. A small demo can be found at the
478 directory http://www.cpan.org/authors/Tom_Christiansen/scripts/rep.gz ;
479 this program repeats a command and updates the screen as needed, rendering
480 B<rep ps axu> similar to B<top>.
482 =head2 How can I use X or Tk with Perl?
484 Tk is a completely Perl-based, object-oriented interface to the Tk toolkit
485 that doesn't force you to use Tcl just to get at Tk. Sx is an interface
486 to the Athena Widget set. Both are available from CPAN. See the
487 directory http://www.cpan.org/modules/by-category/08_User_Interfaces/
489 Invaluable for Perl/Tk programming are the Perl/Tk FAQ at
490 http://phaseit.net/claird/comp.lang.perl.tk/ptkFAQ.html , the Perl/Tk Reference
492 http://www.cpan.org/authors/Stephen_O_Lidie/ , and the
494 http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html .
496 =head2 How can I make my Perl program run faster?
498 The best way to do this is to come up with a better algorithm. This
499 can often make a dramatic difference. Jon Bentley's book
500 I<Programming Pearls> (that's not a misspelling!) has some good tips
501 on optimization, too. Advice on benchmarking boils down to: benchmark
502 and profile to make sure you're optimizing the right part, look for
503 better algorithms instead of microtuning your code, and when all else
504 fails consider just buying faster hardware. You will probably want to
505 read the answer to the earlier question "How do I profile my Perl
506 programs?" if you haven't done so already.
508 A different approach is to autoload seldom-used Perl code. See the
509 AutoSplit and AutoLoader modules in the standard distribution for
510 that. Or you could locate the bottleneck and think about writing just
511 that part in C, the way we used to take bottlenecks in C code and
512 write them in assembler. Similar to rewriting in C, modules that have
513 critical sections can be written in C (for instance, the PDL module
516 If you're currently linking your perl executable to a shared
517 I<libc.so>, you can often gain a 10-25% performance benefit by
518 rebuilding it to link with a static libc.a instead. This will make a
519 bigger perl executable, but your Perl programs (and programmers) may
520 thank you for it. See the F<INSTALL> file in the source distribution
521 for more information.
523 The undump program was an ancient attempt to speed up Perl program by
524 storing the already-compiled form to disk. This is no longer a viable
525 option, as it only worked on a few architectures, and wasn't a good
528 =head2 How can I make my Perl program take less memory?
530 When it comes to time-space tradeoffs, Perl nearly always prefers to
531 throw memory at a problem. Scalars in Perl use more memory than
532 strings in C, arrays take more than that, and hashes use even more. While
533 there's still a lot to be done, recent releases have been addressing
534 these issues. For example, as of 5.004, duplicate hash keys are
535 shared amongst all hashes using them, so require no reallocation.
537 In some cases, using substr() or vec() to simulate arrays can be
538 highly beneficial. For example, an array of a thousand booleans will
539 take at least 20,000 bytes of space, but it can be turned into one
540 125-byte bit vector--a considerable memory savings. The standard
541 Tie::SubstrHash module can also help for certain types of data
542 structure. If you're working with specialist data structures
543 (matrices, for instance) modules that implement these in C may use
544 less memory than equivalent Perl modules.
546 Another thing to try is learning whether your Perl was compiled with
547 the system malloc or with Perl's builtin malloc. Whichever one it
548 is, try using the other one and see whether this makes a difference.
549 Information about malloc is in the F<INSTALL> file in the source
550 distribution. You can find out whether you are using perl's malloc by
551 typing C<perl -V:usemymalloc>.
553 Of course, the best way to save memory is to not do anything to waste
554 it in the first place. Good programming practices can go a long way
561 Don't read an entire file into memory if you can process it line
562 by line. Or more concretely, use a loop like this:
581 When the files you're processing are small, it doesn't much matter which
582 way you do it, but it makes a huge difference when they start getting
585 =item * Use map and grep selectively
587 Remember that both map and grep expect a LIST argument, so doing this:
589 @wanted = grep {/pattern/} <FILE>;
591 will cause the entire file to be slurped. For large files, it's better
595 push(@wanted, $_) if /pattern/;
598 =item * Avoid unnecessary quotes and stringification
600 Don't quote large strings unless absolutely necessary:
602 my $copy = "$large_string";
604 makes 2 copies of $large_string (one for $copy and another for the
607 my $copy = $large_string;
611 Ditto for stringifying large arrays:
618 is much more memory-efficient than either
620 print join "\n", @big_array;
630 =item * Pass by reference
632 Pass arrays and hashes by reference, not by value. For one thing, it's
633 the only way to pass multiple lists or hashes (or both) in a single
634 call/return. It also avoids creating a copy of all the contents. This
635 requires some judgment, however, because any changes will be propagated
636 back to the original data. If you really want to mangle (er, modify) a
637 copy, you'll have to sacrifice the memory needed to make one.
