3 perlfaq3 - Programming Tools ($Revision: 1.18 $, $Date: 2002/04/09 17:11:16 $)
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 For Windows there's also the
223 ( http://www.codemagiccd.com/ ) Collection of various programming
224 tools for Windows: Perl (5.005_03), TclTk, Python, GNU programming
225 tools, REBOL, wxWindows toolkit, the MinGW GNU C/C++ compiler, DJGPP
226 GNU C/C++ compiler, Cint C interpreter, YaBasic.
230 For editors: if you're on Unix you probably have vi or a vi clone already,
231 and possibly an emacs too, so you may not need to download anything.
232 In any emacs the cperl-mode (M-x cperl-mode) gives you perhaps the
233 best available Perl editing mode in any editor.
235 If you are using Windows, you can use any editor that lets
236 you work with plain text, such as NotePad or WordPad. Word
237 processors, such as Microsoft Word or WordPerfect, typically
238 do not work since they insert all sorts of behind-the-scenes
239 information, although some allow you to save files as "Text
240 Only". You can also download text editors designed
241 specifically for programming, such as Textpad
242 ( http://www.textpad.com/ ) and UltraEdit
243 ( http://www.ultraedit.com/ ), among others.
245 If you are using MacOS, the same concerns apply. MacPerl
246 (for Classic environments) comes with a simple editor.
247 Popular external editors are BBEdit ( http://www.bbedit.com/ )
248 or Alpha ( http://www.kelehers.org/alpha/ ). MacOS X users can
249 use Unix editors as well.
255 http://www.gnu.org/software/emacs/windows/ntemacs.html
259 http://members.nbci.com/uemacs/
263 http://www.xemacs.org/Download/index.html
267 or a vi clone such as
273 ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/
283 win32: http://www.cs.vu.nl/%7Etmgil/vi.html
287 For vi lovers in general, Windows or elsewhere:
289 http://www.thomer.com/thomer/vi/vi.html
291 nvi ( http://www.bostic.com/vi/ , available from CPAN in src/misc/) is
292 yet another vi clone, unfortunately not available for Windows, but in
293 UNIX platforms you might be interested in trying it out, firstly because
294 strictly speaking it is not a vi clone, it is the real vi, or the new
295 incarnation of it, and secondly because you can embed Perl inside it
296 to use Perl as the scripting language. nvi is not alone in this,
297 though: at least also vim and vile offer an embedded Perl.
299 The following are Win32 multilanguage editor/IDESs that support Perl:
305 http://www.starbase.com/
309 http://www.MultiEdit.com/
313 http://www.slickedit.com/
317 There is also a toyedit Text widget based editor written in Perl
318 that is distributed with the Tk module on CPAN. The ptkdb
319 ( http://world.std.com/~aep/ptkdb/ ) is a Perl/tk based debugger that
320 acts as a development environment of sorts. Perl Composer
321 ( http://perlcomposer.sourceforge.net/vperl.html ) is an IDE for Perl/Tk
324 In addition to an editor/IDE you might be interested in a more
325 powerful shell environment for Win32. Your options include
331 from the Cygwin package ( http://sources.redhat.com/cygwin/ )
335 from the MKS Toolkit ( http://www.mks.com/ ), or the Bourne shell of
336 the U/WIN environment ( http://www.research.att.com/sw/tools/uwin/ )
340 ftp://ftp.astron.com/pub/tcsh/ , see also
341 http://www.primate.wisc.edu/software/csh-tcsh-book/
345 ftp://ftp.blarg.net/users/amol/zsh/ , see also http://www.zsh.org/
349 MKS and U/WIN are commercial (U/WIN is free for educational and
350 research purposes), Cygwin is covered by the GNU Public License (but
351 that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all
352 contain (in addition to the shells) a comprehensive set of standard
353 UNIX toolkit utilities.
355 If you're transferring text files between Unix and Windows using FTP
356 be sure to transfer them in ASCII mode so the ends of lines are
357 appropriately converted.
