3 perlfaq3 - Programming Tools ($Revision: 1.6 $, $Date: 2001/10/03 23:06:15 $)
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.perl.com/CPAN/doc/FMTEYEWTK/index.html
26 (not a man-page but still useful)
28 A crude table of contents for the Perl manpage set is found in L<perltoc>.
30 =head2 How can I use Perl interactively?
32 The typical approach uses the Perl debugger, described in the
33 perldebug(1) manpage, on an ``empty'' program, like this:
37 Now just type in any legal Perl code, and it will be immediately
38 evaluated. You can also examine the symbol table, get stack
39 backtraces, check variable values, set breakpoints, and other
40 operations typically found in symbolic debuggers.
42 =head2 Is there a Perl shell?
44 In general, not yet. There is psh available at
46 http://www.focusresearch.com/gregor/psh
48 Which includes the following description:
50 The Perl Shell is a shell that combines the interactive nature
51 of a Unix shell with the power of Perl. The goal is to eventually
52 have a full featured shell that behaves as expected for normal
53 shell activity. But, the Perl Shell will use Perl syntax and
54 functionality for for control-flow statements and other things.
56 The Shell.pm module (distributed with Perl) makes Perl try commands
57 which aren't part of the Perl language as shell commands. perlsh
58 from the source distribution is simplistic and uninteresting, but
59 may still be what you want.
61 =head2 How do I debug my Perl programs?
63 Have you tried C<use warnings> or used C<-w>? They enable warnings
64 to detect dubious practices.
66 Have you tried C<use strict>? It prevents you from using symbolic
67 references, makes you predeclare any subroutines that you call as bare
68 words, and (probably most importantly) forces you to predeclare your
69 variables with C<my>, C<our>, or C<use vars>.
71 Did you check the return values of each and every system call? The operating
72 system (and thus Perl) tells you whether they worked, and if not
75 open(FH, "> /etc/cantwrite")
76 or die "Couldn't write to /etc/cantwrite: $!\n";
78 Did you read L<perltrap>? It's full of gotchas for old and new Perl
79 programmers and even has sections for those of you who are upgrading
80 from languages like I<awk> and I<C>.
82 Have you tried the Perl debugger, described in L<perldebug>? You can
83 step through your program and see what it's doing and thus work out
84 why what it's doing isn't what it should be doing.
86 =head2 How do I profile my Perl programs?
88 You should get the Devel::DProf module from the standard distribution
89 (or separately on CPAN) and also use Benchmark.pm from the standard
90 distribution. The Benchmark module lets you time specific portions of
91 your code, while Devel::DProf gives detailed breakdowns of where your
94 Here's a sample use of Benchmark:
98 @junk = `cat /etc/motd`;
102 'map' => sub { my @a = @junk;
106 'for' => sub { my @a = @junk;
112 This is what it prints (on one machine--your results will be dependent
113 on your hardware, operating system, and the load on your machine):
115 Benchmark: timing 10000 iterations of for, map...
116 for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu)
117 map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu)
119 Be aware that a good benchmark is very hard to write. It only tests the
120 data you give it and proves little about the differing complexities
121 of contrasting algorithms.
123 =head2 How do I cross-reference my Perl programs?
125 The B::Xref module, shipped with the new, alpha-release Perl compiler
126 (not the general distribution prior to the 5.005 release), can be used
127 to generate cross-reference reports for Perl programs.
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.perl.com/CPAN-local/authors/id/TOMC/scripts/toms.exrc.gz
157 If you are used to using the I<vgrind> program for printing out nice code
158 to a laser printer, you can take a stab at this using
159 http://www.perl.com/CPAN/doc/misc/tips/working.vgrind.entry, but the
160 results are not particularly satisfying for sophisticated code.
162 The a2ps at http://www.infres.enst.fr/%7Edemaille/a2ps/ does lots of things
163 related to generating nicely printed output of documents.
165 =head2 Is there a ctags for Perl?
167 Recent versions of ctags do much more than older versions did.
168 EXUBERANT CTAGS is available from http://ctags.sourceforge.net/
169 and does a good job of making tags files for perl code.