639 =item * Tie large variables to disk.
641 For "big" data stores (i.e. ones that exceed available memory) consider
642 using one of the DB modules to store it on disk instead of in RAM. This
643 will incur a penalty in access time, but that's probably better than
644 causing your hard disk to thrash due to massive swapping.
648 =head2 Is it safe to return a reference to local or lexical data?
650 Yes. Perl's garbage collection system takes care of this so
651 everything works out right.
659 push @many, makeone();
662 print $many[4][5], "\n";
666 =head2 How can I free an array or hash so my program shrinks?
668 (contributed by Michael Carman)
670 You usually can't. Memory allocated to lexicals (i.e. my() variables)
671 cannot be reclaimed or reused even if they go out of scope. It is
672 reserved in case the variables come back into scope. Memory allocated
673 to global variables can be reused (within your program) by using
674 undef()ing and/or delete().
676 On most operating systems, memory allocated to a program can never be
677 returned to the system. That's why long-running programs sometimes re-
678 exec themselves. Some operating systems (notably, systems that use
679 mmap(2) for allocating large chunks of memory) can reclaim memory that
680 is no longer used, but on such systems, perl must be configured and
681 compiled to use the OS's malloc, not perl's.
683 In general, memory allocation and de-allocation isn't something you can
684 or should be worrying about much in Perl.
686 See also "How can I make my Perl program take less memory?"
688 =head2 How can I make my CGI script more efficient?
690 Beyond the normal measures described to make general Perl programs
691 faster or smaller, a CGI program has additional issues. It may be run
692 several times per second. Given that each time it runs it will need
693 to be re-compiled and will often allocate a megabyte or more of system
694 memory, this can be a killer. Compiling into C B<isn't going to help
695 you> because the process start-up overhead is where the bottleneck is.
697 There are two popular ways to avoid this overhead. One solution
698 involves running the Apache HTTP server (available from
699 http://www.apache.org/ ) with either of the mod_perl or mod_fastcgi
702 With mod_perl and the Apache::Registry module (distributed with
703 mod_perl), httpd will run with an embedded Perl interpreter which
704 pre-compiles your script and then executes it within the same address
705 space without forking. The Apache extension also gives Perl access to
706 the internal server API, so modules written in Perl can do just about
707 anything a module written in C can. For more on mod_perl, see
708 http://perl.apache.org/
710 With the FCGI module (from CPAN) and the mod_fastcgi
711 module (available from http://www.fastcgi.com/ ) each of your Perl
712 programs becomes a permanent CGI daemon process.
714 Both of these solutions can have far-reaching effects on your system
715 and on the way you write your CGI programs, so investigate them with
718 See http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
720 =head2 How can I hide the source for my Perl program?
722 Delete it. :-) Seriously, there are a number of (mostly
723 unsatisfactory) solutions with varying levels of "security".
725 First of all, however, you I<can't> take away read permission, because
726 the source code has to be readable in order to be compiled and
727 interpreted. (That doesn't mean that a CGI script's source is
728 readable by people on the web, though--only by people with access to
729 the filesystem.) So you have to leave the permissions at the socially
732 Some people regard this as a security problem. If your program does
733 insecure things and relies on people not knowing how to exploit those
734 insecurities, it is not secure. It is often possible for someone to
735 determine the insecure things and exploit them without viewing the
736 source. Security through obscurity, the name for hiding your bugs
737 instead of fixing them, is little security indeed.
739 You can try using encryption via source filters (Starting from Perl
740 5.8 the Filter::Simple and Filter::Util::Call modules are included in
741 the standard distribution), but any decent programmer will be able to
742 decrypt it. You can try using the byte code compiler and interpreter
743 described below, but the curious might still be able to de-compile it.
