3 perlfaq3 - Programming Tools ($Revision: 1.33 $, $Date: 2003/01/31 17:34:56 $)
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 The Shell.pm module (distributed with Perl) makes Perl try commands
53 which aren't part of the Perl language as shell commands. perlsh
54 from the source distribution is simplistic and uninteresting, but
55 may still be what you want.
57 =head2 How do I find which modules are installed on my system?
59 You can use the ExtUtils::Installed module to show all
60 installed distributions, although it can take awhile to do
61 its magic. The standard library which comes with Perl just
62 shows up as "Perl" (although you can get those with
65 use ExtUtils::Installed;
67 my $inst = ExtUtils::Installed->new();
68 my @modules = $inst->modules();
70 If you want a list of all of the Perl module filenames, you
71 can use File::Find::Rule.
75 my @files = File::Find::Rule->file()->name( '*.pm' )->in( @INC );
77 If you do not have that module, you can do the same thing
78 with File::Find which is part of the standard library.
83 find sub { push @files, $File::Find::name if -f _ && /\.pm$/ },
86 print join "\n", @files;
88 If you simply need to quickly check to see if a module is
89 available, you can check for its documentation. If you can
90 read the documentation the module is most likely installed.
91 If you cannot read the documentation, the module might not
92 have any (in rare cases).
94 prompt% perldoc Module::Name
96 You can also try to include the module in a one-liner to see if
99 perl -MModule::Name -e1
101 =head2 How do I debug my Perl programs?
103 Have you tried C<use warnings> or used C<-w>? They enable warnings
104 to detect dubious practices.
106 Have you tried C<use strict>? It prevents you from using symbolic
107 references, makes you predeclare any subroutines that you call as bare
108 words, and (probably most importantly) forces you to predeclare your
109 variables with C<my>, C<our>, or C<use vars>.
111 Did you check the return values of each and every system call? The operating
112 system (and thus Perl) tells you whether they worked, and if not
115 open(FH, "> /etc/cantwrite")
116 or die "Couldn't write to /etc/cantwrite: $!\n";
118 Did you read L<perltrap>? It's full of gotchas for old and new Perl
119 programmers and even has sections for those of you who are upgrading
120 from languages like I<awk> and I<C>.
122 Have you tried the Perl debugger, described in L<perldebug>? You can
123 step through your program and see what it's doing and thus work out
124 why what it's doing isn't what it should be doing.
126 =head2 How do I profile my Perl programs?
128 You should get the Devel::DProf module from the standard distribution
129 (or separately on CPAN) and also use Benchmark.pm from the standard
130 distribution. The Benchmark module lets you time specific portions of
131 your code, while Devel::DProf gives detailed breakdowns of where your
132 code spends its time.
134 Here's a sample use of Benchmark:
138 @junk = `cat /etc/motd`;
142 'map' => sub { my @a = @junk;
146 'for' => sub { my @a = @junk;
152 This is what it prints (on one machine--your results will be dependent
153 on your hardware, operating system, and the load on your machine):
155 Benchmark: timing 10000 iterations of for, map...
156 for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu)
157 map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu)
159 Be aware that a good benchmark is very hard to write. It only tests the
160 data you give it and proves little about the differing complexities
161 of contrasting algorithms.
163 =head2 How do I cross-reference my Perl programs?
165 The B::Xref module can be used to generate cross-reference reports
168 perl -MO=Xref[,OPTIONS] scriptname.plx
170 =head2 Is there a pretty-printer (formatter) for Perl?
172 Perltidy is a Perl script which indents and reformats Perl scripts
173 to make them easier to read by trying to follow the rules of the
174 L<perlstyle>. If you write Perl scripts, or spend much time reading
175 them, you will probably find it useful. It is available at
176 http://perltidy.sourceforge.net
178 Of course, if you simply follow the guidelines in L<perlstyle>,
179 you shouldn't need to reformat. The habit of formatting your code
180 as you write it will help prevent bugs. Your editor can and should
181 help you with this. The perl-mode or newer cperl-mode for emacs
182 can provide remarkable amounts of help with most (but not all)
183 code, and even less programmable editors can provide significant
184 assistance. Tom Christiansen and many other VI users swear by
185 the following settings in vi and its clones:
190 Put that in your F<.exrc> file (replacing the caret characters
191 with control characters) and away you go. In insert mode, ^T is
192 for indenting, ^D is for undenting, and ^O is for blockdenting--
193 as it were. A more complete example, with comments, can be found at
194 http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz
196 The a2ps http://www-inf.enst.fr/%7Edemaille/a2ps/black+white.ps.gz does
197 lots of things related to generating nicely printed output of
198 documents, as does enscript at http://people.ssh.fi/mtr/genscript/ .