171 There is also a simple one at
172 http://www.perl.com/CPAN/authors/id/TOMC/scripts/ptags.gz which may do
173 the trick. It can be easy to hack this into what you want.
175 =head2 Is there an IDE or Windows Perl Editor?
177 Perl programs are just plain text, so any editor will do.
179 If you're on Unix, you already have an IDE--Unix itself. The UNIX
180 philosophy is the philosophy of several small tools that each do one
181 thing and do it well. It's like a carpenter's toolbox.
183 If you want an IDE, check the following:
189 ActiveState's cross-platform (as of April 2001 Windows and Linux),
190 multi-language IDE has Perl support, including a regular expression
191 debugger and remote debugging
192 (http://www.ActiveState.com/Products/Komodo/index.html). (Visual
193 Perl, a Visual Studio.NET plug-in is currently (early 2001) in beta
194 (http://www.ActiveState.com/Products/VisualPerl/index.html)).
196 =item The Object System
198 (http://www.castlelink.co.uk/object_system/) is a Perl web
199 applications development IDE, apparently for any platform
204 ( http://open-perl-ide.sourceforge.net/ )
205 Open Perl IDE is an integrated development environment for writing
206 and debugging Perl scripts with ActiveState's ActivePerl distribution
207 under Windows 95/98/NT/2000.
211 (http://www.solutionsoft.com/perl.htm) is an integrated development
212 environment for Windows that supports Perl development.
216 ( http://helpconsulting.net/visiperl/ )
217 From Help Consulting, for Windows.
221 For Windows there's also the
227 ( http://www.codemagiccd.com/ ) Collection of various programming
228 tools for Windows: Perl (5.005_03), TclTk, Python, GNU programming
229 tools, REBOL, wxWindows toolkit, the MinGW GNU C/C++ compiler, DJGPP
230 GNU C/C++ compiler, Cint C interpreter, YaBasic.
234 For editors: if you're on Unix you probably have vi or a vi clone already,
235 and possibly an emacs too, so you may not need to download anything.
236 In any emacs the cperl-mode (M-x cperl-mode) gives you perhaps the
237 best available Perl editing mode in any editor.
239 For Windows editors: you can download an Emacs
245 http://www.gnu.org/software/emacs/windows/ntemacs.html
249 http://members.nbci.com/uemacs/
253 http://www.xemacs.org/Download/index.html
257 or a vi clone such as
263 ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/
273 win32: http://www.cs.vu.nl/%7Etmgil/vi.html
277 For vi lovers in general, Windows or elsewhere:
278 http://www.thomer.com/thomer/vi/vi.html.
280 nvi (http://www.bostic.com/vi/, available from CPAN in src/misc/) is
281 yet another vi clone, unfortunately not available for Windows, but in
282 UNIX platforms you might be interested in trying it out, firstly because
283 strictly speaking it is not a vi clone, it is the real vi, or the new
284 incarnation of it, and secondly because you can embed Perl inside it
285 to use Perl as the scripting language. nvi is not alone in this,
286 though: at least also vim and vile offer an embedded Perl.
288 The following are Win32 multilanguage editor/IDESs that support Perl:
294 http://www.starbase.com/
298 http://www.MultiEdit.com/
302 http://www.slickedit.com/
306 There is also a toyedit Text widget based editor written in Perl
307 that is distributed with the Tk module on CPAN. The ptkdb
308 (http://world.std.com/~aep/ptkdb/) is a Perl/tk based debugger that
309 acts as a development environment of sorts. Perl Composer
310 (http://perlcomposer.sourceforge.net/vperl.html) is an IDE for Perl/Tk
313 In addition to an editor/IDE you might be interested in a more
314 powerful shell environment for Win32. Your options include
320 from the Cygwin package (http://sources.redhat.com/cygwin/)
324 from the MKS Toolkit (http://www.mks.com/), or the Bourne shell of
325 the U/WIN environment (http://www.research.att.com/sw/tools/uwin/)
329 ftp://ftp.astron.com/pub/tcsh/, see also
330 http://www.primate.wisc.edu/software/csh-tcsh-book/
334 ftp://ftp.blarg.net/users/amol/zsh/, see also http://www.zsh.org/
338 MKS and U/WIN are commercial (U/WIN is free for educational and
339 research purposes), Cygwin is covered by the GNU Public License (but
340 that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all
341 contain (in addition to the shells) a comprehensive set of standard
342 UNIX toolkit utilities.
344 If you're transferring text files between Unix and Windows using FTP
345 be sure to transfer them in ASCII mode so the ends of lines are
346 appropriately converted.
