3 perlfaq3 - Programming Tools ($Revision: 1.29 $, $Date: 2002/11/13 06:23:50 $)
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 In general, not yet. There is psh available at
47 http://www.focusresearch.com/gregor/psh
49 Which includes the following description:
51 The Perl Shell is a shell that combines the interactive nature
52 of a Unix shell with the power of Perl. The goal is to eventually
53 have a full featured shell that behaves as expected for normal
54 shell activity. But, the Perl Shell will use Perl syntax and
55 functionality for control-flow statements and other things.
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 ``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 programs?''
480 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,
487 modules that have critical sections can be written in C (for instance, the
488 PDL module from CPAN).
490 In some cases, it may be worth it to use the backend compiler to
491 produce byte code (saving compilation time) or compile into C, which
492 will certainly save compilation time and sometimes a small amount (but
493 not much) execution time. See the question about compiling your Perl
494 programs for more on the compiler--the wins aren't as obvious as you'd
497 If you're currently linking your perl executable to a shared I<libc.so>,
498 you can often gain a 10-25% performance benefit by rebuilding it to
499 link with a static libc.a instead. This will make a bigger perl
500 executable, but your Perl programs (and programmers) may thank you for
501 it. See the F<INSTALL> file in the source distribution for more
504 Unsubstantiated reports allege that Perl interpreters that use sfio
505 outperform those that don't (for I/O intensive applications). To try
506 this, see the F<INSTALL> file in the source distribution, especially
507 the ``Selecting File I/O mechanisms'' section.
509 The undump program was an old attempt to speed up your Perl program
510 by storing the already-compiled form to disk. This is no longer
511 a viable option, as it only worked on a few architectures, and
512 wasn't a good solution anyway.
514 =head2 How can I make my Perl program take less memory?
516 When it comes to time-space tradeoffs, Perl nearly always prefers to
517 throw memory at a problem. Scalars in Perl use more memory than
518 strings in C, arrays take more than that, and hashes use even more. While
519 there's still a lot to be done, recent releases have been addressing
520 these issues. For example, as of 5.004, duplicate hash keys are
521 shared amongst all hashes using them, so require no reallocation.
523 In some cases, using substr() or vec() to simulate arrays can be
524 highly beneficial. For example, an array of a thousand booleans will
525 take at least 20,000 bytes of space, but it can be turned into one
526 125-byte bit vector--a considerable memory savings. The standard
527 Tie::SubstrHash module can also help for certain types of data
528 structure. If you're working with specialist data structures
529 (matrices, for instance) modules that implement these in C may use
530 less memory than equivalent Perl modules.
532 Another thing to try is learning whether your Perl was compiled with
533 the system malloc or with Perl's builtin malloc. Whichever one it
534 is, try using the other one and see whether this makes a difference.
535 Information about malloc is in the F<INSTALL> file in the source
536 distribution. You can find out whether you are using perl's malloc by
537 typing C<perl -V:usemymalloc>.
539 Of course, the best way to save memory is to not do anything to waste
540 it in the first place. Good programming practices can go a long way
547 Don't read an entire file into memory if you can process it line
548 by line. Or more concretely, use a loop like this:
567 When the files you're processing are small, it doesn't much matter which
568 way you do it, but it makes a huge difference when they start getting
571 =item * Use map and grep selectively
573 Remember that both map and grep expect a LIST argument, so doing this:
575 @wanted = grep {/pattern/} <FILE>;
577 will cause the entire file to be slurped. For large files, it's better
581 push(@wanted, $_) if /pattern/;
584 =item * Avoid unnecessary quotes and stringification
586 Don't quote large strings unless absolutely necessary:
588 my $copy = "$large_string";
590 makes 2 copies of $large_string (one for $copy and another for the
593 my $copy = $large_string;
597 Ditto for stringifying large arrays:
604 is much more memory-efficient than either
606 print join "\n", @big_array;
616 =item * Pass by reference
618 Pass arrays and hashes by reference, not by value. For one thing, it's
619 the only way to pass multiple lists or hashes (or both) in a single
620 call/return. It also avoids creating a copy of all the contents. This
621 requires some judgment, however, because any changes will be propagated
622 back to the original data. If you really want to mangle (er, modify) a
623 copy, you'll have to sacrifice the memory needed to make one.