744 You can try using the native-code compiler described below, but
745 crackers might be able to disassemble it. These pose varying degrees
746 of difficulty to people wanting to get at your code, but none can
747 definitively conceal it (true of every language, not just Perl).
749 It is very easy to recover the source of Perl programs. You simply
750 feed the program to the perl interpreter and use the modules in
751 the B:: hierarchy. The B::Deparse module should be able to
752 defeat most attempts to hide source. Again, this is not
755 If you're concerned about people profiting from your code, then the
756 bottom line is that nothing but a restrictive license will give you
757 legal security. License your software and pepper it with threatening
758 statements like "This is unpublished proprietary software of XYZ Corp.
759 Your access to it does not give you permission to use it blah blah
760 blah." We are not lawyers, of course, so you should see a lawyer if
761 you want to be sure your license's wording will stand up in court.
763 =head2 How can I compile my Perl program into byte code or C?
765 (contributed by brian d foy)
767 In general, you can't do this. There are some things that may work
768 for your situation though. People usually ask this question
769 because they want to distribute their works without giving away
770 the source code, and most solutions trade disk space for convenience.
771 You probably won't see much of a speed increase either, since most
772 solutions simply bundle a Perl interpreter in the final product
773 (but see L<How can I make my Perl program run faster?>).
775 The Perl Archive Toolkit (http://par.perl.org/index.cgi) is
776 Perl's analog to Java's JAR. It's freely available and on
777 CPAN (http://search.cpan.org/dist/PAR/).
779 The B::* namespace, often called "the Perl compiler", but is really a
780 way for Perl programs to peek at its innards rather than create
781 pre-compiled versions of your program. However. the B::Bytecode
782 module can turn your script into a bytecode format that could be
783 loaded later by the ByteLoader module and executed as a regular Perl
786 There are also some commercial products that may work for
787 you, although you have to buy a license for them.
790 (http://www.activestate.com/Products/Perl_Dev_Kit/) from
791 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
795 command line program for converting perl scripts to
796 executable files. It targets both Windows and unix
800 =head2 How can I compile Perl into Java?
802 You can also integrate Java and Perl with the
803 Perl Resource Kit from O'Reilly Media. See
804 http://www.oreilly.com/catalog/prkunix/ .
806 Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in
807 development, allows Perl code to be called from Java. See jpl/README
808 in the Perl source tree.
810 =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
814 extproc perl -S -your_switches
816 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
817 "extproc" handling). For DOS one should first invent a corresponding
818 batch file and codify it in C<ALTERNATE_SHEBANG> (see the
819 F<dosish.h> file in the source distribution for more information).
821 The Win95/NT installation, when using the ActiveState port of Perl,
822 will modify the Registry to associate the C<.pl> extension with the
823 perl interpreter. If you install another port, perhaps even building
824 your own Win95/NT Perl from the standard sources by using a Windows port
825 of gcc (e.g., with cygwin or mingw32), then you'll have to modify
826 the Registry yourself. In addition to associating C<.pl> with the
827 interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them
828 run the program C<install-linux.pl> merely by typing C<install-linux>.
830 Under "Classic" MacOS, a perl program will have the appropriate Creator and
831 Type, so that double-clicking them will invoke the MacPerl application.
832 Under Mac OS X, clickable apps can be made from any C<#!> script using Wil
833 Sanchez' DropScript utility: http://www.wsanchez.net/software/ .
835 I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
836 throw the perl interpreter into your cgi-bin directory, in order to
837 get your programs working for a web server. This is an EXTREMELY big
838 security risk. Take the time to figure out how to do it correctly.
840 =head2 Can I write useful Perl programs on the command line?
842 Yes. Read L<perlrun> for more information. Some examples follow.
843 (These assume standard Unix shell quoting rules.)
845 # sum first and last fields
846 perl -lane 'print $F[0] + $F[-1]' *
848 # identify text files
849 perl -le 'for(@ARGV) {print if -f && -T _}' *
851 # remove (most) comments from C program
852 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
854 # make file a month younger than today, defeating reaper daemons
855 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
857 # find first unused uid
858 perl -le '$i++ while getpwuid($i); print $i'
860 # display reasonable manpath
861 echo $PATH | perl -nl -072 -e '
862 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
864 OK, the last one was actually an Obfuscated Perl Contest entry. :-)
866 =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system?