200 =head2 Is there a ctags for Perl?
202 Recent versions of ctags do much more than older versions did.
203 EXUBERANT CTAGS is available from http://ctags.sourceforge.net/
204 and does a good job of making tags files for perl code.
206 There is also a simple one at
207 http://www.cpan.org/authors/id/TOMC/scripts/ptags.gz which may do
208 the trick. It can be easy to hack this into what you want.
210 =head2 Is there an IDE or Windows Perl Editor?
212 Perl programs are just plain text, so any editor will do.
214 If you're on Unix, you already have an IDE--Unix itself. The UNIX
215 philosophy is the philosophy of several small tools that each do one
216 thing and do it well. It's like a carpenter's toolbox.
218 If you want an IDE, check the following:
224 ActiveState's cross-platform (as of April 2001 Windows and Linux),
225 multi-language IDE has Perl support, including a regular expression
226 debugger and remote debugging
227 ( http://www.ActiveState.com/Products/Komodo/index.html ). (Visual
228 Perl, a Visual Studio.NET plug-in is currently (early 2001) in beta
229 ( http://www.ActiveState.com/Products/VisualPerl/index.html )).
231 =item The Object System
233 ( http://www.castlelink.co.uk/object_system/ ) is a Perl web
234 applications development IDE, apparently for any platform
239 ( http://open-perl-ide.sourceforge.net/ )
240 Open Perl IDE is an integrated development environment for writing
241 and debugging Perl scripts with ActiveState's ActivePerl distribution
242 under Windows 95/98/NT/2000.
246 ( http://www.solutionsoft.com/perl.htm ) is an integrated development
247 environment for Windows that supports Perl development.
251 ( http://helpconsulting.net/visiperl/ )
252 From Help Consulting, for Windows.
256 ( http://www.optiperl.com/ ) is a Windows IDE with simulated CGI
257 environment, including debugger and syntax highlighting editor.
261 For editors: if you're on Unix you probably have vi or a vi clone already,
262 and possibly an emacs too, so you may not need to download anything.
263 In any emacs the cperl-mode (M-x cperl-mode) gives you perhaps the
264 best available Perl editing mode in any editor.
266 If you are using Windows, you can use any editor that lets
267 you work with plain text, such as NotePad or WordPad. Word
268 processors, such as Microsoft Word or WordPerfect, typically
269 do not work since they insert all sorts of behind-the-scenes
270 information, although some allow you to save files as "Text
271 Only". You can also download text editors designed
272 specifically for programming, such as Textpad
273 ( http://www.textpad.com/ ) and UltraEdit
274 ( http://www.ultraedit.com/ ), among others.
276 If you are using MacOS, the same concerns apply. MacPerl
277 (for Classic environments) comes with a simple editor.
278 Popular external editors are BBEdit ( http://www.bbedit.com/ )
279 or Alpha ( http://www.kelehers.org/alpha/ ). MacOS X users can
280 use Unix editors as well.
286 http://www.gnu.org/software/emacs/windows/ntemacs.html
290 http://www.microemacs.de/
294 http://www.xemacs.org/Download/index.html
298 http://space.mit.edu/~davis/jed/
302 or a vi clone such as
308 ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/
312 http://dickey.his.com/vile/vile.html
320 For vi lovers in general, Windows or elsewhere:
322 http://www.thomer.com/thomer/vi/vi.html
324 nvi ( http://www.bostic.com/vi/ , available from CPAN in src/misc/) is
325 yet another vi clone, unfortunately not available for Windows, but in
326 UNIX platforms you might be interested in trying it out, firstly because
327 strictly speaking it is not a vi clone, it is the real vi, or the new
328 incarnation of it, and secondly because you can embed Perl inside it
329 to use Perl as the scripting language. nvi is not alone in this,
330 though: at least also vim and vile offer an embedded Perl.
