3 perlfaq3 - Programming Tools ($Revision: 1.35 $, $Date: 2003/08/24 05:26:59 $)
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;
151 'for' => sub { my @a = @junk;
157 This is what it prints (on one machine--your results will be dependent
158 on your hardware, operating system, and the load on your machine):
160 Benchmark: timing 10000 iterations of for, map...
161 for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu)
162 map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu)
164 Be aware that a good benchmark is very hard to write. It only tests the
165 data you give it and proves little about the differing complexities
166 of contrasting algorithms.
168 =head2 How do I cross-reference my Perl programs?
170 The B::Xref module can be used to generate cross-reference reports
173 perl -MO=Xref[,OPTIONS] scriptname.plx
175 =head2 Is there a pretty-printer (formatter) for Perl?
177 Perltidy is a Perl script which indents and reformats Perl scripts
178 to make them easier to read by trying to follow the rules of the
179 L<perlstyle>. If you write Perl scripts, or spend much time reading
180 them, you will probably find it useful. It is available at
181 http://perltidy.sourceforge.net
183 Of course, if you simply follow the guidelines in L<perlstyle>,
184 you shouldn't need to reformat. The habit of formatting your code
185 as you write it will help prevent bugs. Your editor can and should
186 help you with this. The perl-mode or newer cperl-mode for emacs
187 can provide remarkable amounts of help with most (but not all)
188 code, and even less programmable editors can provide significant
189 assistance. Tom Christiansen and many other VI users swear by
190 the following settings in vi and its clones:
195 Put that in your F<.exrc> file (replacing the caret characters
196 with control characters) and away you go. In insert mode, ^T is
197 for indenting, ^D is for undenting, and ^O is for blockdenting--
198 as it were. A more complete example, with comments, can be found at
199 http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz
201 The a2ps http://www-inf.enst.fr/%7Edemaille/a2ps/black+white.ps.gz does
202 lots of things related to generating nicely printed output of
203 documents, as does enscript at http://people.ssh.fi/mtr/genscript/ .
205 =head2 Is there a ctags for Perl?
207 Recent versions of ctags do much more than older versions did.
208 EXUBERANT CTAGS is available from http://ctags.sourceforge.net/
209 and does a good job of making tags files for perl code.
211 There is also a simple one at
212 http://www.cpan.org/authors/id/TOMC/scripts/ptags.gz which may do
213 the trick. It can be easy to hack this into what you want.
215 =head2 Is there an IDE or Windows Perl Editor?
217 Perl programs are just plain text, so any editor will do.
219 If you're on Unix, you already have an IDE--Unix itself. The UNIX
220 philosophy is the philosophy of several small tools that each do one
221 thing and do it well. It's like a carpenter's toolbox.
223 If you want an IDE, check the following:
229 ActiveState's cross-platform (as of April 2001 Windows and Linux),
230 multi-language IDE has Perl support, including a regular expression
231 debugger and remote debugging
232 ( http://www.ActiveState.com/Products/Komodo/index.html ). (Visual
233 Perl, a Visual Studio.NET plug-in is currently (early 2001) in beta
234 ( http://www.ActiveState.com/Products/VisualPerl/index.html )).
236 =item The Object System
238 ( http://www.castlelink.co.uk/object_system/ ) is a Perl web
239 applications development IDE, apparently for any platform
244 ( http://open-perl-ide.sourceforge.net/ )
245 Open Perl IDE is an integrated development environment for writing
246 and debugging Perl scripts with ActiveState's ActivePerl distribution
247 under Windows 95/98/NT/2000.
251 ( http://www.solutionsoft.com/perl.htm ) is an integrated development
252 environment for Windows that supports Perl development.
256 ( http://helpconsulting.net/visiperl/ )
257 From Help Consulting, for Windows.
261 ( http://www.optiperl.com/ ) is a Windows IDE with simulated CGI
262 environment, including debugger and syntax highlighting editor.
