3 perlfaq3 - Programming Tools ($Revision: 1.46 $, $Date: 2005/02/13 02:36:09 $)
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 Recent versions of ctags do much more than older versions did.
206 EXUBERANT CTAGS is available from http://ctags.sourceforge.net/
207 and does a good job of making tags files for perl code.
209 There is also a simple one at
210 http://www.cpan.org/authors/id/TOMC/scripts/ptags.gz which may do
211 the trick. It can be easy to hack this into what you want.
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 The Eclipse Perl Integration Project integrates Perl
229 editing/debugging with Eclipse.
231 The website for the project is http://e-p-i-c.sf.net/
235 ActiveState's cross-platform (as of October 2004, that's Windows, Linux,
236 and Solaris), multi-language IDE has Perl support, including a regular expression
237 debugger and remote debugging
238 ( http://www.ActiveState.com/Products/Komodo/ ).
242 ( http://open-perl-ide.sourceforge.net/ )
243 Open Perl IDE is an integrated development environment for writing
244 and debugging Perl scripts with ActiveState's ActivePerl distribution
245 under Windows 95/98/NT/2000.
249 ( http://www.optiperl.com/ ) is a Windows IDE with simulated CGI
250 environment, including debugger and syntax highlighting editor.
254 ( http://www.solutionsoft.com/perl.htm ) is an integrated development
255 environment for Windows that supports Perl development.
259 ( http://helpconsulting.net/visiperl/ )
260 From Help Consulting, for Windows.
264 ( http://www.activestate.com/Products/Visual_Perl/ )
265 Visual Perl is a Visual Studio.NET plug-in from ActiveState.
270 For editors: if you're on Unix you probably have vi or a vi clone already,
271 and possibly an emacs too, so you may not need to download anything.
272 In any emacs the cperl-mode (M-x cperl-mode) gives you perhaps the
273 best available Perl editing mode in any editor.
275 If you are using Windows, you can use any editor that lets
276 you work with plain text, such as NotePad or WordPad. Word
277 processors, such as Microsoft Word or WordPerfect, typically
278 do not work since they insert all sorts of behind-the-scenes
279 information, although some allow you to save files as "Text
280 Only". You can also download text editors designed
281 specifically for programming, such as Textpad
282 ( http://www.textpad.com/ ) and UltraEdit
283 ( http://www.ultraedit.com/ ), among others.
285 If you are using MacOS, the same concerns apply. MacPerl
286 (for Classic environments) comes with a simple editor.
287 Popular external editors are BBEdit ( http://www.bbedit.com/ )
288 or Alpha ( http://www.his.com/~jguyer/Alpha/Alpha8.html ). MacOS X users can
289 use Unix editors as well.
295 http://www.gnu.org/software/emacs/windows/ntemacs.html
299 http://www.microemacs.de/
303 http://www.xemacs.org/Download/index.html
307 http://space.mit.edu/~davis/jed/
311 or a vi clone such as
317 ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/
321 http://dickey.his.com/vile/vile.html
329 For vi lovers in general, Windows or elsewhere:
331 http://www.thomer.com/thomer/vi/vi.html
333 nvi ( http://www.bostic.com/vi/ , available from CPAN in src/misc/) is
334 yet another vi clone, unfortunately not available for Windows, but in
335 UNIX platforms you might be interested in trying it out, firstly because
336 strictly speaking it is not a vi clone, it is the real vi, or the new
337 incarnation of it, and secondly because you can embed Perl inside it
338 to use Perl as the scripting language. nvi is not alone in this,
339 though: at least also vim and vile offer an embedded Perl.