332 The following are Win32 multilanguage editor/IDESs that support Perl:
338 http://www.starbase.com/
342 http://www.MultiEdit.com/
346 http://www.slickedit.com/
350 There is also a toyedit Text widget based editor written in Perl
351 that is distributed with the Tk module on CPAN. The ptkdb
352 ( http://world.std.com/~aep/ptkdb/ ) is a Perl/tk based debugger that
353 acts as a development environment of sorts. Perl Composer
354 ( http://perlcomposer.sourceforge.net/ ) is an IDE for Perl/Tk
357 In addition to an editor/IDE you might be interested in a more
358 powerful shell environment for Win32. Your options include
364 from the Cygwin package ( http://sources.redhat.com/cygwin/ )
368 from the MKS Toolkit ( http://www.mks.com/ ), or the Bourne shell of
369 the U/WIN environment ( http://www.research.att.com/sw/tools/uwin/ )
373 ftp://ftp.astron.com/pub/tcsh/ , see also
374 http://www.primate.wisc.edu/software/csh-tcsh-book/
378 ftp://ftp.blarg.net/users/amol/zsh/ , see also http://www.zsh.org/
382 MKS and U/WIN are commercial (U/WIN is free for educational and
383 research purposes), Cygwin is covered by the GNU Public License (but
384 that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all
385 contain (in addition to the shells) a comprehensive set of standard
386 UNIX toolkit utilities.
388 If you're transferring text files between Unix and Windows using FTP
389 be sure to transfer them in ASCII mode so the ends of lines are
390 appropriately converted.
392 On Mac OS the MacPerl Application comes with a simple 32k text editor
393 that behaves like a rudimentary IDE. In contrast to the MacPerl Application
394 the MPW Perl tool can make use of the MPW Shell itself as an editor (with
399 =item BBEdit and BBEdit Lite
401 are text editors for Mac OS that have a Perl sensitivity mode
402 ( http://web.barebones.com/ ).
406 is an editor, written and extensible in Tcl, that nonetheless has
407 built in support for several popular markup and programming languages
408 including Perl and HTML ( http://alpha.olm.net/ ).
412 Pepper and Pe are programming language sensitive text editors for Mac
413 OS X and BeOS respectively ( http://www.hekkelman.com/ ).
415 =head2 Where can I get Perl macros for vi?
417 For a complete version of Tom Christiansen's vi configuration file,
418 see http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz ,
419 the standard benchmark file for vi emulators. The file runs best with nvi,
420 the current version of vi out of Berkeley, which incidentally can be built
421 with an embedded Perl interpreter--see http://www.cpan.org/src/misc/ .
423 =head2 Where can I get perl-mode for emacs?
425 Since Emacs version 19 patchlevel 22 or so, there have been both a
426 perl-mode.el and support for the Perl debugger built in. These should
427 come with the standard Emacs 19 distribution.
429 In the Perl source directory, you'll find a directory called "emacs",
430 which contains a cperl-mode that color-codes keywords, provides
431 context-sensitive help, and other nifty things.
433 Note that the perl-mode of emacs will have fits with C<"main'foo">
434 (single quote), and mess up the indentation and highlighting. You
435 are probably using C<"main::foo"> in new Perl code anyway, so this
436 shouldn't be an issue.
438 =head2 How can I use curses with Perl?
440 The Curses module from CPAN provides a dynamically loadable object
441 module interface to a curses library. A small demo can be found at the
442 directory http://www.cpan.org/authors/Tom_Christiansen/scripts/rep.gz ;
443 this program repeats a command and updates the screen as needed, rendering
444 B<rep ps axu> similar to B<top>.
446 =head2 How can I use X or Tk with Perl?
448 Tk is a completely Perl-based, object-oriented interface to the Tk toolkit
449 that doesn't force you to use Tcl just to get at Tk. Sx is an interface
450 to the Athena Widget set. Both are available from CPAN. See the
451 directory http://www.cpan.org/modules/by-category/08_User_Interfaces/
453 Invaluable for Perl/Tk programming are the Perl/Tk FAQ at
454 http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference
456 http://www.cpan.org/authors/Stephen_O_Lidie/ , and the
458 http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html .
460 =head2 How can I generate simple menus without using CGI or Tk?
