3 perlfaq3 - Programming Tools ($Revision: 1.22 $, $Date: 2002/05/06 13:11:13 $)
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 debug my Perl programs?
64 Have you tried C<use warnings> or used C<-w>? They enable warnings
65 to detect dubious practices.
67 Have you tried C<use strict>? It prevents you from using symbolic
68 references, makes you predeclare any subroutines that you call as bare
69 words, and (probably most importantly) forces you to predeclare your
70 variables with C<my>, C<our>, or C<use vars>.
72 Did you check the return values of each and every system call? The operating
73 system (and thus Perl) tells you whether they worked, and if not
76 open(FH, "> /etc/cantwrite")
77 or die "Couldn't write to /etc/cantwrite: $!\n";
79 Did you read L<perltrap>? It's full of gotchas for old and new Perl
80 programmers and even has sections for those of you who are upgrading
81 from languages like I<awk> and I<C>.
83 Have you tried the Perl debugger, described in L<perldebug>? You can
84 step through your program and see what it's doing and thus work out
85 why what it's doing isn't what it should be doing.
87 =head2 How do I profile my Perl programs?
89 You should get the Devel::DProf module from the standard distribution
90 (or separately on CPAN) and also use Benchmark.pm from the standard
91 distribution. The Benchmark module lets you time specific portions of
92 your code, while Devel::DProf gives detailed breakdowns of where your
95 Here's a sample use of Benchmark:
99 @junk = `cat /etc/motd`;
103 'map' => sub { my @a = @junk;
107 'for' => sub { my @a = @junk;
113 This is what it prints (on one machine--your results will be dependent
114 on your hardware, operating system, and the load on your machine):
116 Benchmark: timing 10000 iterations of for, map...
117 for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu)
118 map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu)
120 Be aware that a good benchmark is very hard to write. It only tests the
121 data you give it and proves little about the differing complexities
122 of contrasting algorithms.
124 =head2 How do I cross-reference my Perl programs?
126 The B::Xref module can be used to generate cross-reference reports
129 perl -MO=Xref[,OPTIONS] scriptname.plx
131 =head2 Is there a pretty-printer (formatter) for Perl?
133 Perltidy is a Perl script which indents and reformats Perl scripts
134 to make them easier to read by trying to follow the rules of the
135 L<perlstyle>. If you write Perl scripts, or spend much time reading
136 them, you will probably find it useful. It is available at
137 http://perltidy.sourceforge.net
139 Of course, if you simply follow the guidelines in L<perlstyle>,
140 you shouldn't need to reformat. The habit of formatting your code
141 as you write it will help prevent bugs. Your editor can and should
142 help you with this. The perl-mode or newer cperl-mode for emacs
143 can provide remarkable amounts of help with most (but not all)
144 code, and even less programmable editors can provide significant
145 assistance. Tom Christiansen and many other VI users swear by
146 the following settings in vi and its clones:
151 Put that in your F<.exrc> file (replacing the caret characters
152 with control characters) and away you go. In insert mode, ^T is
153 for indenting, ^D is for undenting, and ^O is for blockdenting--
154 as it were. A more complete example, with comments, can be found at
155 http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz
157 The a2ps http://www-inf.enst.fr/%7Edemaille/a2ps/black+white.ps does
158 lots of things related to generating nicely printed output of
159 documents, as does enscript at http://people.ssh.fi/mtr/genscript/ .
161 =head2 Is there a ctags for Perl?
163 Recent versions of ctags do much more than older versions did.
164 EXUBERANT CTAGS is available from http://ctags.sourceforge.net/
165 and does a good job of making tags files for perl code.
167 There is also a simple one at
168 http://www.cpan.org/authors/id/TOMC/scripts/ptags.gz which may do
169 the trick. It can be easy to hack this into what you want.
171 =head2 Is there an IDE or Windows Perl Editor?
173 Perl programs are just plain text, so any editor will do.
175 If you're on Unix, you already have an IDE--Unix itself. The UNIX
176 philosophy is the philosophy of several small tools that each do one
177 thing and do it well. It's like a carpenter's toolbox.