348 On Mac OS the MacPerl Application comes with a simple 32k text editor
349 that behaves like a rudimentary IDE. In contrast to the MacPerl Application
350 the MPW Perl tool can make use of the MPW Shell itself as an editor (with
355 =item BBEdit and BBEdit Lite
357 are text editors for Mac OS that have a Perl sensitivity mode
358 (http://web.barebones.com/).
362 is an editor, written and extensible in Tcl, that nonetheless has
363 built in support for several popular markup and programming languages
364 including Perl and HTML (http://alpha.olm.net/).
368 Pepper and Pe are programming language sensitive text editors for Mac
369 OS X and BeOS respectively (http://www.hekkelman.com/).
371 =head2 Where can I get Perl macros for vi?
373 For a complete version of Tom Christiansen's vi configuration file,
374 see http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc.gz ,
375 the standard benchmark file for vi emulators. The file runs best with nvi,
376 the current version of vi out of Berkeley, which incidentally can be built
377 with an embedded Perl interpreter--see http://www.perl.com/CPAN/src/misc.
379 =head2 Where can I get perl-mode for emacs?
381 Since Emacs version 19 patchlevel 22 or so, there have been both a
382 perl-mode.el and support for the Perl debugger built in. These should
383 come with the standard Emacs 19 distribution.
385 In the Perl source directory, you'll find a directory called "emacs",
386 which contains a cperl-mode that color-codes keywords, provides
387 context-sensitive help, and other nifty things.
389 Note that the perl-mode of emacs will have fits with C<"main'foo">
390 (single quote), and mess up the indentation and highlighting. You
391 are probably using C<"main::foo"> in new Perl code anyway, so this
392 shouldn't be an issue.
394 =head2 How can I use curses with Perl?
396 The Curses module from CPAN provides a dynamically loadable object
397 module interface to a curses library. A small demo can be found at the
398 directory http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep;
399 this program repeats a command and updates the screen as needed, rendering
400 B<rep ps axu> similar to B<top>.
402 =head2 How can I use X or Tk with Perl?
404 Tk is a completely Perl-based, object-oriented interface to the Tk toolkit
405 that doesn't force you to use Tcl just to get at Tk. Sx is an interface
406 to the Athena Widget set. Both are available from CPAN. See the
407 directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/
409 Invaluable for Perl/Tk programming are the Perl/Tk FAQ at
410 http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference
412 http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ , and the
414 http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html .
416 =head2 How can I generate simple menus without using CGI or Tk?
418 The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
419 module, which is curses-based, can help with this.
421 =head2 What is undump?
423 See the next question on ``How can I make my Perl program run faster?''
425 =head2 How can I make my Perl program run faster?
427 The best way to do this is to come up with a better algorithm. This
428 can often make a dramatic difference. Jon Bentley's book
429 ``Programming Pearls'' (that's not a misspelling!) has some good tips
430 on optimization, too. Advice on benchmarking boils down to: benchmark
431 and profile to make sure you're optimizing the right part, look for
432 better algorithms instead of microtuning your code, and when all else
433 fails consider just buying faster hardware. You will probably want to
434 read the answer to the earlier question ``How do I profile my Perl programs?''
435 if you haven't done so already.