462 The http://www.cpan.org/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
463 module, which is curses-based, can help with this.
465 =head2 How can I make my Perl program run faster?
467 The best way to do this is to come up with a better algorithm. This
468 can often make a dramatic difference. Jon Bentley's book
469 I<Programming Pearls> (that's not a misspelling!) has some good tips
470 on optimization, too. Advice on benchmarking boils down to: benchmark
471 and profile to make sure you're optimizing the right part, look for
472 better algorithms instead of microtuning your code, and when all else
473 fails consider just buying faster hardware. You will probably want to
474 read the answer to the earlier question ``How do I profile my Perl
475 programs?'' if you haven't done so already.
477 A different approach is to autoload seldom-used Perl code. See the
478 AutoSplit and AutoLoader modules in the standard distribution for
479 that. Or you could locate the bottleneck and think about writing just
480 that part in C, the way we used to take bottlenecks in C code and
481 write them in assembler. Similar to rewriting in C, modules that have
482 critical sections can be written in C (for instance, the PDL module
485 If you're currently linking your perl executable to a shared
486 I<libc.so>, you can often gain a 10-25% performance benefit by
487 rebuilding it to link with a static libc.a instead. This will make a
488 bigger perl executable, but your Perl programs (and programmers) may
489 thank you for it. See the F<INSTALL> file in the source distribution
490 for more information.
492 The undump program was an ancient attempt to speed up Perl program by
493 storing the already-compiled form to disk. This is no longer a viable
494 option, as it only worked on a few architectures, and wasn't a good
497 =head2 How can I make my Perl program take less memory?
499 When it comes to time-space tradeoffs, Perl nearly always prefers to
500 throw memory at a problem. Scalars in Perl use more memory than
501 strings in C, arrays take more than that, and hashes use even more. While
502 there's still a lot to be done, recent releases have been addressing
503 these issues. For example, as of 5.004, duplicate hash keys are
504 shared amongst all hashes using them, so require no reallocation.
506 In some cases, using substr() or vec() to simulate arrays can be
507 highly beneficial. For example, an array of a thousand booleans will
508 take at least 20,000 bytes of space, but it can be turned into one
509 125-byte bit vector--a considerable memory savings. The standard
510 Tie::SubstrHash module can also help for certain types of data
511 structure. If you're working with specialist data structures
512 (matrices, for instance) modules that implement these in C may use
513 less memory than equivalent Perl modules.
515 Another thing to try is learning whether your Perl was compiled with
516 the system malloc or with Perl's builtin malloc. Whichever one it
517 is, try using the other one and see whether this makes a difference.
518 Information about malloc is in the F<INSTALL> file in the source
519 distribution. You can find out whether you are using perl's malloc by
520 typing C<perl -V:usemymalloc>.
522 Of course, the best way to save memory is to not do anything to waste
523 it in the first place. Good programming practices can go a long way
530 Don't read an entire file into memory if you can process it line
531 by line. Or more concretely, use a loop like this:
550 When the files you're processing are small, it doesn't much matter which
551 way you do it, but it makes a huge difference when they start getting
554 =item * Use map and grep selectively
556 Remember that both map and grep expect a LIST argument, so doing this:
558 @wanted = grep {/pattern/} <FILE>;
560 will cause the entire file to be slurped. For large files, it's better
564 push(@wanted, $_) if /pattern/;
567 =item * Avoid unnecessary quotes and stringification
569 Don't quote large strings unless absolutely necessary:
571 my $copy = "$large_string";
573 makes 2 copies of $large_string (one for $copy and another for the
576 my $copy = $large_string;
580 Ditto for stringifying large arrays:
587 is much more memory-efficient than either
589 print join "\n", @big_array;
599 =item * Pass by reference
601 Pass arrays and hashes by reference, not by value. For one thing, it's
602 the only way to pass multiple lists or hashes (or both) in a single
603 call/return. It also avoids creating a copy of all the contents. This
604 requires some judgment, however, because any changes will be propagated
605 back to the original data. If you really want to mangle (er, modify) a
606 copy, you'll have to sacrifice the memory needed to make one.
608 =item * Tie large variables to disk.
610 For "big" data stores (i.e. ones that exceed available memory) consider
611 using one of the DB modules to store it on disk instead of in RAM. This
612 will incur a penalty in access time, but that's probably better than
613 causing your hard disk to thrash due to massive swapping.