266 For editors: if you're on Unix you probably have vi or a vi clone already,
267 and possibly an emacs too, so you may not need to download anything.
268 In any emacs the cperl-mode (M-x cperl-mode) gives you perhaps the
269 best available Perl editing mode in any editor.
271 If you are using Windows, you can use any editor that lets
272 you work with plain text, such as NotePad or WordPad. Word
273 processors, such as Microsoft Word or WordPerfect, typically
274 do not work since they insert all sorts of behind-the-scenes
275 information, although some allow you to save files as "Text
276 Only". You can also download text editors designed
277 specifically for programming, such as Textpad
278 ( http://www.textpad.com/ ) and UltraEdit
279 ( http://www.ultraedit.com/ ), among others.
281 If you are using MacOS, the same concerns apply. MacPerl
282 (for Classic environments) comes with a simple editor.
283 Popular external editors are BBEdit ( http://www.bbedit.com/ )
284 or Alpha ( http://www.kelehers.org/alpha/ ). MacOS X users can
285 use Unix editors as well.
291 http://www.gnu.org/software/emacs/windows/ntemacs.html
295 http://www.microemacs.de/
299 http://www.xemacs.org/Download/index.html
303 http://space.mit.edu/~davis/jed/
307 or a vi clone such as
313 ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/
317 http://dickey.his.com/vile/vile.html
325 For vi lovers in general, Windows or elsewhere:
327 http://www.thomer.com/thomer/vi/vi.html
329 nvi ( http://www.bostic.com/vi/ , available from CPAN in src/misc/) is
330 yet another vi clone, unfortunately not available for Windows, but in
331 UNIX platforms you might be interested in trying it out, firstly because
332 strictly speaking it is not a vi clone, it is the real vi, or the new
333 incarnation of it, and secondly because you can embed Perl inside it
334 to use Perl as the scripting language. nvi is not alone in this,
335 though: at least also vim and vile offer an embedded Perl.
337 The following are Win32 multilanguage editor/IDESs that support Perl:
343 http://www.starbase.com/
347 http://www.MultiEdit.com/
351 http://www.slickedit.com/
355 There is also a toyedit Text widget based editor written in Perl
356 that is distributed with the Tk module on CPAN. The ptkdb
357 ( http://world.std.com/~aep/ptkdb/ ) is a Perl/tk based debugger that
358 acts as a development environment of sorts. Perl Composer
359 ( http://perlcomposer.sourceforge.net/ ) is an IDE for Perl/Tk
362 In addition to an editor/IDE you might be interested in a more
363 powerful shell environment for Win32. Your options include
369 from the Cygwin package ( http://sources.redhat.com/cygwin/ )
373 from the MKS Toolkit ( http://www.mks.com/ ), or the Bourne shell of
374 the U/WIN environment ( http://www.research.att.com/sw/tools/uwin/ )
378 ftp://ftp.astron.com/pub/tcsh/ , see also
379 http://www.primate.wisc.edu/software/csh-tcsh-book/
383 ftp://ftp.blarg.net/users/amol/zsh/ , see also http://www.zsh.org/
387 MKS and U/WIN are commercial (U/WIN is free for educational and
388 research purposes), Cygwin is covered by the GNU Public License (but
389 that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all
390 contain (in addition to the shells) a comprehensive set of standard
391 UNIX toolkit utilities.
393 If you're transferring text files between Unix and Windows using FTP
394 be sure to transfer them in ASCII mode so the ends of lines are
395 appropriately converted.
397 On Mac OS the MacPerl Application comes with a simple 32k text editor
398 that behaves like a rudimentary IDE. In contrast to the MacPerl Application
399 the MPW Perl tool can make use of the MPW Shell itself as an editor (with
404 =item BBEdit and BBEdit Lite
406 are text editors for Mac OS that have a Perl sensitivity mode
407 ( http://web.barebones.com/ ).