359 On Mac OS the MacPerl Application comes with a simple 32k text editor
360 that behaves like a rudimentary IDE. In contrast to the MacPerl Application
361 the MPW Perl tool can make use of the MPW Shell itself as an editor (with
366 =item BBEdit and BBEdit Lite
368 are text editors for Mac OS that have a Perl sensitivity mode
369 ( http://web.barebones.com/ ).
373 is an editor, written and extensible in Tcl, that nonetheless has
374 built in support for several popular markup and programming languages
375 including Perl and HTML ( http://alpha.olm.net/ ).
379 Pepper and Pe are programming language sensitive text editors for Mac
380 OS X and BeOS respectively ( http://www.hekkelman.com/ ).
382 =head2 Where can I get Perl macros for vi?
384 For a complete version of Tom Christiansen's vi configuration file,
385 see http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz ,
386 the standard benchmark file for vi emulators. The file runs best with nvi,
387 the current version of vi out of Berkeley, which incidentally can be built
388 with an embedded Perl interpreter--see http://www.cpan.org/src/misc/ .
390 =head2 Where can I get perl-mode for emacs?
392 Since Emacs version 19 patchlevel 22 or so, there have been both a
393 perl-mode.el and support for the Perl debugger built in. These should
394 come with the standard Emacs 19 distribution.
396 In the Perl source directory, you'll find a directory called "emacs",
397 which contains a cperl-mode that color-codes keywords, provides
398 context-sensitive help, and other nifty things.
400 Note that the perl-mode of emacs will have fits with C<"main'foo">
401 (single quote), and mess up the indentation and highlighting. You
402 are probably using C<"main::foo"> in new Perl code anyway, so this
403 shouldn't be an issue.
405 =head2 How can I use curses with Perl?
407 The Curses module from CPAN provides a dynamically loadable object
408 module interface to a curses library. A small demo can be found at the
409 directory http://www.cpan.org/authors/Tom_Christiansen/scripts/rep ;
410 this program repeats a command and updates the screen as needed, rendering
411 B<rep ps axu> similar to B<top>.
413 =head2 How can I use X or Tk with Perl?
415 Tk is a completely Perl-based, object-oriented interface to the Tk toolkit
416 that doesn't force you to use Tcl just to get at Tk. Sx is an interface
417 to the Athena Widget set. Both are available from CPAN. See the
418 directory http://www.cpan.org/modules/by-category/08_User_Interfaces/
420 Invaluable for Perl/Tk programming are the Perl/Tk FAQ at
421 http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference
423 http://www.cpan.org/authors/Stephen_O_Lidie/ , and the
425 http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html .
427 =head2 How can I generate simple menus without using CGI or Tk?
429 The http://www.cpan.org/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
430 module, which is curses-based, can help with this.
432 =head2 How can I make my Perl program run faster?
434 The best way to do this is to come up with a better algorithm. This
435 can often make a dramatic difference. Jon Bentley's book
436 ``Programming Pearls'' (that's not a misspelling!) has some good tips
437 on optimization, too. Advice on benchmarking boils down to: benchmark
438 and profile to make sure you're optimizing the right part, look for
439 better algorithms instead of microtuning your code, and when all else
440 fails consider just buying faster hardware. You will probably want to
441 read the answer to the earlier question ``How do I profile my Perl programs?''
442 if you haven't done so already.
444 A different approach is to autoload seldom-used Perl code. See the
445 AutoSplit and AutoLoader modules in the standard distribution for
446 that. Or you could locate the bottleneck and think about writing just
447 that part in C, the way we used to take bottlenecks in C code and
448 write them in assembler. Similar to rewriting in C,
449 modules that have critical sections can be written in C (for instance, the
450 PDL module from CPAN).
452 In some cases, it may be worth it to use the backend compiler to
453 produce byte code (saving compilation time) or compile into C, which
454 will certainly save compilation time and sometimes a small amount (but
455 not much) execution time. See the question about compiling your Perl
456 programs for more on the compiler--the wins aren't as obvious as you'd
459 If you're currently linking your perl executable to a shared I<libc.so>,
460 you can often gain a 10-25% performance benefit by rebuilding it to
461 link with a static libc.a instead. This will make a bigger perl
462 executable, but your Perl programs (and programmers) may thank you for
463 it. See the F<INSTALL> file in the source distribution for more
466 Unsubstantiated reports allege that Perl interpreters that use sfio
467 outperform those that don't (for I/O intensive applications). To try
468 this, see the F<INSTALL> file in the source distribution, especially
469 the ``Selecting File I/O mechanisms'' section.