617 =head2 Is it safe to return a reference to local or lexical data?
619 Yes. Perl's garbage collection system takes care of this so
620 everything works out right.
628 push @many, makeone();
631 print $many[4][5], "\n";
635 =head2 How can I free an array or hash so my program shrinks?
637 You usually can't. On most operating systems, memory
638 allocated to a program can never be returned to the system.
639 That's why long-running programs sometimes re-exec
640 themselves. Some operating systems (notably, systems that
641 use mmap(2) for allocating large chunks of memory) can
642 reclaim memory that is no longer used, but on such systems,
643 perl must be configured and compiled to use the OS's malloc,
646 However, judicious use of my() on your variables will help make sure
647 that they go out of scope so that Perl can free up that space for
648 use in other parts of your program. A global variable, of course, never
649 goes out of scope, so you can't get its space automatically reclaimed,
650 although undef()ing and/or delete()ing it will achieve the same effect.
651 In general, memory allocation and de-allocation isn't something you can
652 or should be worrying about much in Perl, but even this capability
653 (preallocation of data types) is in the works.
655 =head2 How can I make my CGI script more efficient?
657 Beyond the normal measures described to make general Perl programs
658 faster or smaller, a CGI program has additional issues. It may be run
659 several times per second. Given that each time it runs it will need
660 to be re-compiled and will often allocate a megabyte or more of system
661 memory, this can be a killer. Compiling into C B<isn't going to help
662 you> because the process start-up overhead is where the bottleneck is.
664 There are two popular ways to avoid this overhead. One solution
665 involves running the Apache HTTP server (available from
666 http://www.apache.org/ ) with either of the mod_perl or mod_fastcgi
669 With mod_perl and the Apache::Registry module (distributed with
670 mod_perl), httpd will run with an embedded Perl interpreter which
671 pre-compiles your script and then executes it within the same address
672 space without forking. The Apache extension also gives Perl access to
673 the internal server API, so modules written in Perl can do just about
674 anything a module written in C can. For more on mod_perl, see
675 http://perl.apache.org/
677 With the FCGI module (from CPAN) and the mod_fastcgi
678 module (available from http://www.fastcgi.com/ ) each of your Perl
679 programs becomes a permanent CGI daemon process.
681 Both of these solutions can have far-reaching effects on your system
682 and on the way you write your CGI programs, so investigate them with
685 See http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
687 A non-free, commercial product, ``The Velocity Engine for Perl'',
688 (http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ )
689 might also be worth looking at. It will allow you to increase the
690 performance of your Perl programs, running programs up to 25 times
691 faster than normal CGI Perl when running in persistent Perl mode or 4
692 to 5 times faster without any modification to your existing CGI
693 programs. Fully functional evaluation copies are available from the
696 =head2 How can I hide the source for my Perl program?
698 Delete it. :-) Seriously, there are a number of (mostly
699 unsatisfactory) solutions with varying levels of ``security''.
701 First of all, however, you I<can't> take away read permission, because
702 the source code has to be readable in order to be compiled and
703 interpreted. (That doesn't mean that a CGI script's source is
704 readable by people on the web, though--only by people with access to
705 the filesystem.) So you have to leave the permissions at the socially
708 Some people regard this as a security problem. If your program does
709 insecure things and relies on people not knowing how to exploit those
710 insecurities, it is not secure. It is often possible for someone to
711 determine the insecure things and exploit them without viewing the
712 source. Security through obscurity, the name for hiding your bugs
713 instead of fixing them, is little security indeed.
715 You can try using encryption via source filters (Starting from Perl
716 5.8 the Filter::Simple and Filter::Util::Call modules are included in
717 the standard distribution), but any decent programmer will be able to
718 decrypt it. You can try using the byte code compiler and interpreter
719 described below, but the curious might still be able to de-compile it.
720 You can try using the native-code compiler described below, but
721 crackers might be able to disassemble it. These pose varying degrees
722 of difficulty to people wanting to get at your code, but none can
723 definitively conceal it (true of every language, not just Perl).