411 is an editor, written and extensible in Tcl, that nonetheless has
412 built in support for several popular markup and programming languages
413 including Perl and HTML ( http://alpha.olm.net/ ).
417 Pepper and Pe are programming language sensitive text editors for Mac
418 OS X and BeOS respectively ( http://www.hekkelman.com/ ).
420 =head2 Where can I get Perl macros for vi?
422 For a complete version of Tom Christiansen's vi configuration file,
423 see http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz ,
424 the standard benchmark file for vi emulators. The file runs best with nvi,
425 the current version of vi out of Berkeley, which incidentally can be built
426 with an embedded Perl interpreter--see http://www.cpan.org/src/misc/ .
428 =head2 Where can I get perl-mode for emacs?
430 Since Emacs version 19 patchlevel 22 or so, there have been both a
431 perl-mode.el and support for the Perl debugger built in. These should
432 come with the standard Emacs 19 distribution.
434 In the Perl source directory, you'll find a directory called "emacs",
435 which contains a cperl-mode that color-codes keywords, provides
436 context-sensitive help, and other nifty things.
438 Note that the perl-mode of emacs will have fits with C<"main'foo">
439 (single quote), and mess up the indentation and highlighting. You
440 are probably using C<"main::foo"> in new Perl code anyway, so this
441 shouldn't be an issue.
443 =head2 How can I use curses with Perl?
445 The Curses module from CPAN provides a dynamically loadable object
446 module interface to a curses library. A small demo can be found at the
447 directory http://www.cpan.org/authors/Tom_Christiansen/scripts/rep.gz ;
448 this program repeats a command and updates the screen as needed, rendering
449 B<rep ps axu> similar to B<top>.
451 =head2 How can I use X or Tk with Perl?
453 Tk is a completely Perl-based, object-oriented interface to the Tk toolkit
454 that doesn't force you to use Tcl just to get at Tk. Sx is an interface
455 to the Athena Widget set. Both are available from CPAN. See the
456 directory http://www.cpan.org/modules/by-category/08_User_Interfaces/
458 Invaluable for Perl/Tk programming are the Perl/Tk FAQ at
459 http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference
461 http://www.cpan.org/authors/Stephen_O_Lidie/ , and the
463 http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html .
465 =head2 How can I generate simple menus without using CGI or Tk?
467 The http://www.cpan.org/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
468 module, which is curses-based, can help with this.
470 =head2 How can I make my Perl program run faster?
472 The best way to do this is to come up with a better algorithm. This
473 can often make a dramatic difference. Jon Bentley's book
474 I<Programming Pearls> (that's not a misspelling!) has some good tips
475 on optimization, too. Advice on benchmarking boils down to: benchmark
476 and profile to make sure you're optimizing the right part, look for
477 better algorithms instead of microtuning your code, and when all else
478 fails consider just buying faster hardware. You will probably want to
479 read the answer to the earlier question ``How do I profile my Perl
480 programs?'' if you haven't done so already.
482 A different approach is to autoload seldom-used Perl code. See the
483 AutoSplit and AutoLoader modules in the standard distribution for
484 that. Or you could locate the bottleneck and think about writing just
485 that part in C, the way we used to take bottlenecks in C code and
486 write them in assembler. Similar to rewriting in C, modules that have
487 critical sections can be written in C (for instance, the PDL module
490 If you're currently linking your perl executable to a shared
491 I<libc.so>, you can often gain a 10-25% performance benefit by
492 rebuilding it to link with a static libc.a instead. This will make a
493 bigger perl executable, but your Perl programs (and programmers) may
494 thank you for it. See the F<INSTALL> file in the source distribution
495 for more information.
497 The undump program was an ancient attempt to speed up Perl program by
498 storing the already-compiled form to disk. This is no longer a viable
499 option, as it only worked on a few architectures, and wasn't a good
502 =head2 How can I make my Perl program take less memory?