471 The undump program was an old attempt to speed up your Perl program
472 by storing the already-compiled form to disk. This is no longer
473 a viable option, as it only worked on a few architectures, and
474 wasn't a good solution anyway.
476 =head2 How can I make my Perl program take less memory?
478 When it comes to time-space tradeoffs, Perl nearly always prefers to
479 throw memory at a problem. Scalars in Perl use more memory than
480 strings in C, arrays take more than that, and hashes use even more. While
481 there's still a lot to be done, recent releases have been addressing
482 these issues. For example, as of 5.004, duplicate hash keys are
483 shared amongst all hashes using them, so require no reallocation.
485 In some cases, using substr() or vec() to simulate arrays can be
486 highly beneficial. For example, an array of a thousand booleans will
487 take at least 20,000 bytes of space, but it can be turned into one
488 125-byte bit vector--a considerable memory savings. The standard
489 Tie::SubstrHash module can also help for certain types of data
490 structure. If you're working with specialist data structures
491 (matrices, for instance) modules that implement these in C may use
492 less memory than equivalent Perl modules.
494 Another thing to try is learning whether your Perl was compiled with
495 the system malloc or with Perl's builtin malloc. Whichever one it
496 is, try using the other one and see whether this makes a difference.
497 Information about malloc is in the F<INSTALL> file in the source
498 distribution. You can find out whether you are using perl's malloc by
499 typing C<perl -V:usemymalloc>.
501 Of course, the best way to save memory is to not do anything to waste
502 it in the first place. Good programming practices can go a long way
509 Don't read an entire file into memory if you can process it line
510 by line. Or more concretely, use a loop like this:
529 When the files you're processing are small, it doesn't much matter which
530 way you do it, but it makes a huge difference when they start getting
533 =item * Use map and grep selectively
535 Remember that both map and grep expect a LIST argument, so doing this:
537 @wanted = grep {/pattern/} <FILE>;
539 will cause the entire file to be slurped. For large files, it's better
543 push(@wanted, $_) if /pattern/;
546 =item * Avoid unnecessary quotes and stringification
548 Don't quote large strings unless absolutely necessary:
550 my $copy = "$large_string";
552 makes 2 copies of $large_string (one for $copy and another for the
555 my $copy = $large_string;
559 Ditto for stringifying large arrays:
566 is much more memory-efficient than either
568 print join "\n", @big_array;
578 =item * Pass by reference
580 Pass arrays and hashes by reference, not by value. For one thing, it's
581 the only way to pass multiple lists or hashes (or both) in a single
582 call/return. It also avoids creating a copy of all the contents. This
583 requires some judgment, however, because any changes will be propagated
584 back to the original data. If you really want to mangle (er, modify) a
585 copy, you'll have to sacrifice the memory needed to make one.
587 =item * Tie large variables to disk.
589 For "big" data stores (i.e. ones that exceed available memory) consider
590 using one of the DB modules to store it on disk instead of in RAM. This
591 will incur a penalty in access time, but that's probably better that
592 causing your hard disk to thrash due to massive swapping.
596 =head2 Is it unsafe to return a pointer to local data?
598 No, Perl's garbage collection system takes care of this.
606 push @many, makeone();
609 print $many[4][5], "\n";
613 =head2 How can I free an array or hash so my program shrinks?
615 You can't. On most operating systems, memory allocated to a program
616 can never be returned to the system. That's why long-running programs
617 sometimes re-exec themselves. Some operating systems (notably,
618 FreeBSD and Linux) allegedly reclaim large chunks of memory that is no
619 longer used, but it doesn't appear to happen with Perl (yet). The Mac
620 appears to be the only platform that will reliably (albeit, slowly)
621 return memory to the OS.