179 If you want an IDE, check the following:
185 ActiveState's cross-platform (as of April 2001 Windows and Linux),
186 multi-language IDE has Perl support, including a regular expression
187 debugger and remote debugging
188 ( http://www.ActiveState.com/Products/Komodo/index.html ). (Visual
189 Perl, a Visual Studio.NET plug-in is currently (early 2001) in beta
190 ( http://www.ActiveState.com/Products/VisualPerl/index.html )).
192 =item The Object System
194 ( http://www.castlelink.co.uk/object_system/ ) is a Perl web
195 applications development IDE, apparently for any platform
200 ( http://open-perl-ide.sourceforge.net/ )
201 Open Perl IDE is an integrated development environment for writing
202 and debugging Perl scripts with ActiveState's ActivePerl distribution
203 under Windows 95/98/NT/2000.
207 ( http://www.solutionsoft.com/perl.htm ) is an integrated development
208 environment for Windows that supports Perl development.
212 ( http://helpconsulting.net/visiperl/ )
213 From Help Consulting, for Windows.
217 ( http://www.optiperl.com/ ) is a Windows IDE with simulated CGI
218 environment, including debugger and syntax highlighting editor.
222 For Windows there's also the
228 ( http://www.codemagiccd.com/ ) Collection of various programming
229 tools for Windows: Perl (5.005_03), TclTk, Python, GNU programming
230 tools, REBOL, wxWindows toolkit, the MinGW GNU C/C++ compiler, DJGPP
231 GNU C/C++ compiler, Cint C interpreter, YaBasic.
235 For editors: if you're on Unix you probably have vi or a vi clone already,
236 and possibly an emacs too, so you may not need to download anything.
237 In any emacs the cperl-mode (M-x cperl-mode) gives you perhaps the
238 best available Perl editing mode in any editor.
240 If you are using Windows, you can use any editor that lets
241 you work with plain text, such as NotePad or WordPad. Word
242 processors, such as Microsoft Word or WordPerfect, typically
243 do not work since they insert all sorts of behind-the-scenes
244 information, although some allow you to save files as "Text
245 Only". You can also download text editors designed
246 specifically for programming, such as Textpad
247 ( http://www.textpad.com/ ) and UltraEdit
248 ( http://www.ultraedit.com/ ), among others.
250 If you are using MacOS, the same concerns apply. MacPerl
251 (for Classic environments) comes with a simple editor.
252 Popular external editors are BBEdit ( http://www.bbedit.com/ )
253 or Alpha ( http://www.kelehers.org/alpha/ ). MacOS X users can
254 use Unix editors as well.
260 http://www.gnu.org/software/emacs/windows/ntemacs.html
264 http://members.nbci.com/uemacs/
268 http://www.xemacs.org/Download/index.html
272 or a vi clone such as
278 ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/
288 win32: http://www.cs.vu.nl/%7Etmgil/vi.html
292 For vi lovers in general, Windows or elsewhere:
294 http://www.thomer.com/thomer/vi/vi.html
296 nvi ( http://www.bostic.com/vi/ , available from CPAN in src/misc/) is
297 yet another vi clone, unfortunately not available for Windows, but in
298 UNIX platforms you might be interested in trying it out, firstly because
299 strictly speaking it is not a vi clone, it is the real vi, or the new
300 incarnation of it, and secondly because you can embed Perl inside it
301 to use Perl as the scripting language. nvi is not alone in this,
302 though: at least also vim and vile offer an embedded Perl.
304 The following are Win32 multilanguage editor/IDESs that support Perl:
310 http://www.starbase.com/
314 http://www.MultiEdit.com/
318 http://www.slickedit.com/
322 There is also a toyedit Text widget based editor written in Perl
323 that is distributed with the Tk module on CPAN. The ptkdb
324 ( http://world.std.com/~aep/ptkdb/ ) is a Perl/tk based debugger that
325 acts as a development environment of sorts. Perl Composer
326 ( http://perlcomposer.sourceforge.net/vperl.html ) is an IDE for Perl/Tk
329 In addition to an editor/IDE you might be interested in a more
330 powerful shell environment for Win32. Your options include
336 from the Cygwin package ( http://sources.redhat.com/cygwin/ )
340 from the MKS Toolkit ( http://www.mks.com/ ), or the Bourne shell of
341 the U/WIN environment ( http://www.research.att.com/sw/tools/uwin/ )