504 When it comes to time-space tradeoffs, Perl nearly always prefers to
505 throw memory at a problem. Scalars in Perl use more memory than
506 strings in C, arrays take more than that, and hashes use even more. While
507 there's still a lot to be done, recent releases have been addressing
508 these issues. For example, as of 5.004, duplicate hash keys are
509 shared amongst all hashes using them, so require no reallocation.
511 In some cases, using substr() or vec() to simulate arrays can be
512 highly beneficial. For example, an array of a thousand booleans will
513 take at least 20,000 bytes of space, but it can be turned into one
514 125-byte bit vector--a considerable memory savings. The standard
515 Tie::SubstrHash module can also help for certain types of data
516 structure. If you're working with specialist data structures
517 (matrices, for instance) modules that implement these in C may use
518 less memory than equivalent Perl modules.
520 Another thing to try is learning whether your Perl was compiled with
521 the system malloc or with Perl's builtin malloc. Whichever one it
522 is, try using the other one and see whether this makes a difference.
523 Information about malloc is in the F<INSTALL> file in the source
524 distribution. You can find out whether you are using perl's malloc by
525 typing C<perl -V:usemymalloc>.
527 Of course, the best way to save memory is to not do anything to waste
528 it in the first place. Good programming practices can go a long way
535 Don't read an entire file into memory if you can process it line
536 by line. Or more concretely, use a loop like this:
555 When the files you're processing are small, it doesn't much matter which
556 way you do it, but it makes a huge difference when they start getting
559 =item * Use map and grep selectively
561 Remember that both map and grep expect a LIST argument, so doing this:
563 @wanted = grep {/pattern/} <FILE>;
565 will cause the entire file to be slurped. For large files, it's better
569 push(@wanted, $_) if /pattern/;
572 =item * Avoid unnecessary quotes and stringification
574 Don't quote large strings unless absolutely necessary:
576 my $copy = "$large_string";
578 makes 2 copies of $large_string (one for $copy and another for the
581 my $copy = $large_string;
585 Ditto for stringifying large arrays:
592 is much more memory-efficient than either
594 print join "\n", @big_array;
604 =item * Pass by reference
606 Pass arrays and hashes by reference, not by value. For one thing, it's
607 the only way to pass multiple lists or hashes (or both) in a single
608 call/return. It also avoids creating a copy of all the contents. This
609 requires some judgment, however, because any changes will be propagated
610 back to the original data. If you really want to mangle (er, modify) a
611 copy, you'll have to sacrifice the memory needed to make one.
613 =item * Tie large variables to disk.
615 For "big" data stores (i.e. ones that exceed available memory) consider
616 using one of the DB modules to store it on disk instead of in RAM. This
617 will incur a penalty in access time, but that's probably better than
618 causing your hard disk to thrash due to massive swapping.
622 =head2 Is it safe to return a reference to local or lexical data?
624 Yes. Perl's garbage collection system takes care of this so
625 everything works out right.
633 push @many, makeone();
636 print $many[4][5], "\n";
640 =head2 How can I free an array or hash so my program shrinks?
642 You usually can't. On most operating systems, memory
643 allocated to a program can never be returned to the system.
644 That's why long-running programs sometimes re-exec
645 themselves. Some operating systems (notably, systems that
646 use mmap(2) for allocating large chunks of memory) can
647 reclaim memory that is no longer used, but on such systems,
648 perl must be configured and compiled to use the OS's malloc,
651 However, judicious use of my() on your variables will help make sure
652 that they go out of scope so that Perl can free up that space for
653 use in other parts of your program. A global variable, of course, never
654 goes out of scope, so you can't get its space automatically reclaimed,
655 although undef()ing and/or delete()ing it will achieve the same effect.
656 In general, memory allocation and de-allocation isn't something you can
657 or should be worrying about much in Perl, but even this capability
658 (preallocation of data types) is in the works.