623 We've had reports that on Linux (Redhat 5.1) on Intel, C<undef
624 $scalar> will return memory to the system, while on Solaris 2.6 it
625 won't. In general, try it yourself and see.
627 However, judicious use of my() on your variables will help make sure
628 that they go out of scope so that Perl can free up that space for
629 use in other parts of your program. A global variable, of course, never
630 goes out of scope, so you can't get its space automatically reclaimed,
631 although undef()ing and/or delete()ing it will achieve the same effect.
632 In general, memory allocation and de-allocation isn't something you can
633 or should be worrying about much in Perl, but even this capability
634 (preallocation of data types) is in the works.
636 =head2 How can I make my CGI script more efficient?
638 Beyond the normal measures described to make general Perl programs
639 faster or smaller, a CGI program has additional issues. It may be run
640 several times per second. Given that each time it runs it will need
641 to be re-compiled and will often allocate a megabyte or more of system
642 memory, this can be a killer. Compiling into C B<isn't going to help
643 you> because the process start-up overhead is where the bottleneck is.
645 There are two popular ways to avoid this overhead. One solution
646 involves running the Apache HTTP server (available from
647 http://www.apache.org/ ) with either of the mod_perl or mod_fastcgi
650 With mod_perl and the Apache::Registry module (distributed with
651 mod_perl), httpd will run with an embedded Perl interpreter which
652 pre-compiles your script and then executes it within the same address
653 space without forking. The Apache extension also gives Perl access to
654 the internal server API, so modules written in Perl can do just about
655 anything a module written in C can. For more on mod_perl, see
656 http://perl.apache.org/
658 With the FCGI module (from CPAN) and the mod_fastcgi
659 module (available from http://www.fastcgi.com/ ) each of your Perl
660 programs becomes a permanent CGI daemon process.
662 Both of these solutions can have far-reaching effects on your system
663 and on the way you write your CGI programs, so investigate them with
666 See http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
668 A non-free, commercial product, ``The Velocity Engine for Perl'',
669 (http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ )
670 might also be worth looking at. It will allow you to increase the
671 performance of your Perl programs, running programs up to 25 times
672 faster than normal CGI Perl when running in persistent Perl mode or 4
673 to 5 times faster without any modification to your existing CGI
674 programs. Fully functional evaluation copies are available from the
677 =head2 How can I hide the source for my Perl program?
679 Delete it. :-) Seriously, there are a number of (mostly
680 unsatisfactory) solutions with varying levels of ``security''.
682 First of all, however, you I<can't> take away read permission, because
683 the source code has to be readable in order to be compiled and
684 interpreted. (That doesn't mean that a CGI script's source is
685 readable by people on the web, though--only by people with access to
686 the filesystem.) So you have to leave the permissions at the socially
689 Some people regard this as a security problem. If your program does
690 insecure things and relies on people not knowing how to exploit those
691 insecurities, it is not secure. It is often possible for someone to
692 determine the insecure things and exploit them without viewing the
693 source. Security through obscurity, the name for hiding your bugs
694 instead of fixing them, is little security indeed.
696 You can try using encryption via source filters (Starting from Perl
697 5.8 the Filter::Simple and Filter::Util::Call modules are included in
698 the standard distribution), but any decent programmer will be able to
699 decrypt it. You can try using the byte code compiler and interpreter
700 described below, but the curious might still be able to de-compile it.
701 You can try using the native-code compiler described below, but
702 crackers might be able to disassemble it. These pose varying degrees
703 of difficulty to people wanting to get at your code, but none can
704 definitively conceal it (true of every language, not just Perl).
706 If you're concerned about people profiting from your code, then the
707 bottom line is that nothing but a restrictive license will give you
708 legal security. License your software and pepper it with threatening
709 statements like ``This is unpublished proprietary software of XYZ Corp.
710 Your access to it does not give you permission to use it blah blah
711 blah.'' We are not lawyers, of course, so you should see a lawyer if
712 you want to be sure your license's wording will stand up in court.