725 It is very easy to recover the source of Perl programs. You simply
726 feed the program to the perl interpreter and use the modules in
727 the B:: hierarchy. The B::Deparse module should be able to
728 defeat most attempts to hide source. Again, this is not
731 If you're concerned about people profiting from your code, then the
732 bottom line is that nothing but a restrictive license will give you
733 legal security. License your software and pepper it with threatening
734 statements like ``This is unpublished proprietary software of XYZ Corp.
735 Your access to it does not give you permission to use it blah blah
736 blah.'' We are not lawyers, of course, so you should see a lawyer if
737 you want to be sure your license's wording will stand up in court.
739 =head2 How can I compile my Perl program into byte code or C?
741 Malcolm Beattie has written a multifunction backend compiler,
742 available from CPAN, that can do both these things. It is included
743 in the perl5.005 release, but is still considered experimental.
744 This means it's fun to play with if you're a programmer but not
745 really for people looking for turn-key solutions.
747 Merely compiling into C does not in and of itself guarantee that your
748 code will run very much faster. That's because except for lucky cases
749 where a lot of native type inferencing is possible, the normal Perl
750 run-time system is still present and so your program will take just as
751 long to run and be just as big. Most programs save little more than
752 compilation time, leaving execution no more than 10-30% faster. A few
753 rare programs actually benefit significantly (even running several times
754 faster), but this takes some tweaking of your code.
756 You'll probably be astonished to learn that the current version of the
757 compiler generates a compiled form of your script whose executable is
758 just as big as the original perl executable, and then some. That's
759 because as currently written, all programs are prepared for a full
760 eval() statement. You can tremendously reduce this cost by building a
761 shared I<libperl.so> library and linking against that. See the
762 F<INSTALL> podfile in the Perl source distribution for details. If
763 you link your main perl binary with this, it will make it minuscule.
764 For example, on one author's system, F</usr/bin/perl> is only 11k in
767 In general, the compiler will do nothing to make a Perl program smaller,
768 faster, more portable, or more secure. In fact, it can make your
769 situation worse. The executable will be bigger, your VM system may take
770 longer to load the whole thing, the binary is fragile and hard to fix,
771 and compilation never stopped software piracy in the form of crackers,
772 viruses, or bootleggers. The real advantage of the compiler is merely
773 packaging, and once you see the size of what it makes (well, unless
774 you use a shared I<libperl.so>), you'll probably want a complete
777 =head2 How can I compile Perl into Java?
779 You can also integrate Java and Perl with the
780 Perl Resource Kit from O'Reilly and Associates. See
781 http://www.oreilly.com/catalog/prkunix/ .
783 Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in
784 development, allows Perl code to be called from Java. See jpl/README
785 in the Perl source tree.
787 =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
791 extproc perl -S -your_switches
793 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
794 `extproc' handling). For DOS one should first invent a corresponding
795 batch file and codify it in C<ALTERNATIVE_SHEBANG> (see the
796 F<INSTALL> file in the source distribution for more information).
798 The Win95/NT installation, when using the ActiveState port of Perl,
799 will modify the Registry to associate the C<.pl> extension with the
800 perl interpreter. If you install another port, perhaps even building
801 your own Win95/NT Perl from the standard sources by using a Windows port
802 of gcc (e.g., with cygwin or mingw32), then you'll have to modify
803 the Registry yourself. In addition to associating C<.pl> with the
804 interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them
805 run the program C<install-linux.pl> merely by typing C<install-linux>.
807 Macintosh Perl programs will have the appropriate Creator and
808 Type, so that double-clicking them will invoke the Perl application.
810 I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
811 throw the perl interpreter into your cgi-bin directory, in order to
812 get your programs working for a web server. This is an EXTREMELY big
813 security risk. Take the time to figure out how to do it correctly.
815 =head2 Can I write useful Perl programs on the command line?
817 Yes. Read L<perlrun> for more information. Some examples follow.
818 (These assume standard Unix shell quoting rules.)
820 # sum first and last fields
821 perl -lane 'print $F[0] + $F[-1]' *
823 # identify text files
824 perl -le 'for(@ARGV) {print if -f && -T _}' *
826 # remove (most) comments from C program
827 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
829 # make file a month younger than today, defeating reaper daemons
830 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
832 # find first unused uid
833 perl -le '$i++ while getpwuid($i); print $i'
835 # display reasonable manpath
836 echo $PATH | perl -nl -072 -e '
837 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
839 OK, the last one was actually an Obfuscated Perl Contest entry. :-)
841 =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system?