345 ftp://ftp.astron.com/pub/tcsh/ , see also
346 http://www.primate.wisc.edu/software/csh-tcsh-book/
350 ftp://ftp.blarg.net/users/amol/zsh/ , see also http://www.zsh.org/
354 MKS and U/WIN are commercial (U/WIN is free for educational and
355 research purposes), Cygwin is covered by the GNU Public License (but
356 that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all
357 contain (in addition to the shells) a comprehensive set of standard
358 UNIX toolkit utilities.
360 If you're transferring text files between Unix and Windows using FTP
361 be sure to transfer them in ASCII mode so the ends of lines are
362 appropriately converted.
364 On Mac OS the MacPerl Application comes with a simple 32k text editor
365 that behaves like a rudimentary IDE. In contrast to the MacPerl Application
366 the MPW Perl tool can make use of the MPW Shell itself as an editor (with
371 =item BBEdit and BBEdit Lite
373 are text editors for Mac OS that have a Perl sensitivity mode
374 ( http://web.barebones.com/ ).
378 is an editor, written and extensible in Tcl, that nonetheless has
379 built in support for several popular markup and programming languages
380 including Perl and HTML ( http://alpha.olm.net/ ).
384 Pepper and Pe are programming language sensitive text editors for Mac
385 OS X and BeOS respectively ( http://www.hekkelman.com/ ).
387 =head2 Where can I get Perl macros for vi?
389 For a complete version of Tom Christiansen's vi configuration file,
390 see http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz ,
391 the standard benchmark file for vi emulators. The file runs best with nvi,
392 the current version of vi out of Berkeley, which incidentally can be built
393 with an embedded Perl interpreter--see http://www.cpan.org/src/misc/ .
395 =head2 Where can I get perl-mode for emacs?
397 Since Emacs version 19 patchlevel 22 or so, there have been both a
398 perl-mode.el and support for the Perl debugger built in. These should
399 come with the standard Emacs 19 distribution.
401 In the Perl source directory, you'll find a directory called "emacs",
402 which contains a cperl-mode that color-codes keywords, provides
403 context-sensitive help, and other nifty things.
405 Note that the perl-mode of emacs will have fits with C<"main'foo">
406 (single quote), and mess up the indentation and highlighting. You
407 are probably using C<"main::foo"> in new Perl code anyway, so this
408 shouldn't be an issue.
410 =head2 How can I use curses with Perl?
412 The Curses module from CPAN provides a dynamically loadable object
413 module interface to a curses library. A small demo can be found at the
414 directory http://www.cpan.org/authors/Tom_Christiansen/scripts/rep ;
415 this program repeats a command and updates the screen as needed, rendering
416 B<rep ps axu> similar to B<top>.
418 =head2 How can I use X or Tk with Perl?
420 Tk is a completely Perl-based, object-oriented interface to the Tk toolkit
421 that doesn't force you to use Tcl just to get at Tk. Sx is an interface
422 to the Athena Widget set. Both are available from CPAN. See the
423 directory http://www.cpan.org/modules/by-category/08_User_Interfaces/
425 Invaluable for Perl/Tk programming are the Perl/Tk FAQ at
426 http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference
428 http://www.cpan.org/authors/Stephen_O_Lidie/ , and the
430 http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html .
432 =head2 How can I generate simple menus without using CGI or Tk?
434 The http://www.cpan.org/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
435 module, which is curses-based, can help with this.
437 =head2 How can I make my Perl program run faster?
439 The best way to do this is to come up with a better algorithm. This
440 can often make a dramatic difference. Jon Bentley's book
441 ``Programming Pearls'' (that's not a misspelling!) has some good tips
442 on optimization, too. Advice on benchmarking boils down to: benchmark
443 and profile to make sure you're optimizing the right part, look for
444 better algorithms instead of microtuning your code, and when all else
445 fails consider just buying faster hardware. You will probably want to
446 read the answer to the earlier question ``How do I profile my Perl programs?''
447 if you haven't done so already.