437 A different approach is to autoload seldom-used Perl code. See the
438 AutoSplit and AutoLoader modules in the standard distribution for
439 that. Or you could locate the bottleneck and think about writing just
440 that part in C, the way we used to take bottlenecks in C code and
441 write them in assembler. Similar to rewriting in C,
442 modules that have critical sections can be written in C (for instance, the
443 PDL module from CPAN).
445 In some cases, it may be worth it to use the backend compiler to
446 produce byte code (saving compilation time) or compile into C, which
447 will certainly save compilation time and sometimes a small amount (but
448 not much) execution time. See the question about compiling your Perl
449 programs for more on the compiler--the wins aren't as obvious as you'd
452 If you're currently linking your perl executable to a shared I<libc.so>,
453 you can often gain a 10-25% performance benefit by rebuilding it to
454 link with a static libc.a instead. This will make a bigger perl
455 executable, but your Perl programs (and programmers) may thank you for
456 it. See the F<INSTALL> file in the source distribution for more
459 Unsubstantiated reports allege that Perl interpreters that use sfio
460 outperform those that don't (for I/O intensive applications). To try
461 this, see the F<INSTALL> file in the source distribution, especially
462 the ``Selecting File I/O mechanisms'' section.
464 The undump program was an old attempt to speed up your Perl program
465 by storing the already-compiled form to disk. This is no longer
466 a viable option, as it only worked on a few architectures, and
467 wasn't a good solution anyway.
469 =head2 How can I make my Perl program take less memory?
471 When it comes to time-space tradeoffs, Perl nearly always prefers to
472 throw memory at a problem. Scalars in Perl use more memory than
473 strings in C, arrays take more than that, and hashes use even more. While
474 there's still a lot to be done, recent releases have been addressing
475 these issues. For example, as of 5.004, duplicate hash keys are
476 shared amongst all hashes using them, so require no reallocation.
478 In some cases, using substr() or vec() to simulate arrays can be
479 highly beneficial. For example, an array of a thousand booleans will
480 take at least 20,000 bytes of space, but it can be turned into one
481 125-byte bit vector--a considerable memory savings. The standard
482 Tie::SubstrHash module can also help for certain types of data
483 structure. If you're working with specialist data structures
484 (matrices, for instance) modules that implement these in C may use
485 less memory than equivalent Perl modules.
487 Another thing to try is learning whether your Perl was compiled with
488 the system malloc or with Perl's builtin malloc. Whichever one it
489 is, try using the other one and see whether this makes a difference.
490 Information about malloc is in the F<INSTALL> file in the source
491 distribution. You can find out whether you are using perl's malloc by
492 typing C<perl -V:usemymalloc>.
494 Of course, the best way to save memory is to not do anything to waste
495 it in the first place. Good programming practices can go a long way
502 Don't read an entire file into memory if you can process it line
503 by line. Or more concretely, use a loop like this:
522 When the files you're processing are small, it doesn't much matter which
523 way you do it, but it makes a huge difference when they start getting
526 =item * Use map and grep selectively
528 Remember that both map and grep expect a LIST argument, so doing this:
530 @wanted = grep {/pattern/} <FILE>;
532 will cause the entire file to be slurped. For large files, it's better
536 push(@wanted, $_) if /pattern/;
539 =item * Avoid unnecessary quotes and stringification
541 Don't quote large strings unless absolutely necessary:
543 my $copy = "$large_string";
545 makes 2 copies of $large_string (one for $copy and another for the
548 my $copy = $large_string;
552 Ditto for stringifying large arrays:
559 is much more memory-efficient than either
561 print join "\n", @big_array;
571 =item * Pass by reference
573 Pass arrays and hashes by reference, not by value. For one thing, it's
574 the only way to pass multiple lists or hashes (or both) in a single
575 call/return. It also avoids creating a copy of all the contents. This
576 requires some judgment, however, because any changes will be propagated
577 back to the original data. If you really want to mangle (er, modify) a
578 copy, you'll have to sacrifice the memory needed to make one.
580 =item * Tie large variables to disk.
582 For "big" data stores (i.e. ones that exceed available memory) consider
583 using one of the DB modules to store it on disk instead of in RAM. This
584 will incur a penalty in access time, but that's probably better that
585 causing your hard disk to thrash due to massive swapping.
589 =head2 Is it unsafe to return a pointer to local data?
591 No, Perl's garbage collection system takes care of this.
599 push @many, makeone();
602 print $many[4][5], "\n";
606 =head2 How can I free an array or hash so my program shrinks?