341 The following are Win32 multilanguage editor/IDESs that support Perl:
347 http://www.borland.com/codewright/
351 http://www.MultiEdit.com/
355 http://www.slickedit.com/
359 There is also a toyedit Text widget based editor written in Perl
360 that is distributed with the Tk module on CPAN. The ptkdb
361 ( http://world.std.com/~aep/ptkdb/ ) is a Perl/tk based debugger that
362 acts as a development environment of sorts. Perl Composer
363 ( http://perlcomposer.sourceforge.net/ ) is an IDE for Perl/Tk
366 In addition to an editor/IDE you might be interested in a more
367 powerful shell environment for Win32. Your options include
373 from the Cygwin package ( http://sources.redhat.com/cygwin/ )
377 from the MKS Toolkit ( http://www.mks.com/ ), or the Bourne shell of
378 the U/WIN environment ( http://www.research.att.com/sw/tools/uwin/ )
382 ftp://ftp.astron.com/pub/tcsh/ , see also
383 http://www.primate.wisc.edu/software/csh-tcsh-book/
387 ftp://ftp.blarg.net/users/amol/zsh/ , see also http://www.zsh.org/
391 MKS and U/WIN are commercial (U/WIN is free for educational and
392 research purposes), Cygwin is covered by the GNU Public License (but
393 that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all
394 contain (in addition to the shells) a comprehensive set of standard
395 UNIX toolkit utilities.
397 If you're transferring text files between Unix and Windows using FTP
398 be sure to transfer them in ASCII mode so the ends of lines are
399 appropriately converted.
401 On Mac OS the MacPerl Application comes with a simple 32k text editor
402 that behaves like a rudimentary IDE. In contrast to the MacPerl Application
403 the MPW Perl tool can make use of the MPW Shell itself as an editor (with
410 is a full Perl development enivornment with full debugger support
411 ( http://www.latenightsw.com ).
415 is an editor, written and extensible in Tcl, that nonetheless has
416 built in support for several popular markup and programming languages
417 including Perl and HTML ( http://www.his.com/~jguyer/Alpha/Alpha8.html ).
419 =item BBEdit and BBEdit Lite
421 are text editors for Mac OS that have a Perl sensitivity mode
422 ( http://web.barebones.com/ ).
427 Pepper and Pe are programming language sensitive text editors for Mac
428 OS X and BeOS respectively ( http://www.hekkelman.com/ ).
430 =head2 Where can I get Perl macros for vi?
432 For a complete version of Tom Christiansen's vi configuration file,
433 see http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz ,
434 the standard benchmark file for vi emulators. The file runs best with nvi,
435 the current version of vi out of Berkeley, which incidentally can be built
436 with an embedded Perl interpreter--see http://www.cpan.org/src/misc/ .
438 =head2 Where can I get perl-mode for emacs?
440 Since Emacs version 19 patchlevel 22 or so, there have been both a
441 perl-mode.el and support for the Perl debugger built in. These should
442 come with the standard Emacs 19 distribution.
444 In the Perl source directory, you'll find a directory called "emacs",
445 which contains a cperl-mode that color-codes keywords, provides
446 context-sensitive help, and other nifty things.
448 Note that the perl-mode of emacs will have fits with C<"main'foo">
449 (single quote), and mess up the indentation and highlighting. You
450 are probably using C<"main::foo"> in new Perl code anyway, so this
451 shouldn't be an issue.
453 =head2 How can I use curses with Perl?
455 The Curses module from CPAN provides a dynamically loadable object
456 module interface to a curses library. A small demo can be found at the
457 directory http://www.cpan.org/authors/Tom_Christiansen/scripts/rep.gz ;
458 this program repeats a command and updates the screen as needed, rendering
459 B<rep ps axu> similar to B<top>.
461 =head2 How can I use X or Tk with Perl?
463 Tk is a completely Perl-based, object-oriented interface to the Tk toolkit
464 that doesn't force you to use Tcl just to get at Tk. Sx is an interface
465 to the Athena Widget set. Both are available from CPAN. See the
466 directory http://www.cpan.org/modules/by-category/08_User_Interfaces/
468 Invaluable for Perl/Tk programming are the Perl/Tk FAQ at
469 http://phaseit.net/claird/comp.lang.perl.tk/ptkFAQ.html , the Perl/Tk Reference
471 http://www.cpan.org/authors/Stephen_O_Lidie/ , and the
473 http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html .
475 =head2 How can I generate simple menus without using CGI or Tk?
477 The http://www.cpan.org/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
478 module, which is curses-based, can help with this.
480 =head2 How can I make my Perl program run faster?