714 =head2 How can I compile my Perl program into byte code or C?
716 Malcolm Beattie has written a multifunction backend compiler,
717 available from CPAN, that can do both these things. It is included
718 in the perl5.005 release, but is still considered experimental.
719 This means it's fun to play with if you're a programmer but not
720 really for people looking for turn-key solutions.
722 Merely compiling into C does not in and of itself guarantee that your
723 code will run very much faster. That's because except for lucky cases
724 where a lot of native type inferencing is possible, the normal Perl
725 run-time system is still present and so your program will take just as
726 long to run and be just as big. Most programs save little more than
727 compilation time, leaving execution no more than 10-30% faster. A few
728 rare programs actually benefit significantly (even running several times
729 faster), but this takes some tweaking of your code.
731 You'll probably be astonished to learn that the current version of the
732 compiler generates a compiled form of your script whose executable is
733 just as big as the original perl executable, and then some. That's
734 because as currently written, all programs are prepared for a full
735 eval() statement. You can tremendously reduce this cost by building a
736 shared I<libperl.so> library and linking against that. See the
737 F<INSTALL> podfile in the Perl source distribution for details. If
738 you link your main perl binary with this, it will make it minuscule.
739 For example, on one author's system, F</usr/bin/perl> is only 11k in
742 In general, the compiler will do nothing to make a Perl program smaller,
743 faster, more portable, or more secure. In fact, it can make your
744 situation worse. The executable will be bigger, your VM system may take
745 longer to load the whole thing, the binary is fragile and hard to fix,
746 and compilation never stopped software piracy in the form of crackers,
747 viruses, or bootleggers. The real advantage of the compiler is merely
748 packaging, and once you see the size of what it makes (well, unless
749 you use a shared I<libperl.so>), you'll probably want a complete
752 =head2 How can I compile Perl into Java?
754 You can also integrate Java and Perl with the
755 Perl Resource Kit from O'Reilly and Associates. See
756 http://www.oreilly.com/catalog/prkunix/ .
758 Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in
759 development, allows Perl code to be called from Java. See jpl/README
760 in the Perl source tree.
762 =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
766 extproc perl -S -your_switches
768 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
769 `extproc' handling). For DOS one should first invent a corresponding
770 batch file and codify it in C<ALTERNATIVE_SHEBANG> (see the
771 F<INSTALL> file in the source distribution for more information).
773 The Win95/NT installation, when using the ActiveState port of Perl,
774 will modify the Registry to associate the C<.pl> extension with the
775 perl interpreter. If you install another port, perhaps even building
776 your own Win95/NT Perl from the standard sources by using a Windows port
777 of gcc (e.g., with cygwin or mingw32), then you'll have to modify
778 the Registry yourself. In addition to associating C<.pl> with the
779 interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them
780 run the program C<install-linux.pl> merely by typing C<install-linux>.
782 Macintosh Perl programs will have the appropriate Creator and
783 Type, so that double-clicking them will invoke the Perl application.
785 I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
786 throw the perl interpreter into your cgi-bin directory, in order to
787 get your programs working for a web server. This is an EXTREMELY big
788 security risk. Take the time to figure out how to do it correctly.
790 =head2 Can I write useful Perl programs on the command line?
792 Yes. Read L<perlrun> for more information. Some examples follow.
793 (These assume standard Unix shell quoting rules.)
795 # sum first and last fields
796 perl -lane 'print $F[0] + $F[-1]' *
798 # identify text files
799 perl -le 'for(@ARGV) {print if -f && -T _}' *
801 # remove (most) comments from C program
802 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
804 # make file a month younger than today, defeating reaper daemons
805 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
807 # find first unused uid
808 perl -le '$i++ while getpwuid($i); print $i'
810 # display reasonable manpath
811 echo $PATH | perl -nl -072 -e '
812 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
814 OK, the last one was actually an Obfuscated Perl Contest entry. :-)
816 =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system?