608 You can't. On most operating systems, memory allocated to a program
609 can never be returned to the system. That's why long-running programs
610 sometimes re-exec themselves. Some operating systems (notably,
611 FreeBSD and Linux) allegedly reclaim large chunks of memory that is no
612 longer used, but it doesn't appear to happen with Perl (yet). The Mac
613 appears to be the only platform that will reliably (albeit, slowly)
614 return memory to the OS.
616 We've had reports that on Linux (Redhat 5.1) on Intel, C<undef
617 $scalar> will return memory to the system, while on Solaris 2.6 it
618 won't. In general, try it yourself and see.
620 However, judicious use of my() on your variables will help make sure
621 that they go out of scope so that Perl can free up that space for
622 use in other parts of your program. A global variable, of course, never
623 goes out of scope, so you can't get its space automatically reclaimed,
624 although undef()ing and/or delete()ing it will achieve the same effect.
625 In general, memory allocation and de-allocation isn't something you can
626 or should be worrying about much in Perl, but even this capability
627 (preallocation of data types) is in the works.
629 =head2 How can I make my CGI script more efficient?
631 Beyond the normal measures described to make general Perl programs
632 faster or smaller, a CGI program has additional issues. It may be run
633 several times per second. Given that each time it runs it will need
634 to be re-compiled and will often allocate a megabyte or more of system
635 memory, this can be a killer. Compiling into C B<isn't going to help
636 you> because the process start-up overhead is where the bottleneck is.
638 There are two popular ways to avoid this overhead. One solution
639 involves running the Apache HTTP server (available from
640 http://www.apache.org/) with either of the mod_perl or mod_fastcgi
643 With mod_perl and the Apache::Registry module (distributed with
644 mod_perl), httpd will run with an embedded Perl interpreter which
645 pre-compiles your script and then executes it within the same address
646 space without forking. The Apache extension also gives Perl access to
647 the internal server API, so modules written in Perl can do just about
648 anything a module written in C can. For more on mod_perl, see
649 http://perl.apache.org/
651 With the FCGI module (from CPAN) and the mod_fastcgi
652 module (available from http://www.fastcgi.com/) each of your Perl
653 programs becomes a permanent CGI daemon process.
655 Both of these solutions can have far-reaching effects on your system
656 and on the way you write your CGI programs, so investigate them with
659 See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
661 A non-free, commercial product, ``The Velocity Engine for Perl'',
662 (http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ )
663 might also be worth looking at. It will allow you to increase the
664 performance of your Perl programs, running programs up to 25 times
665 faster than normal CGI Perl when running in persistent Perl mode or 4
666 to 5 times faster without any modification to your existing CGI
667 programs. Fully functional evaluation copies are available from the
670 =head2 How can I hide the source for my Perl program?
672 Delete it. :-) Seriously, there are a number of (mostly
673 unsatisfactory) solutions with varying levels of ``security''.
675 First of all, however, you I<can't> take away read permission, because
676 the source code has to be readable in order to be compiled and
677 interpreted. (That doesn't mean that a CGI script's source is
678 readable by people on the web, though--only by people with access to
679 the filesystem.) So you have to leave the permissions at the socially
682 Some people regard this as a security problem. If your program does
683 insecure things and relies on people not knowing how to exploit those
684 insecurities, it is not secure. It is often possible for someone to
685 determine the insecure things and exploit them without viewing the
686 source. Security through obscurity, the name for hiding your bugs
687 instead of fixing them, is little security indeed.
689 You can try using encryption via source filters (Starting from Perl
690 5.8 the Filter::Simple and Filter::Util::Call modules are included in
691 the standard distribution), but any decent programmer will be able to
692 decrypt it. You can try using the byte code compiler and interpreter
693 described below, but the curious might still be able to de-compile it.
694 You can try using the native-code compiler described below, but
695 crackers might be able to disassemble it. These pose varying degrees
696 of difficulty to people wanting to get at your code, but none can
697 definitively conceal it (true of every language, not just Perl).
699 If you're concerned about people profiting from your code, then the
700 bottom line is that nothing but a restrictive license will give you
701 legal security. License your software and pepper it with threatening
702 statements like ``This is unpublished proprietary software of XYZ Corp.