660 =head2 How can I make my CGI script more efficient?
662 Beyond the normal measures described to make general Perl programs
663 faster or smaller, a CGI program has additional issues. It may be run
664 several times per second. Given that each time it runs it will need
665 to be re-compiled and will often allocate a megabyte or more of system
666 memory, this can be a killer. Compiling into C B<isn't going to help
667 you> because the process start-up overhead is where the bottleneck is.
669 There are two popular ways to avoid this overhead. One solution
670 involves running the Apache HTTP server (available from
671 http://www.apache.org/ ) with either of the mod_perl or mod_fastcgi
674 With mod_perl and the Apache::Registry module (distributed with
675 mod_perl), httpd will run with an embedded Perl interpreter which
676 pre-compiles your script and then executes it within the same address
677 space without forking. The Apache extension also gives Perl access to
678 the internal server API, so modules written in Perl can do just about
679 anything a module written in C can. For more on mod_perl, see
680 http://perl.apache.org/
682 With the FCGI module (from CPAN) and the mod_fastcgi
683 module (available from http://www.fastcgi.com/ ) each of your Perl
684 programs becomes a permanent CGI daemon process.
686 Both of these solutions can have far-reaching effects on your system
687 and on the way you write your CGI programs, so investigate them with
690 See http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
692 A non-free, commercial product, ``The Velocity Engine for Perl'',
693 (http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ )
694 might also be worth looking at. It will allow you to increase the
695 performance of your Perl programs, running programs up to 25 times
696 faster than normal CGI Perl when running in persistent Perl mode or 4
697 to 5 times faster without any modification to your existing CGI
698 programs. Fully functional evaluation copies are available from the
701 =head2 How can I hide the source for my Perl program?
703 Delete it. :-) Seriously, there are a number of (mostly
704 unsatisfactory) solutions with varying levels of ``security''.
706 First of all, however, you I<can't> take away read permission, because
707 the source code has to be readable in order to be compiled and
708 interpreted. (That doesn't mean that a CGI script's source is
709 readable by people on the web, though--only by people with access to
710 the filesystem.) So you have to leave the permissions at the socially
713 Some people regard this as a security problem. If your program does
714 insecure things and relies on people not knowing how to exploit those
715 insecurities, it is not secure. It is often possible for someone to
716 determine the insecure things and exploit them without viewing the
717 source. Security through obscurity, the name for hiding your bugs
718 instead of fixing them, is little security indeed.
720 You can try using encryption via source filters (Starting from Perl
721 5.8 the Filter::Simple and Filter::Util::Call modules are included in
722 the standard distribution), but any decent programmer will be able to
723 decrypt it. You can try using the byte code compiler and interpreter
724 described below, but the curious might still be able to de-compile it.
725 You can try using the native-code compiler described below, but
726 crackers might be able to disassemble it. These pose varying degrees
727 of difficulty to people wanting to get at your code, but none can
728 definitively conceal it (true of every language, not just Perl).
730 It is very easy to recover the source of Perl programs. You simply
731 feed the program to the perl interpreter and use the modules in
732 the B:: hierarchy. The B::Deparse module should be able to
733 defeat most attempts to hide source. Again, this is not
736 If you're concerned about people profiting from your code, then the
737 bottom line is that nothing but a restrictive license will give you
738 legal security. License your software and pepper it with threatening
739 statements like ``This is unpublished proprietary software of XYZ Corp.
740 Your access to it does not give you permission to use it blah blah
741 blah.'' We are not lawyers, of course, so you should see a lawyer if
742 you want to be sure your license's wording will stand up in court.
744 =head2 How can I compile my Perl program into byte code or C?
746 Malcolm Beattie has written a multifunction backend compiler,
747 available from CPAN, that can do both these things. It is included
748 in the perl5.005 release, but is still considered experimental.
749 This means it's fun to play with if you're a programmer but not
750 really for people looking for turn-key solutions.