625 =item * Tie large variables to disk.
627 For "big" data stores (i.e. ones that exceed available memory) consider
628 using one of the DB modules to store it on disk instead of in RAM. This
629 will incur a penalty in access time, but that's probably better than
630 causing your hard disk to thrash due to massive swapping.
634 =head2 Is it safe to return a reference to local or lexical data?
636 Yes. Perl's garbage collection system takes care of this so
637 everything works out right.
645 push @many, makeone();
648 print $many[4][5], "\n";
652 =head2 How can I free an array or hash so my program shrinks?
654 You usually can't. On most operating systems, memory
655 allocated to a program can never be returned to the system.
656 That's why long-running programs sometimes re-exec
657 themselves. Some operating systems (notably, systems that
658 use mmap(2) for allocating large chunks of memory) can
659 reclaim memory that is no longer used, but on such systems,
660 perl must be configured and compiled to use the OS's malloc,
663 However, judicious use of my() on your variables will help make sure
664 that they go out of scope so that Perl can free up that space for
665 use in other parts of your program. A global variable, of course, never
666 goes out of scope, so you can't get its space automatically reclaimed,
667 although undef()ing and/or delete()ing it will achieve the same effect.
668 In general, memory allocation and de-allocation isn't something you can
669 or should be worrying about much in Perl, but even this capability
670 (preallocation of data types) is in the works.
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 Malcolm Beattie has written a multifunction backend compiler,
759 available from CPAN, that can do both these things. It is included
760 in the perl5.005 release, but is still considered experimental.
761 This means it's fun to play with if you're a programmer but not
762 really for people looking for turn-key solutions.
764 Merely compiling into C does not in and of itself guarantee that your
765 code will run very much faster. That's because except for lucky cases
766 where a lot of native type inferencing is possible, the normal Perl
767 run-time system is still present and so your program will take just as
768 long to run and be just as big. Most programs save little more than
769 compilation time, leaving execution no more than 10-30% faster. A few
770 rare programs actually benefit significantly (even running several times
771 faster), but this takes some tweaking of your code.
773 You'll probably be astonished to learn that the current version of the
774 compiler generates a compiled form of your script whose executable is
775 just as big as the original perl executable, and then some. That's
776 because as currently written, all programs are prepared for a full
777 eval() statement. You can tremendously reduce this cost by building a
778 shared I<libperl.so> library and linking against that. See the
779 F<INSTALL> podfile in the Perl source distribution for details. If
780 you link your main perl binary with this, it will make it minuscule.
781 For example, on one author's system, F</usr/bin/perl> is only 11k in
784 In general, the compiler will do nothing to make a Perl program smaller,
785 faster, more portable, or more secure. In fact, it can make your
786 situation worse. The executable will be bigger, your VM system may take
787 longer to load the whole thing, the binary is fragile and hard to fix,
788 and compilation never stopped software piracy in the form of crackers,
789 viruses, or bootleggers. The real advantage of the compiler is merely
790 packaging, and once you see the size of what it makes (well, unless
791 you use a shared I<libperl.so>), you'll probably want a complete
794 =head2 How can I compile Perl into Java?
796 You can also integrate Java and Perl with the
797 Perl Resource Kit from O'Reilly and Associates. See
798 http://www.oreilly.com/catalog/prkunix/ .
800 Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in
801 development, allows Perl code to be called from Java. See jpl/README
802 in the Perl source tree.
804 =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
808 extproc perl -S -your_switches
810 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
811 `extproc' handling). For DOS one should first invent a corresponding
812 batch file and codify it in C<ALTERNATIVE_SHEBANG> (see the
813 F<INSTALL> file in the source distribution for more information).
815 The Win95/NT installation, when using the ActiveState port of Perl,
816 will modify the Registry to associate the C<.pl> extension with the
817 perl interpreter. If you install another port, perhaps even building
818 your own Win95/NT Perl from the standard sources by using a Windows port
819 of gcc (e.g., with cygwin or mingw32), then you'll have to modify
820 the Registry yourself. In addition to associating C<.pl> with the
821 interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them
822 run the program C<install-linux.pl> merely by typing C<install-linux>.