703 Your access to it does not give you permission to use it blah blah
704 blah.'' We are not lawyers, of course, so you should see a lawyer if
705 you want to be sure your license's wording will stand up in court.
707 =head2 How can I compile my Perl program into byte code or C?
709 Malcolm Beattie has written a multifunction backend compiler,
710 available from CPAN, that can do both these things. It is included
711 in the perl5.005 release, but is still considered experimental.
712 This means it's fun to play with if you're a programmer but not
713 really for people looking for turn-key solutions.
715 Merely compiling into C does not in and of itself guarantee that your
716 code will run very much faster. That's because except for lucky cases
717 where a lot of native type inferencing is possible, the normal Perl
718 run-time system is still present and so your program will take just as
719 long to run and be just as big. Most programs save little more than
720 compilation time, leaving execution no more than 10-30% faster. A few
721 rare programs actually benefit significantly (even running several times
722 faster), but this takes some tweaking of your code.
724 You'll probably be astonished to learn that the current version of the
725 compiler generates a compiled form of your script whose executable is
726 just as big as the original perl executable, and then some. That's
727 because as currently written, all programs are prepared for a full
728 eval() statement. You can tremendously reduce this cost by building a
729 shared I<libperl.so> library and linking against that. See the
730 F<INSTALL> podfile in the Perl source distribution for details. If
731 you link your main perl binary with this, it will make it minuscule.
732 For example, on one author's system, F</usr/bin/perl> is only 11k in
735 In general, the compiler will do nothing to make a Perl program smaller,
736 faster, more portable, or more secure. In fact, it can make your
737 situation worse. The executable will be bigger, your VM system may take
738 longer to load the whole thing, the binary is fragile and hard to fix,
739 and compilation never stopped software piracy in the form of crackers,
740 viruses, or bootleggers. The real advantage of the compiler is merely
741 packaging, and once you see the size of what it makes (well, unless
742 you use a shared I<libperl.so>), you'll probably want a complete
745 =head2 How can I compile Perl into Java?
747 You can also integrate Java and Perl with the
748 Perl Resource Kit from O'Reilly and Associates. See
749 http://www.oreilly.com/catalog/prkunix/ .
751 Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in
752 development, allows Perl code to be called from Java. See jpl/README
753 in the Perl source tree.
755 =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
759 extproc perl -S -your_switches
761 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
762 `extproc' handling). For DOS one should first invent a corresponding
763 batch file and codify it in C<ALTERNATIVE_SHEBANG> (see the
764 F<INSTALL> file in the source distribution for more information).
766 The Win95/NT installation, when using the ActiveState port of Perl,
767 will modify the Registry to associate the C<.pl> extension with the
768 perl interpreter. If you install another port, perhaps even building
769 your own Win95/NT Perl from the standard sources by using a Windows port
770 of gcc (e.g., with cygwin or mingw32), then you'll have to modify
771 the Registry yourself. In addition to associating C<.pl> with the
772 interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them
773 run the program C<install-linux.pl> merely by typing C<install-linux>.
775 Macintosh Perl programs will have the appropriate Creator and
776 Type, so that double-clicking them will invoke the Perl application.
778 I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
779 throw the perl interpreter into your cgi-bin directory, in order to
780 get your programs working for a web server. This is an EXTREMELY big
781 security risk. Take the time to figure out how to do it correctly.
783 =head2 Can I write useful Perl programs on the command line?
785 Yes. Read L<perlrun> for more information. Some examples follow.
786 (These assume standard Unix shell quoting rules.)
788 # sum first and last fields
789 perl -lane 'print $F[0] + $F[-1]' *
791 # identify text files
792 perl -le 'for(@ARGV) {print if -f && -T _}' *
794 # remove (most) comments from C program
795 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
797 # make file a month younger than today, defeating reaper daemons
798 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
800 # find first unused uid
801 perl -le '$i++ while getpwuid($i); print $i'
803 # display reasonable manpath
804 echo $PATH | perl -nl -072 -e '
805 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
807 OK, the last one was actually an Obfuscated Perl Contest entry. :-)
809 =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system?