843 The problem is usually that the command interpreters on those systems
844 have rather different ideas about quoting than the Unix shells under
845 which the one-liners were created. On some systems, you may have to
846 change single-quotes to double ones, which you must I<NOT> do on Unix
847 or Plan9 systems. You might also have to change a single % to a %%.
852 perl -e 'print "Hello world\n"'
855 perl -e "print \"Hello world\n\""
858 print "Hello world\n"
859 (then Run "Myscript" or Shift-Command-R)
862 perl -e 'print "Hello world\n"'
865 perl -e "print ""Hello world\n"""
867 The problem is that none of these examples are reliable: they depend on the
868 command interpreter. Under Unix, the first two often work. Under DOS,
869 it's entirely possible that neither works. If 4DOS was the command shell,
870 you'd probably have better luck like this:
872 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
874 Under the Mac, it depends which environment you are using. The MacPerl
875 shell, or MPW, is much like Unix shells in its support for several
876 quoting variants, except that it makes free use of the Mac's non-ASCII
877 characters as control characters.
879 Using qq(), q(), and qx(), instead of "double quotes", 'single
880 quotes', and `backticks`, may make one-liners easier to write.
882 There is no general solution to all of this. It is a mess.
884 [Some of this answer was contributed by Kenneth Albanowski.]
886 =head2 Where can I learn about CGI or Web programming in Perl?
888 For modules, get the CGI or LWP modules from CPAN. For textbooks,
889 see the two especially dedicated to web stuff in the question on
890 books. For problems and questions related to the web, like ``Why
891 do I get 500 Errors'' or ``Why doesn't it run from the browser right
892 when it runs fine on the command line'', see the troubleshooting
893 guides and references in L<perlfaq9> or in the CGI MetaFAQ:
895 http://www.perl.org/CGI_MetaFAQ.html
897 =head2 Where can I learn about object-oriented Perl programming?
899 A good place to start is L<perltoot>, and you can use L<perlobj>,
900 L<perlboot>, L<perltoot>, L<perltooc>, and L<perlbot> for reference.
901 (If you are using really old Perl, you may not have all of these,
902 try http://www.perldoc.com/ , but consider upgrading your perl.)
904 A good book on OO on Perl is the "Object-Oriented Perl"
905 by Damian Conway from Manning Publications,
906 http://www.manning.com/Conway/index.html
908 =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp]
910 If you want to call C from Perl, start with L<perlxstut>,
911 moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to
912 call Perl from C, then read L<perlembed>, L<perlcall>, and
913 L<perlguts>. Don't forget that you can learn a lot from looking at
914 how the authors of existing extension modules wrote their code and
915 solved their problems.
917 =head2 I've read perlembed, perlguts, etc., but I can't embed perl in
918 my C program; what am I doing wrong?
920 Download the ExtUtils::Embed kit from CPAN and run `make test'. If
921 the tests pass, read the pods again and again and again. If they
922 fail, see L<perlbug> and send a bug report with the output of
923 C<make test TEST_VERBOSE=1> along with C<perl -V>.
925 =head2 When I tried to run my script, I got this message. What does it mean?
927 A complete list of Perl's error messages and warnings with explanatory
928 text can be found in L<perldiag>. You can also use the splain program
929 (distributed with Perl) to explain the error messages:
931 perl program 2>diag.out
932 splain [-v] [-p] diag.out
934 or change your program to explain the messages for you:
940 use diagnostics -verbose;
942 =head2 What's MakeMaker?
944 This module (part of the standard Perl distribution) is designed to
945 write a Makefile for an extension module from a Makefile.PL. For more
946 information, see L<ExtUtils::MakeMaker>.
948 =head1 AUTHOR AND COPYRIGHT
950 Copyright (c) 1997-2002 Tom Christiansen and Nathan Torkington.
953 This documentation is free; you can redistribute it and/or modify it
954 under the same terms as Perl itself.
956 Irrespective of its distribution, all code examples here are in the public
957 domain. You are permitted and encouraged to use this code and any
958 derivatives thereof in your own programs for fun or for profit as you
959 see fit. A simple comment in the code giving credit to the FAQ would
960 be courteous but is not required.