449 A different approach is to autoload seldom-used Perl code. See the
450 AutoSplit and AutoLoader modules in the standard distribution for
451 that. Or you could locate the bottleneck and think about writing just
452 that part in C, the way we used to take bottlenecks in C code and
453 write them in assembler. Similar to rewriting in C,
454 modules that have critical sections can be written in C (for instance, the
455 PDL module from CPAN).
457 In some cases, it may be worth it to use the backend compiler to
458 produce byte code (saving compilation time) or compile into C, which
459 will certainly save compilation time and sometimes a small amount (but
460 not much) execution time. See the question about compiling your Perl
461 programs for more on the compiler--the wins aren't as obvious as you'd
464 If you're currently linking your perl executable to a shared I<libc.so>,
465 you can often gain a 10-25% performance benefit by rebuilding it to
466 link with a static libc.a instead. This will make a bigger perl
467 executable, but your Perl programs (and programmers) may thank you for
468 it. See the F<INSTALL> file in the source distribution for more
471 Unsubstantiated reports allege that Perl interpreters that use sfio
472 outperform those that don't (for I/O intensive applications). To try
473 this, see the F<INSTALL> file in the source distribution, especially
474 the ``Selecting File I/O mechanisms'' section.
476 The undump program was an old attempt to speed up your Perl program
477 by storing the already-compiled form to disk. This is no longer
478 a viable option, as it only worked on a few architectures, and
479 wasn't a good solution anyway.
481 =head2 How can I make my Perl program take less memory?
483 When it comes to time-space tradeoffs, Perl nearly always prefers to
484 throw memory at a problem. Scalars in Perl use more memory than
485 strings in C, arrays take more than that, and hashes use even more. While
486 there's still a lot to be done, recent releases have been addressing
487 these issues. For example, as of 5.004, duplicate hash keys are
488 shared amongst all hashes using them, so require no reallocation.
490 In some cases, using substr() or vec() to simulate arrays can be
491 highly beneficial. For example, an array of a thousand booleans will
492 take at least 20,000 bytes of space, but it can be turned into one
493 125-byte bit vector--a considerable memory savings. The standard
494 Tie::SubstrHash module can also help for certain types of data
495 structure. If you're working with specialist data structures
496 (matrices, for instance) modules that implement these in C may use
497 less memory than equivalent Perl modules.
499 Another thing to try is learning whether your Perl was compiled with
500 the system malloc or with Perl's builtin malloc. Whichever one it
501 is, try using the other one and see whether this makes a difference.
502 Information about malloc is in the F<INSTALL> file in the source
503 distribution. You can find out whether you are using perl's malloc by
504 typing C<perl -V:usemymalloc>.
506 Of course, the best way to save memory is to not do anything to waste
507 it in the first place. Good programming practices can go a long way
514 Don't read an entire file into memory if you can process it line
515 by line. Or more concretely, use a loop like this:
534 When the files you're processing are small, it doesn't much matter which
535 way you do it, but it makes a huge difference when they start getting
538 =item * Use map and grep selectively
540 Remember that both map and grep expect a LIST argument, so doing this:
542 @wanted = grep {/pattern/} <FILE>;
544 will cause the entire file to be slurped. For large files, it's better
548 push(@wanted, $_) if /pattern/;
551 =item * Avoid unnecessary quotes and stringification
553 Don't quote large strings unless absolutely necessary:
555 my $copy = "$large_string";
557 makes 2 copies of $large_string (one for $copy and another for the
560 my $copy = $large_string;
564 Ditto for stringifying large arrays:
571 is much more memory-efficient than either
573 print join "\n", @big_array;
583 =item * Pass by reference
585 Pass arrays and hashes by reference, not by value. For one thing, it's
586 the only way to pass multiple lists or hashes (or both) in a single
587 call/return. It also avoids creating a copy of all the contents. This
588 requires some judgment, however, because any changes will be propagated
589 back to the original data. If you really want to mangle (er, modify) a
590 copy, you'll have to sacrifice the memory needed to make one.
592 =item * Tie large variables to disk.
594 For "big" data stores (i.e. ones that exceed available memory) consider
595 using one of the DB modules to store it on disk instead of in RAM. This
596 will incur a penalty in access time, but that's probably better than
597 causing your hard disk to thrash due to massive swapping.