482 The best way to do this is to come up with a better algorithm. This
483 can often make a dramatic difference. Jon Bentley's book
484 I<Programming Pearls> (that's not a misspelling!) has some good tips
485 on optimization, too. Advice on benchmarking boils down to: benchmark
486 and profile to make sure you're optimizing the right part, look for
487 better algorithms instead of microtuning your code, and when all else
488 fails consider just buying faster hardware. You will probably want to
489 read the answer to the earlier question ``How do I profile my Perl
490 programs?'' if you haven't done so already.
492 A different approach is to autoload seldom-used Perl code. See the
493 AutoSplit and AutoLoader modules in the standard distribution for
494 that. Or you could locate the bottleneck and think about writing just
495 that part in C, the way we used to take bottlenecks in C code and
496 write them in assembler. Similar to rewriting in C, modules that have
497 critical sections can be written in C (for instance, the PDL module
500 If you're currently linking your perl executable to a shared
501 I<libc.so>, you can often gain a 10-25% performance benefit by
502 rebuilding it to link with a static libc.a instead. This will make a
503 bigger perl executable, but your Perl programs (and programmers) may
504 thank you for it. See the F<INSTALL> file in the source distribution
505 for more information.
507 The undump program was an ancient attempt to speed up Perl program by
508 storing the already-compiled form to disk. This is no longer a viable
509 option, as it only worked on a few architectures, and wasn't a good
512 =head2 How can I make my Perl program take less memory?
514 When it comes to time-space tradeoffs, Perl nearly always prefers to
515 throw memory at a problem. Scalars in Perl use more memory than
516 strings in C, arrays take more than that, and hashes use even more. While
517 there's still a lot to be done, recent releases have been addressing
518 these issues. For example, as of 5.004, duplicate hash keys are
519 shared amongst all hashes using them, so require no reallocation.
521 In some cases, using substr() or vec() to simulate arrays can be
522 highly beneficial. For example, an array of a thousand booleans will
523 take at least 20,000 bytes of space, but it can be turned into one
524 125-byte bit vector--a considerable memory savings. The standard
525 Tie::SubstrHash module can also help for certain types of data
526 structure. If you're working with specialist data structures
527 (matrices, for instance) modules that implement these in C may use
528 less memory than equivalent Perl modules.
530 Another thing to try is learning whether your Perl was compiled with
531 the system malloc or with Perl's builtin malloc. Whichever one it
532 is, try using the other one and see whether this makes a difference.
533 Information about malloc is in the F<INSTALL> file in the source
534 distribution. You can find out whether you are using perl's malloc by
535 typing C<perl -V:usemymalloc>.
537 Of course, the best way to save memory is to not do anything to waste
538 it in the first place. Good programming practices can go a long way
545 Don't read an entire file into memory if you can process it line
546 by line. Or more concretely, use a loop like this:
565 When the files you're processing are small, it doesn't much matter which
566 way you do it, but it makes a huge difference when they start getting
569 =item * Use map and grep selectively
571 Remember that both map and grep expect a LIST argument, so doing this:
573 @wanted = grep {/pattern/} <FILE>;
575 will cause the entire file to be slurped. For large files, it's better
579 push(@wanted, $_) if /pattern/;
582 =item * Avoid unnecessary quotes and stringification
584 Don't quote large strings unless absolutely necessary:
586 my $copy = "$large_string";
588 makes 2 copies of $large_string (one for $copy and another for the
591 my $copy = $large_string;
595 Ditto for stringifying large arrays:
602 is much more memory-efficient than either
604 print join "\n", @big_array;
614 =item * Pass by reference
616 Pass arrays and hashes by reference, not by value. For one thing, it's
617 the only way to pass multiple lists or hashes (or both) in a single
618 call/return. It also avoids creating a copy of all the contents. This
619 requires some judgment, however, because any changes will be propagated
620 back to the original data. If you really want to mangle (er, modify) a
621 copy, you'll have to sacrifice the memory needed to make one.
623 =item * Tie large variables to disk.
625 For "big" data stores (i.e. ones that exceed available memory) consider
626 using one of the DB modules to store it on disk instead of in RAM. This
627 will incur a penalty in access time, but that's probably better than
628 causing your hard disk to thrash due to massive swapping.
632 =head2 Is it safe to return a reference to local or lexical data?