811 The problem is usually that the command interpreters on those systems
812 have rather different ideas about quoting than the Unix shells under
813 which the one-liners were created. On some systems, you may have to
814 change single-quotes to double ones, which you must I<NOT> do on Unix
815 or Plan9 systems. You might also have to change a single % to a %%.
820 perl -e 'print "Hello world\n"'
823 perl -e "print \"Hello world\n\""
826 print "Hello world\n"
827 (then Run "Myscript" or Shift-Command-R)
830 perl -e "print ""Hello world\n"""
832 The problem is that none of these examples are reliable: they depend on the
833 command interpreter. Under Unix, the first two often work. Under DOS,
834 it's entirely possible that neither works. If 4DOS was the command shell,
835 you'd probably have better luck like this:
837 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
839 Under the Mac, it depends which environment you are using. The MacPerl
840 shell, or MPW, is much like Unix shells in its support for several
841 quoting variants, except that it makes free use of the Mac's non-ASCII
842 characters as control characters.
844 Using qq(), q(), and qx(), instead of "double quotes", 'single
845 quotes', and `backticks`, may make one-liners easier to write.
847 There is no general solution to all of this. It is a mess, pure and
848 simple. Sucks to be away from Unix, huh? :-)
850 [Some of this answer was contributed by Kenneth Albanowski.]
852 =head2 Where can I learn about CGI or Web programming in Perl?
854 For modules, get the CGI or LWP modules from CPAN. For textbooks,
855 see the two especially dedicated to web stuff in the question on
856 books. For problems and questions related to the web, like ``Why
857 do I get 500 Errors'' or ``Why doesn't it run from the browser right
858 when it runs fine on the command line'', see these sources:
861 http://www.w3.org/Security/Faq/
864 http://www.boutell.com/faq/
867 http://www.webthing.com/tutorials/cgifaq.html
870 http://www.w3.org/pub/WWW/Protocols/HTTP/
873 http://www.w3.org/TR/REC-html40/
874 http://www.w3.org/pub/WWW/MarkUp/
877 http://www.w3.org/CGI/
880 http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt
882 =head2 Where can I learn about object-oriented Perl programming?
884 A good place to start is L<perltoot>, and you can use L<perlobj>,
885 L<perlboot>, and L<perlbot> for reference. Perltoot didn't come out
886 until the 5.004 release; you can get a copy (in pod, html, or
887 postscript) from http://www.perl.com/CPAN/doc/FMTEYEWTK/ .
889 =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp]
891 If you want to call C from Perl, start with L<perlxstut>,
892 moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to
893 call Perl from C, then read L<perlembed>, L<perlcall>, and
894 L<perlguts>. Don't forget that you can learn a lot from looking at
895 how the authors of existing extension modules wrote their code and
896 solved their problems.
898 =head2 I've read perlembed, perlguts, etc., but I can't embed perl in
899 my C program; what am I doing wrong?
901 Download the ExtUtils::Embed kit from CPAN and run `make test'. If
902 the tests pass, read the pods again and again and again. If they
903 fail, see L<perlbug> and send a bug report with the output of
904 C<make test TEST_VERBOSE=1> along with C<perl -V>.
906 =head2 When I tried to run my script, I got this message. What does it
909 A complete list of Perl's error messages and warnings with explanatory
910 text can be found in L<perldiag>. You can also use the splain program
911 (distributed with Perl) to explain the error messages:
913 perl program 2>diag.out
914 splain [-v] [-p] diag.out
916 or change your program to explain the messages for you:
922 use diagnostics -verbose;
924 =head2 What's MakeMaker?
926 This module (part of the standard Perl distribution) is designed to
927 write a Makefile for an extension module from a Makefile.PL. For more
928 information, see L<ExtUtils::MakeMaker>.
930 =head1 AUTHOR AND COPYRIGHT
932 Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington.
935 This documentation is free; you can redistribute it and/or modify it
936 under the same terms as Perl itself.
938 Irrespective of its distribution, all code examples here are in the public
939 domain. You are permitted and encouraged to use this code and any
940 derivatives thereof in your own programs for fun or for profit as you
941 see fit. A simple comment in the code giving credit to the FAQ would
942 be courteous but is not required.