601 =head2 Is it unsafe to return a pointer to local data?
603 No, Perl's garbage collection system takes care of this.
611 push @many, makeone();
614 print $many[4][5], "\n";
618 =head2 How can I free an array or hash so my program shrinks?
620 You usually can't. On most operating systems, memory
621 allocated to a program can never be returned to the system.
622 That's why long-running programs sometimes re-exec
623 themselves. Some operating systems (notably, systems that
624 use mmap(2) for allocating large chunks of memory) can
625 reclaim memory that is no longer used, but on such systems,
626 perl must be configured and compiled to use the OS's malloc,
629 However, judicious use of my() on your variables will help make sure
630 that they go out of scope so that Perl can free up that space for
631 use in other parts of your program. A global variable, of course, never
632 goes out of scope, so you can't get its space automatically reclaimed,
633 although undef()ing and/or delete()ing it will achieve the same effect.
634 In general, memory allocation and de-allocation isn't something you can
635 or should be worrying about much in Perl, but even this capability
636 (preallocation of data types) is in the works.
638 =head2 How can I make my CGI script more efficient?
640 Beyond the normal measures described to make general Perl programs
641 faster or smaller, a CGI program has additional issues. It may be run
642 several times per second. Given that each time it runs it will need
643 to be re-compiled and will often allocate a megabyte or more of system
644 memory, this can be a killer. Compiling into C B<isn't going to help
645 you> because the process start-up overhead is where the bottleneck is.
647 There are two popular ways to avoid this overhead. One solution
648 involves running the Apache HTTP server (available from
649 http://www.apache.org/ ) with either of the mod_perl or mod_fastcgi
652 With mod_perl and the Apache::Registry module (distributed with
653 mod_perl), httpd will run with an embedded Perl interpreter which
654 pre-compiles your script and then executes it within the same address
655 space without forking. The Apache extension also gives Perl access to
656 the internal server API, so modules written in Perl can do just about
657 anything a module written in C can. For more on mod_perl, see
658 http://perl.apache.org/
660 With the FCGI module (from CPAN) and the mod_fastcgi
661 module (available from http://www.fastcgi.com/ ) each of your Perl
662 programs becomes a permanent CGI daemon process.
664 Both of these solutions can have far-reaching effects on your system
665 and on the way you write your CGI programs, so investigate them with
668 See http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
670 A non-free, commercial product, ``The Velocity Engine for Perl'',
671 (http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ )
672 might also be worth looking at. It will allow you to increase the
673 performance of your Perl programs, running programs up to 25 times
674 faster than normal CGI Perl when running in persistent Perl mode or 4
675 to 5 times faster without any modification to your existing CGI
676 programs. Fully functional evaluation copies are available from the
679 =head2 How can I hide the source for my Perl program?
681 Delete it. :-) Seriously, there are a number of (mostly
682 unsatisfactory) solutions with varying levels of ``security''.
684 First of all, however, you I<can't> take away read permission, because
685 the source code has to be readable in order to be compiled and
686 interpreted. (That doesn't mean that a CGI script's source is
687 readable by people on the web, though--only by people with access to
688 the filesystem.) So you have to leave the permissions at the socially
691 Some people regard this as a security problem. If your program does
692 insecure things and relies on people not knowing how to exploit those
693 insecurities, it is not secure. It is often possible for someone to
694 determine the insecure things and exploit them without viewing the
695 source. Security through obscurity, the name for hiding your bugs
696 instead of fixing them, is little security indeed.
698 You can try using encryption via source filters (Starting from Perl
699 5.8 the Filter::Simple and Filter::Util::Call modules are included in
700 the standard distribution), but any decent programmer will be able to
701 decrypt it. You can try using the byte code compiler and interpreter
702 described below, but the curious might still be able to de-compile it.
703 You can try using the native-code compiler described below, but
704 crackers might be able to disassemble it. These pose varying degrees
705 of difficulty to people wanting to get at your code, but none can
706 definitively conceal it (true of every language, not just Perl).
708 If you're concerned about people profiting from your code, then the
709 bottom line is that nothing but a restrictive license will give you
710 legal security. License your software and pepper it with threatening
711 statements like ``This is unpublished proprietary software of XYZ Corp.