752 Merely compiling into C does not in and of itself guarantee that your
753 code will run very much faster. That's because except for lucky cases
754 where a lot of native type inferencing is possible, the normal Perl
755 run-time system is still present and so your program will take just as
756 long to run and be just as big. Most programs save little more than
757 compilation time, leaving execution no more than 10-30% faster. A few
758 rare programs actually benefit significantly (even running several times
759 faster), but this takes some tweaking of your code.
761 You'll probably be astonished to learn that the current version of the
762 compiler generates a compiled form of your script whose executable is
763 just as big as the original perl executable, and then some. That's
764 because as currently written, all programs are prepared for a full
765 eval() statement. You can tremendously reduce this cost by building a
766 shared I<libperl.so> library and linking against that. See the
767 F<INSTALL> podfile in the Perl source distribution for details. If
768 you link your main perl binary with this, it will make it minuscule.
769 For example, on one author's system, F</usr/bin/perl> is only 11k in
772 In general, the compiler will do nothing to make a Perl program smaller,
773 faster, more portable, or more secure. In fact, it can make your
774 situation worse. The executable will be bigger, your VM system may take
775 longer to load the whole thing, the binary is fragile and hard to fix,
776 and compilation never stopped software piracy in the form of crackers,
777 viruses, or bootleggers. The real advantage of the compiler is merely
778 packaging, and once you see the size of what it makes (well, unless
779 you use a shared I<libperl.so>), you'll probably want a complete
782 =head2 How can I compile Perl into Java?
784 You can also integrate Java and Perl with the
785 Perl Resource Kit from O'Reilly and Associates. See
786 http://www.oreilly.com/catalog/prkunix/ .
788 Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in
789 development, allows Perl code to be called from Java. See jpl/README
790 in the Perl source tree.
792 =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
796 extproc perl -S -your_switches
798 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
799 `extproc' handling). For DOS one should first invent a corresponding
800 batch file and codify it in C<ALTERNATE_SHEBANG> (see the
801 F<dosish.h> file in the source distribution for more information).
803 The Win95/NT installation, when using the ActiveState port of Perl,
804 will modify the Registry to associate the C<.pl> extension with the
805 perl interpreter. If you install another port, perhaps even building
806 your own Win95/NT Perl from the standard sources by using a Windows port
807 of gcc (e.g., with cygwin or mingw32), then you'll have to modify
808 the Registry yourself. In addition to associating C<.pl> with the
809 interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them
810 run the program C<install-linux.pl> merely by typing C<install-linux>.
812 Macintosh Perl programs will have the appropriate Creator and
813 Type, so that double-clicking them will invoke the Perl application.
815 I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
816 throw the perl interpreter into your cgi-bin directory, in order to
817 get your programs working for a web server. This is an EXTREMELY big
818 security risk. Take the time to figure out how to do it correctly.
820 =head2 Can I write useful Perl programs on the command line?
822 Yes. Read L<perlrun> for more information. Some examples follow.
823 (These assume standard Unix shell quoting rules.)
825 # sum first and last fields
826 perl -lane 'print $F[0] + $F[-1]' *
828 # identify text files
829 perl -le 'for(@ARGV) {print if -f && -T _}' *
831 # remove (most) comments from C program
832 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
834 # make file a month younger than today, defeating reaper daemons
835 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
837 # find first unused uid
838 perl -le '$i++ while getpwuid($i); print $i'
840 # display reasonable manpath
841 echo $PATH | perl -nl -072 -e '
842 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
844 OK, the last one was actually an Obfuscated Perl Contest entry. :-)
846 =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system?
848 The problem is usually that the command interpreters on those systems
849 have rather different ideas about quoting than the Unix shells under
850 which the one-liners were created. On some systems, you may have to
851 change single-quotes to double ones, which you must I<NOT> do on Unix
852 or Plan9 systems. You might also have to change a single % to a %%.