634 Yes. Perl's garbage collection system takes care of this so
635 everything works out right.
643 push @many, makeone();
646 print $many[4][5], "\n";
650 =head2 How can I free an array or hash so my program shrinks?
652 (contributed by Michael Carman)
654 You usually can't. Memory allocated to lexicals (i.e. my() variables)
655 cannot be reclaimed or reused even if they go out of scope. It is
656 reserved in case the variables come back into scope. Memory allocated
657 to global variables can be reused (within your program) by using
658 undef()ing and/or delete().
660 On most operating systems, memory allocated to a program can never be
661 returned to the system. That's why long-running programs sometimes re-
662 exec themselves. Some operating systems (notably, systems that use
663 mmap(2) for allocating large chunks of memory) can reclaim memory that
664 is no longer used, but on such systems, perl must be configured and
665 compiled to use the OS's malloc, not perl's.
667 In general, memory allocation and de-allocation isn't something you can
668 or should be worrying about much in Perl.
670 See also "How can I make my Perl program take less memory?"
672 =head2 How can I make my CGI script more efficient?
674 Beyond the normal measures described to make general Perl programs
675 faster or smaller, a CGI program has additional issues. It may be run
676 several times per second. Given that each time it runs it will need
677 to be re-compiled and will often allocate a megabyte or more of system
678 memory, this can be a killer. Compiling into C B<isn't going to help
679 you> because the process start-up overhead is where the bottleneck is.
681 There are two popular ways to avoid this overhead. One solution
682 involves running the Apache HTTP server (available from
683 http://www.apache.org/ ) with either of the mod_perl or mod_fastcgi
686 With mod_perl and the Apache::Registry module (distributed with
687 mod_perl), httpd will run with an embedded Perl interpreter which
688 pre-compiles your script and then executes it within the same address
689 space without forking. The Apache extension also gives Perl access to
690 the internal server API, so modules written in Perl can do just about
691 anything a module written in C can. For more on mod_perl, see
692 http://perl.apache.org/
694 With the FCGI module (from CPAN) and the mod_fastcgi
695 module (available from http://www.fastcgi.com/ ) each of your Perl
696 programs becomes a permanent CGI daemon process.
698 Both of these solutions can have far-reaching effects on your system
699 and on the way you write your CGI programs, so investigate them with
702 See http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
704 A non-free, commercial product, ``The Velocity Engine for Perl'',
705 (http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ )
706 might also be worth looking at. It will allow you to increase the
707 performance of your Perl programs, running programs up to 25 times
708 faster than normal CGI Perl when running in persistent Perl mode or 4
709 to 5 times faster without any modification to your existing CGI
710 programs. Fully functional evaluation copies are available from the
713 =head2 How can I hide the source for my Perl program?
715 Delete it. :-) Seriously, there are a number of (mostly
716 unsatisfactory) solutions with varying levels of ``security''.
718 First of all, however, you I<can't> take away read permission, because
719 the source code has to be readable in order to be compiled and
720 interpreted. (That doesn't mean that a CGI script's source is
721 readable by people on the web, though--only by people with access to
722 the filesystem.) So you have to leave the permissions at the socially
725 Some people regard this as a security problem. If your program does
726 insecure things and relies on people not knowing how to exploit those
727 insecurities, it is not secure. It is often possible for someone to
728 determine the insecure things and exploit them without viewing the
729 source. Security through obscurity, the name for hiding your bugs
730 instead of fixing them, is little security indeed.
732 You can try using encryption via source filters (Starting from Perl
733 5.8 the Filter::Simple and Filter::Util::Call modules are included in
734 the standard distribution), but any decent programmer will be able to
735 decrypt it. You can try using the byte code compiler and interpreter
736 described below, but the curious might still be able to de-compile it.
737 You can try using the native-code compiler described below, but
738 crackers might be able to disassemble it. These pose varying degrees
739 of difficulty to people wanting to get at your code, but none can
740 definitively conceal it (true of every language, not just Perl).