712 Your access to it does not give you permission to use it blah blah
713 blah.'' We are not lawyers, of course, so you should see a lawyer if
714 you want to be sure your license's wording will stand up in court.
716 =head2 How can I compile my Perl program into byte code or C?
718 Malcolm Beattie has written a multifunction backend compiler,
719 available from CPAN, that can do both these things. It is included
720 in the perl5.005 release, but is still considered experimental.
721 This means it's fun to play with if you're a programmer but not
722 really for people looking for turn-key solutions.
724 Merely compiling into C does not in and of itself guarantee that your
725 code will run very much faster. That's because except for lucky cases
726 where a lot of native type inferencing is possible, the normal Perl
727 run-time system is still present and so your program will take just as
728 long to run and be just as big. Most programs save little more than
729 compilation time, leaving execution no more than 10-30% faster. A few
730 rare programs actually benefit significantly (even running several times
731 faster), but this takes some tweaking of your code.
733 You'll probably be astonished to learn that the current version of the
734 compiler generates a compiled form of your script whose executable is
735 just as big as the original perl executable, and then some. That's
736 because as currently written, all programs are prepared for a full
737 eval() statement. You can tremendously reduce this cost by building a
738 shared I<libperl.so> library and linking against that. See the
739 F<INSTALL> podfile in the Perl source distribution for details. If
740 you link your main perl binary with this, it will make it minuscule.
741 For example, on one author's system, F</usr/bin/perl> is only 11k in
744 In general, the compiler will do nothing to make a Perl program smaller,
745 faster, more portable, or more secure. In fact, it can make your
746 situation worse. The executable will be bigger, your VM system may take
747 longer to load the whole thing, the binary is fragile and hard to fix,
748 and compilation never stopped software piracy in the form of crackers,
749 viruses, or bootleggers. The real advantage of the compiler is merely
750 packaging, and once you see the size of what it makes (well, unless
751 you use a shared I<libperl.so>), you'll probably want a complete
754 =head2 How can I compile Perl into Java?
756 You can also integrate Java and Perl with the
757 Perl Resource Kit from O'Reilly and Associates. See
758 http://www.oreilly.com/catalog/prkunix/ .
760 Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in
761 development, allows Perl code to be called from Java. See jpl/README
762 in the Perl source tree.
764 =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
768 extproc perl -S -your_switches
770 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
771 `extproc' handling). For DOS one should first invent a corresponding
772 batch file and codify it in C<ALTERNATIVE_SHEBANG> (see the
773 F<INSTALL> file in the source distribution for more information).
775 The Win95/NT installation, when using the ActiveState port of Perl,
776 will modify the Registry to associate the C<.pl> extension with the
777 perl interpreter. If you install another port, perhaps even building
778 your own Win95/NT Perl from the standard sources by using a Windows port
779 of gcc (e.g., with cygwin or mingw32), then you'll have to modify
780 the Registry yourself. In addition to associating C<.pl> with the
781 interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them
782 run the program C<install-linux.pl> merely by typing C<install-linux>.
784 Macintosh Perl programs will have the appropriate Creator and
785 Type, so that double-clicking them will invoke the Perl application.
787 I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
788 throw the perl interpreter into your cgi-bin directory, in order to
789 get your programs working for a web server. This is an EXTREMELY big
790 security risk. Take the time to figure out how to do it correctly.
792 =head2 Can I write useful Perl programs on the command line?
794 Yes. Read L<perlrun> for more information. Some examples follow.
795 (These assume standard Unix shell quoting rules.)
797 # sum first and last fields
798 perl -lane 'print $F[0] + $F[-1]' *
800 # identify text files
801 perl -le 'for(@ARGV) {print if -f && -T _}' *
803 # remove (most) comments from C program
804 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
806 # make file a month younger than today, defeating reaper daemons
807 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
809 # find first unused uid
810 perl -le '$i++ while getpwuid($i); print $i'
812 # display reasonable manpath
813 echo $PATH | perl -nl -072 -e '
814 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
816 OK, the last one was actually an Obfuscated Perl Contest entry. :-)
818 =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system?