857 perl -e 'print "Hello world\n"'
860 perl -e "print \"Hello world\n\""
863 print "Hello world\n"
864 (then Run "Myscript" or Shift-Command-R)
867 perl -e 'print "Hello world\n"'
870 perl -e "print ""Hello world\n"""
872 The problem is that none of these examples are reliable: they depend on the
873 command interpreter. Under Unix, the first two often work. Under DOS,
874 it's entirely possible that neither works. If 4DOS was the command shell,
875 you'd probably have better luck like this:
877 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
879 Under the Mac, it depends which environment you are using. The MacPerl
880 shell, or MPW, is much like Unix shells in its support for several
881 quoting variants, except that it makes free use of the Mac's non-ASCII
882 characters as control characters.
884 Using qq(), q(), and qx(), instead of "double quotes", 'single
885 quotes', and `backticks`, may make one-liners easier to write.
887 There is no general solution to all of this. It is a mess.
889 [Some of this answer was contributed by Kenneth Albanowski.]
891 =head2 Where can I learn about CGI or Web programming in Perl?
893 For modules, get the CGI or LWP modules from CPAN. For textbooks,
894 see the two especially dedicated to web stuff in the question on
895 books. For problems and questions related to the web, like ``Why
896 do I get 500 Errors'' or ``Why doesn't it run from the browser right
897 when it runs fine on the command line'', see the troubleshooting
898 guides and references in L<perlfaq9> or in the CGI MetaFAQ:
900 http://www.perl.org/CGI_MetaFAQ.html
902 =head2 Where can I learn about object-oriented Perl programming?
904 A good place to start is L<perltoot>, and you can use L<perlobj>,
905 L<perlboot>, L<perltoot>, L<perltooc>, and L<perlbot> for reference.
906 (If you are using really old Perl, you may not have all of these,
907 try http://www.perldoc.com/ , but consider upgrading your perl.)
909 A good book on OO on Perl is the "Object-Oriented Perl"
910 by Damian Conway from Manning Publications,
911 http://www.manning.com/Conway/index.html
913 =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp]
915 If you want to call C from Perl, start with L<perlxstut>,
916 moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to
917 call Perl from C, then read L<perlembed>, L<perlcall>, and
918 L<perlguts>. Don't forget that you can learn a lot from looking at
919 how the authors of existing extension modules wrote their code and
920 solved their problems.
922 =head2 I've read perlembed, perlguts, etc., but I can't embed perl in
923 my C program; what am I doing wrong?
925 Download the ExtUtils::Embed kit from CPAN and run `make test'. If
926 the tests pass, read the pods again and again and again. If they
927 fail, see L<perlbug> and send a bug report with the output of
928 C<make test TEST_VERBOSE=1> along with C<perl -V>.
930 =head2 When I tried to run my script, I got this message. What does it mean?
932 A complete list of Perl's error messages and warnings with explanatory
933 text can be found in L<perldiag>. You can also use the splain program
934 (distributed with Perl) to explain the error messages:
936 perl program 2>diag.out
937 splain [-v] [-p] diag.out
939 or change your program to explain the messages for you:
945 use diagnostics -verbose;
947 =head2 What's MakeMaker?
949 This module (part of the standard Perl distribution) is designed to
950 write a Makefile for an extension module from a Makefile.PL. For more
951 information, see L<ExtUtils::MakeMaker>.
953 =head1 AUTHOR AND COPYRIGHT
955 Copyright (c) 1997-2002 Tom Christiansen and Nathan Torkington.
958 This documentation is free; you can redistribute it and/or modify it
959 under the same terms as Perl itself.
961 Irrespective of its distribution, all code examples here are in the public
962 domain. You are permitted and encouraged to use this code and any
963 derivatives thereof in your own programs for fun or for profit as you
964 see fit. A simple comment in the code giving credit to the FAQ would
965 be courteous but is not required.