818 The problem is usually that the command interpreters on those systems
819 have rather different ideas about quoting than the Unix shells under
820 which the one-liners were created. On some systems, you may have to
821 change single-quotes to double ones, which you must I<NOT> do on Unix
822 or Plan9 systems. You might also have to change a single % to a %%.
827 perl -e 'print "Hello world\n"'
830 perl -e "print \"Hello world\n\""
833 print "Hello world\n"
834 (then Run "Myscript" or Shift-Command-R)
837 perl -e 'print "Hello world\n"'
840 perl -e "print ""Hello world\n"""
842 The problem is that none of these examples are reliable: they depend on the
843 command interpreter. Under Unix, the first two often work. Under DOS,
844 it's entirely possible that neither works. If 4DOS was the command shell,
845 you'd probably have better luck like this:
847 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
849 Under the Mac, it depends which environment you are using. The MacPerl
850 shell, or MPW, is much like Unix shells in its support for several
851 quoting variants, except that it makes free use of the Mac's non-ASCII
852 characters as control characters.
854 Using qq(), q(), and qx(), instead of "double quotes", 'single
855 quotes', and `backticks`, may make one-liners easier to write.
857 There is no general solution to all of this. It is a mess.
859 [Some of this answer was contributed by Kenneth Albanowski.]
861 =head2 Where can I learn about CGI or Web programming in Perl?
863 For modules, get the CGI or LWP modules from CPAN. For textbooks,
864 see the two especially dedicated to web stuff in the question on
865 books. For problems and questions related to the web, like ``Why
866 do I get 500 Errors'' or ``Why doesn't it run from the browser right
867 when it runs fine on the command line'', see the troubleshooting
868 guides and references in L<perlfaq9> or in the CGI MetaFAQ:
870 http://www.perl.org/CGI_MetaFAQ.html
872 =head2 Where can I learn about object-oriented Perl programming?
874 A good place to start is L<perltoot>, and you can use L<perlobj>,
875 L<perlboot>, L<perltoot>, L<perltooc>, and L<perlbot> for reference.
876 (If you are using really old Perl, you may not have all of these,
877 try http://www.perldoc.com/ , but consider upgrading your perl.)
879 A good book on OO on Perl is the "Object-Oriented Perl"
880 by Damian Conway from Manning Publications,
881 http://www.manning.com/Conway/index.html
883 =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp]
885 If you want to call C from Perl, start with L<perlxstut>,
886 moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to
887 call Perl from C, then read L<perlembed>, L<perlcall>, and
888 L<perlguts>. Don't forget that you can learn a lot from looking at
889 how the authors of existing extension modules wrote their code and
890 solved their problems.
892 =head2 I've read perlembed, perlguts, etc., but I can't embed perl in
893 my C program; what am I doing wrong?
895 Download the ExtUtils::Embed kit from CPAN and run `make test'. If
896 the tests pass, read the pods again and again and again. If they
897 fail, see L<perlbug> and send a bug report with the output of
898 C<make test TEST_VERBOSE=1> along with C<perl -V>.
900 =head2 When I tried to run my script, I got this message. What does it mean?
902 A complete list of Perl's error messages and warnings with explanatory
903 text can be found in L<perldiag>. You can also use the splain program
904 (distributed with Perl) to explain the error messages:
906 perl program 2>diag.out
907 splain [-v] [-p] diag.out
909 or change your program to explain the messages for you:
915 use diagnostics -verbose;
917 =head2 What's MakeMaker?
919 This module (part of the standard Perl distribution) is designed to
920 write a Makefile for an extension module from a Makefile.PL. For more
921 information, see L<ExtUtils::MakeMaker>.
923 =head1 AUTHOR AND COPYRIGHT
925 Copyright (c) 1997-2002 Tom Christiansen and Nathan Torkington.
928 This documentation is free; you can redistribute it and/or modify it
929 under the same terms as Perl itself.
931 Irrespective of its distribution, all code examples here are in the public
932 domain. You are permitted and encouraged to use this code and any
933 derivatives thereof in your own programs for fun or for profit as you
934 see fit. A simple comment in the code giving credit to the FAQ would
935 be courteous but is not required.