742 It is very easy to recover the source of Perl programs. You simply
743 feed the program to the perl interpreter and use the modules in
744 the B:: hierarchy. The B::Deparse module should be able to
745 defeat most attempts to hide source. Again, this is not
748 If you're concerned about people profiting from your code, then the
749 bottom line is that nothing but a restrictive license will give you
750 legal security. License your software and pepper it with threatening
751 statements like ``This is unpublished proprietary software of XYZ Corp.
752 Your access to it does not give you permission to use it blah blah
753 blah.'' We are not lawyers, of course, so you should see a lawyer if
754 you want to be sure your license's wording will stand up in court.
756 =head2 How can I compile my Perl program into byte code or C?
758 (contributed by brian d foy)
760 In general, you can't do this. There are some things that may work
761 for your situation though. People usually ask this question
762 because they want to distribute their works without giving away
763 the source code, and most solutions trade disk space for convenience.
764 You probably won't see much of a speed increase either, since most
765 solutions simply bundle a Perl interpreter in the final product
766 (but see L<How can I make my Perl program run faster?>).
768 The Perl Archive Toolkit (http://par.perl.org/index.cgi) is
769 Perl's analog to Java's JAR. It's freely available and on
770 CPAN (http://search.cpan.org/dist/PAR/).
772 The B::* namespace, often called "the Perl compiler", but is really a
773 way for Perl programs to peek at its innards rather than create
774 pre-compiled versions of your program. However. the B::Bytecode
775 module can turn your script into a bytecode format that could be
776 loaded later by the ByteLoader module and executed as a regular Perl
779 There are also some commercial products that may work for
780 you, although you have to buy a license for them.
783 (http://www.activestate.com/Products/Perl_Dev_Kit/) from
784 ActiveState can "Turn your Perl programs into ready-to-run
785 executables for HP-UX, Linux, Solaris and Windows."
787 Perl2Exe (http://www.indigostar.com/perl2exe.htm) is a
788 command line program for converting perl scripts to
789 executable files. It targets both Windows and unix
793 =head2 How can I compile Perl into Java?
795 You can also integrate Java and Perl with the
796 Perl Resource Kit from O'Reilly Media. See
797 http://www.oreilly.com/catalog/prkunix/ .
799 Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in
800 development, allows Perl code to be called from Java. See jpl/README
801 in the Perl source tree.
803 =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
807 extproc perl -S -your_switches
809 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
810 `extproc' handling). For DOS one should first invent a corresponding
811 batch file and codify it in C<ALTERNATE_SHEBANG> (see the
812 F<dosish.h> file in the source distribution for more information).
814 The Win95/NT installation, when using the ActiveState port of Perl,
815 will modify the Registry to associate the C<.pl> extension with the
816 perl interpreter. If you install another port, perhaps even building
817 your own Win95/NT Perl from the standard sources by using a Windows port
818 of gcc (e.g., with cygwin or mingw32), then you'll have to modify
819 the Registry yourself. In addition to associating C<.pl> with the
820 interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them
821 run the program C<install-linux.pl> merely by typing C<install-linux>.
823 Under "Classic" MacOS, a perl program will have the appropriate Creator and
824 Type, so that double-clicking them will invoke the MacPerl application.
825 Under Mac OS X, clickable apps can be made from any C<#!> script using Wil
826 Sanchez' DropScript utility: http://www.wsanchez.net/software/ .
828 I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
829 throw the perl interpreter into your cgi-bin directory, in order to
830 get your programs working for a web server. This is an EXTREMELY big
831 security risk. Take the time to figure out how to do it correctly.
833 =head2 Can I write useful Perl programs on the command line?
835 Yes. Read L<perlrun> for more information. Some examples follow.
836 (These assume standard Unix shell quoting rules.)
838 # sum first and last fields
839 perl -lane 'print $F[0] + $F[-1]' *
841 # identify text files
842 perl -le 'for(@ARGV) {print if -f && -T _}' *
844 # remove (most) comments from C program
845 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
847 # make file a month younger than today, defeating reaper daemons
848 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
850 # find first unused uid
851 perl -le '$i++ while getpwuid($i); print $i'
853 # display reasonable manpath
854 echo $PATH | perl -nl -072 -e '
855 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
857 OK, the last one was actually an Obfuscated Perl Contest entry. :-)
859 =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system?