820 The problem is usually that the command interpreters on those systems
821 have rather different ideas about quoting than the Unix shells under
822 which the one-liners were created. On some systems, you may have to
823 change single-quotes to double ones, which you must I<NOT> do on Unix
824 or Plan9 systems. You might also have to change a single % to a %%.
829 perl -e 'print "Hello world\n"'
832 perl -e "print \"Hello world\n\""
835 print "Hello world\n"
836 (then Run "Myscript" or Shift-Command-R)
839 perl -e 'print "Hello world\n"'
842 perl -e "print ""Hello world\n"""
844 The problem is that none of these examples are reliable: they depend on the
845 command interpreter. Under Unix, the first two often work. Under DOS,
846 it's entirely possible that neither works. If 4DOS was the command shell,
847 you'd probably have better luck like this:
849 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
851 Under the Mac, it depends which environment you are using. The MacPerl
852 shell, or MPW, is much like Unix shells in its support for several
853 quoting variants, except that it makes free use of the Mac's non-ASCII
854 characters as control characters.
856 Using qq(), q(), and qx(), instead of "double quotes", 'single
857 quotes', and `backticks`, may make one-liners easier to write.
859 There is no general solution to all of this. It is a mess.
861 [Some of this answer was contributed by Kenneth Albanowski.]
863 =head2 Where can I learn about CGI or Web programming in Perl?
865 For modules, get the CGI or LWP modules from CPAN. For textbooks,
866 see the two especially dedicated to web stuff in the question on
867 books. For problems and questions related to the web, like ``Why
868 do I get 500 Errors'' or ``Why doesn't it run from the browser right
869 when it runs fine on the command line'', see the troubleshooting
870 guides and references in L<perlfaq9> or in the CGI MetaFAQ:
872 http://www.perl.org/CGI_MetaFAQ.html
874 =head2 Where can I learn about object-oriented Perl programming?
876 A good place to start is L<perltoot>, and you can use L<perlobj>,
877 L<perlboot>, L<perltoot>, L<perltooc>, and L<perlbot> for reference.
878 (If you are using really old Perl, you may not have all of these,
879 try http://www.perldoc.com/ , but consider upgrading your perl.)
881 A good book on OO on Perl is the "Object-Oriented Perl"
882 by Damian Conway from Manning Publications,
883 http://www.manning.com/Conway/index.html
885 =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp]
887 If you want to call C from Perl, start with L<perlxstut>,
888 moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to
889 call Perl from C, then read L<perlembed>, L<perlcall>, and
890 L<perlguts>. Don't forget that you can learn a lot from looking at
891 how the authors of existing extension modules wrote their code and
892 solved their problems.
894 =head2 I've read perlembed, perlguts, etc., but I can't embed perl in
895 my C program; what am I doing wrong?
897 Download the ExtUtils::Embed kit from CPAN and run `make test'. If
898 the tests pass, read the pods again and again and again. If they
899 fail, see L<perlbug> and send a bug report with the output of
900 C<make test TEST_VERBOSE=1> along with C<perl -V>.
902 =head2 When I tried to run my script, I got this message. What does it mean?
904 A complete list of Perl's error messages and warnings with explanatory
905 text can be found in L<perldiag>. You can also use the splain program
906 (distributed with Perl) to explain the error messages:
908 perl program 2>diag.out
909 splain [-v] [-p] diag.out
911 or change your program to explain the messages for you:
917 use diagnostics -verbose;
919 =head2 What's MakeMaker?
921 This module (part of the standard Perl distribution) is designed to
922 write a Makefile for an extension module from a Makefile.PL. For more
923 information, see L<ExtUtils::MakeMaker>.
925 =head1 AUTHOR AND COPYRIGHT
927 Copyright (c) 1997-2002 Tom Christiansen and Nathan Torkington.
930 This documentation is free; you can redistribute it and/or modify it
931 under the same terms as Perl itself.
933 Irrespective of its distribution, all code examples here are in the public
934 domain. You are permitted and encouraged to use this code and any
935 derivatives thereof in your own programs for fun or for profit as you
936 see fit. A simple comment in the code giving credit to the FAQ would
937 be courteous but is not required.