824 Macintosh Perl programs will have the appropriate Creator and
825 Type, so that double-clicking them will invoke the Perl application.
827 I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
828 throw the perl interpreter into your cgi-bin directory, in order to
829 get your programs working for a web server. This is an EXTREMELY big
830 security risk. Take the time to figure out how to do it correctly.
832 =head2 Can I write useful Perl programs on the command line?
834 Yes. Read L<perlrun> for more information. Some examples follow.
835 (These assume standard Unix shell quoting rules.)
837 # sum first and last fields
838 perl -lane 'print $F[0] + $F[-1]' *
840 # identify text files
841 perl -le 'for(@ARGV) {print if -f && -T _}' *
843 # remove (most) comments from C program
844 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
846 # make file a month younger than today, defeating reaper daemons
847 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
849 # find first unused uid
850 perl -le '$i++ while getpwuid($i); print $i'
852 # display reasonable manpath
853 echo $PATH | perl -nl -072 -e '
854 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
856 OK, the last one was actually an Obfuscated Perl Contest entry. :-)
858 =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system?
860 The problem is usually that the command interpreters on those systems
861 have rather different ideas about quoting than the Unix shells under
862 which the one-liners were created. On some systems, you may have to
863 change single-quotes to double ones, which you must I<NOT> do on Unix
864 or Plan9 systems. You might also have to change a single % to a %%.
869 perl -e 'print "Hello world\n"'
872 perl -e "print \"Hello world\n\""
875 print "Hello world\n"
876 (then Run "Myscript" or Shift-Command-R)
879 perl -e 'print "Hello world\n"'
882 perl -e "print ""Hello world\n"""
884 The problem is that none of these examples are reliable: they depend on the
885 command interpreter. Under Unix, the first two often work. Under DOS,
886 it's entirely possible that neither works. If 4DOS was the command shell,
887 you'd probably have better luck like this:
889 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
891 Under the Mac, it depends which environment you are using. The MacPerl
892 shell, or MPW, is much like Unix shells in its support for several
893 quoting variants, except that it makes free use of the Mac's non-ASCII
894 characters as control characters.
896 Using qq(), q(), and qx(), instead of "double quotes", 'single
897 quotes', and `backticks`, may make one-liners easier to write.
899 There is no general solution to all of this. It is a mess.
901 [Some of this answer was contributed by Kenneth Albanowski.]
903 =head2 Where can I learn about CGI or Web programming in Perl?
905 For modules, get the CGI or LWP modules from CPAN. For textbooks,
906 see the two especially dedicated to web stuff in the question on
907 books. For problems and questions related to the web, like ``Why
908 do I get 500 Errors'' or ``Why doesn't it run from the browser right
909 when it runs fine on the command line'', see the troubleshooting
910 guides and references in L<perlfaq9> or in the CGI MetaFAQ:
912 http://www.perl.org/CGI_MetaFAQ.html
914 =head2 Where can I learn about object-oriented Perl programming?
916 A good place to start is L<perltoot>, and you can use L<perlobj>,
917 L<perlboot>, L<perltoot>, L<perltooc>, and L<perlbot> for reference.
918 (If you are using really old Perl, you may not have all of these,
919 try http://www.perldoc.com/ , but consider upgrading your perl.)
921 A good book on OO on Perl is the "Object-Oriented Perl"
922 by Damian Conway from Manning Publications,
923 http://www.manning.com/Conway/index.html
925 =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp]
927 If you want to call C from Perl, start with L<perlxstut>,
928 moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to
929 call Perl from C, then read L<perlembed>, L<perlcall>, and
930 L<perlguts>. Don't forget that you can learn a lot from looking at
931 how the authors of existing extension modules wrote their code and
932 solved their problems.
934 =head2 I've read perlembed, perlguts, etc., but I can't embed perl in
935 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) 1997-2002 Tom Christiansen and Nathan Torkington.
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.