861 The problem is usually that the command interpreters on those systems
862 have rather different ideas about quoting than the Unix shells under
863 which the one-liners were created. On some systems, you may have to
864 change single-quotes to double ones, which you must I<NOT> do on Unix
865 or Plan9 systems. You might also have to change a single % to a %%.
870 perl -e 'print "Hello world\n"'
873 perl -e "print \"Hello world\n\""
876 print "Hello world\n"
877 (then Run "Myscript" or Shift-Command-R)
880 perl -e 'print "Hello world\n"'
883 perl -e "print ""Hello world\n"""
885 The problem is that none of these examples are reliable: they depend on the
886 command interpreter. Under Unix, the first two often work. Under DOS,
887 it's entirely possible that neither works. If 4DOS was the command shell,
888 you'd probably have better luck like this:
890 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
892 Under the Mac, it depends which environment you are using. The MacPerl
893 shell, or MPW, is much like Unix shells in its support for several
894 quoting variants, except that it makes free use of the Mac's non-ASCII
895 characters as control characters.
897 Using qq(), q(), and qx(), instead of "double quotes", 'single
898 quotes', and `backticks`, may make one-liners easier to write.
900 There is no general solution to all of this. It is a mess.
902 [Some of this answer was contributed by Kenneth Albanowski.]
904 =head2 Where can I learn about CGI or Web programming in Perl?
906 For modules, get the CGI or LWP modules from CPAN. For textbooks,
907 see the two especially dedicated to web stuff in the question on
908 books. For problems and questions related to the web, like ``Why
909 do I get 500 Errors'' or ``Why doesn't it run from the browser right
910 when it runs fine on the command line'', see the troubleshooting
911 guides and references in L<perlfaq9> or in the CGI MetaFAQ:
913 http://www.perl.org/CGI_MetaFAQ.html
915 =head2 Where can I learn about object-oriented Perl programming?
917 A good place to start is L<perltoot>, and you can use L<perlobj>,
918 L<perlboot>, L<perltoot>, L<perltooc>, and L<perlbot> for reference.
919 (If you are using really old Perl, you may not have all of these,
920 try http://www.perldoc.com/ , but consider upgrading your perl.)
922 A good book on OO on Perl is the "Object-Oriented Perl"
923 by Damian Conway from Manning Publications,
924 http://www.manning.com/Conway/index.html
926 =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp]
928 If you want to call C from Perl, start with L<perlxstut>,
929 moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to
930 call Perl from C, then read L<perlembed>, L<perlcall>, and
931 L<perlguts>. Don't forget that you can learn a lot from looking at
932 how the authors of existing extension modules wrote their code and
933 solved their problems.
935 =head2 I've read perlembed, perlguts, etc., but I can't embed perl in my C program; what am I doing wrong?
937 Download the ExtUtils::Embed kit from CPAN and run `make test'. If
938 the tests pass, read the pods again and again and again. If they
939 fail, see L<perlbug> and send a bug report with the output of
940 C<make test TEST_VERBOSE=1> along with C<perl -V>.
942 =head2 When I tried to run my script, I got this message. What does it mean?
944 A complete list of Perl's error messages and warnings with explanatory
945 text can be found in L<perldiag>. You can also use the splain program
946 (distributed with Perl) to explain the error messages:
948 perl program 2>diag.out
949 splain [-v] [-p] diag.out
951 or change your program to explain the messages for you:
957 use diagnostics -verbose;
959 =head2 What's MakeMaker?
961 This module (part of the standard Perl distribution) is designed to
962 write a Makefile for an extension module from a Makefile.PL. For more
963 information, see L<ExtUtils::MakeMaker>.
965 =head1 AUTHOR AND COPYRIGHT
967 Copyright (c) 1997-2005 Tom Christiansen, Nathan Torkington, and
968 other authors as noted. All rights reserved.
970 This documentation is free; you can redistribute it and/or modify it
971 under the same terms as Perl itself.
973 Irrespective of its distribution, all code examples here are in the public
974 domain. You are permitted and encouraged to use this code and any
975 derivatives thereof in your own programs for fun or for profit as you
976 see fit. A simple comment in the code giving credit to the FAQ would
977 be courteous but is not required.