868 The problem is usually that the command interpreters on those systems
869 have rather different ideas about quoting than the Unix shells under
870 which the one-liners were created. On some systems, you may have to
871 change single-quotes to double ones, which you must I<NOT> do on Unix
872 or Plan9 systems. You might also have to change a single % to a %%.
877 perl -e 'print "Hello world\n"'
880 perl -e "print \"Hello world\n\""
883 print "Hello world\n"
884 (then Run "Myscript" or Shift-Command-R)
887 perl -e 'print "Hello world\n"'
890 perl -e "print ""Hello world\n"""
892 The problem is that none of these examples are reliable: they depend on the
893 command interpreter. Under Unix, the first two often work. Under DOS,
894 it's entirely possible that neither works. If 4DOS was the command shell,
895 you'd probably have better luck like this:
897 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
899 Under the Mac, it depends which environment you are using. The MacPerl
900 shell, or MPW, is much like Unix shells in its support for several
901 quoting variants, except that it makes free use of the Mac's non-ASCII
902 characters as control characters.
904 Using qq(), q(), and qx(), instead of "double quotes", 'single
905 quotes', and `backticks`, may make one-liners easier to write.
907 There is no general solution to all of this. It is a mess.
909 [Some of this answer was contributed by Kenneth Albanowski.]
911 =head2 Where can I learn about CGI or Web programming in Perl?
913 For modules, get the CGI or LWP modules from CPAN. For textbooks,
914 see the two especially dedicated to web stuff in the question on
915 books. For problems and questions related to the web, like "Why
916 do I get 500 Errors" or "Why doesn't it run from the browser right
917 when it runs fine on the command line", see the troubleshooting
918 guides and references in L<perlfaq9> or in the CGI MetaFAQ:
920 http://www.perl.org/CGI_MetaFAQ.html
922 =head2 Where can I learn about object-oriented Perl programming?
924 A good place to start is L<perltoot>, and you can use L<perlobj>,
925 L<perlboot>, L<perltoot>, L<perltooc>, and L<perlbot> for reference.
926 (If you are using really old Perl, you may not have all of these,
927 try http://www.perldoc.com/ , but consider upgrading your perl.)
929 A good book on OO on Perl is the "Object-Oriented Perl"
930 by Damian Conway from Manning Publications,
931 http://www.manning.com/Conway/index.html
933 =head2 Where can I learn about linking C with Perl?
935 If you want to call C from Perl, start with L<perlxstut>,
936 moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to
937 call Perl from C, then read L<perlembed>, L<perlcall>, and
938 L<perlguts>. Don't forget that you can learn a lot from looking at
939 how the authors of existing extension modules wrote their code and
940 solved their problems.
942 You might not need all the power of XS. The Inline::C module lets
943 you put C code directly in your Perl source. It handles all the
944 magic to make it work. You still have to learn at least some of
945 the perl API but you won't have to deal with the complexity of the
948 =head2 I've read perlembed, perlguts, etc., but I can't embed perl in my C program; what am I doing wrong?
950 Download the ExtUtils::Embed kit from CPAN and run `make test'. If
951 the tests pass, read the pods again and again and again. If they
952 fail, see L<perlbug> and send a bug report with the output of
953 C<make test TEST_VERBOSE=1> along with C<perl -V>.
955 =head2 When I tried to run my script, I got this message. What does it mean?
957 A complete list of Perl's error messages and warnings with explanatory
958 text can be found in L<perldiag>. You can also use the splain program
959 (distributed with Perl) to explain the error messages:
961 perl program 2>diag.out
962 splain [-v] [-p] diag.out
964 or change your program to explain the messages for you:
970 use diagnostics -verbose;
972 =head2 What's MakeMaker?
974 This module (part of the standard Perl distribution) is designed to
975 write a Makefile for an extension module from a Makefile.PL. For more
976 information, see L<ExtUtils::MakeMaker>.
978 =head1 AUTHOR AND COPYRIGHT
980 Copyright (c) 1997-2005 Tom Christiansen, Nathan Torkington, and
981 other authors as noted. All rights reserved.
983 This documentation is free; you can redistribute it and/or modify it
984 under the same terms as Perl itself.
986 Irrespective of its distribution, all code examples here are in the public
987 domain. You are permitted and encouraged to use this code and any
988 derivatives thereof in your own programs for fun or for profit as you
989 see fit. A simple comment in the code giving credit to the FAQ would
990 be courteous but is not required.