3 perlfaq3 - Programming Tools ($Revision: 1.38 $, $Date: 1999/05/23 16:08:30 $)
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 man pages? 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 man page 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) man page, 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, no. The Shell.pm module (distributed with Perl) makes
45 Perl try commands which aren't part of the Perl language as shell
46 commands. perlsh from the source distribution is simplistic and
47 uninteresting, but may still be what you want.
49 =head2 How do I debug my Perl programs?
51 Have you tried C<use warnings> or used C<-w>? They enable warnings
52 to detect dubious practices.
54 Have you tried C<use strict>? It prevents you from using symbolic
55 references, makes you predeclare any subroutines that you call as bare
56 words, and (probably most importantly) forces you to predeclare your
57 variables with C<my>, C<our>, or C<use vars>.
59 Did you check the return values of each and every system call? The operating
60 system (and thus Perl) tells you whether they worked, and if not
63 open(FH, "> /etc/cantwrite")
64 or die "Couldn't write to /etc/cantwrite: $!\n";
66 Did you read L<perltrap>? It's full of gotchas for old and new Perl
67 programmers and even has sections for those of you who are upgrading
68 from languages like I<awk> and I<C>.
70 Have you tried the Perl debugger, described in L<perldebug>? You can
71 step through your program and see what it's doing and thus work out
72 why what it's doing isn't what it should be doing.
74 =head2 How do I profile my Perl programs?
76 You should get the Devel::DProf module from the standard distribution
77 (or separately on CPAN) and also use Benchmark.pm from the standard
78 distribution. The Benchmark module lets you time specific portions of
79 your code, while Devel::DProf gives detailed breakdowns of where your
82 Here's a sample use of Benchmark:
86 @junk = `cat /etc/motd`;
90 'map' => sub { my @a = @junk;
94 'for' => sub { my @a = @junk;
100 This is what it prints (on one machine--your results will be dependent
101 on your hardware, operating system, and the load on your machine):
103 Benchmark: timing 10000 iterations of for, map...
104 for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu)
105 map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu)
107 Be aware that a good benchmark is very hard to write. It only tests the
108 data you give it and proves little about the differing complexities
109 of contrasting algorithms.
111 =head2 How do I cross-reference my Perl programs?
113 The B::Xref module, shipped with the new, alpha-release Perl compiler
114 (not the general distribution prior to the 5.005 release), can be used
115 to generate cross-reference reports for Perl programs.
117 perl -MO=Xref[,OPTIONS] scriptname.plx
119 =head2 Is there a pretty-printer (formatter) for Perl?
121 There is no program that will reformat Perl as much as indent(1) does
122 for C. The complex feedback between the scanner and the parser (this
123 feedback is what confuses the vgrind and emacs programs) makes it
124 challenging at best to write a stand-alone Perl parser.
126 Of course, if you simply follow the guidelines in L<perlstyle>, you
127 shouldn't need to reformat. The habit of formatting your code as you
128 write it will help prevent bugs. Your editor can and should help you
129 with this. The perl-mode or newer cperl-mode for emacs can provide
130 remarkable amounts of help with most (but not all) code, and even less
131 programmable editors can provide significant assistance. Tom swears
132 by the following settings in vi and its clones:
137 Now put that in your F<.exrc> file (replacing the caret characters
138 with control characters) and away you go. In insert mode, ^T is
139 for indenting, ^D is for undenting, and ^O is for blockdenting--
140 as it were. If you haven't used the last one, you're missing
141 a lot. A more complete example, with comments, can be found at
142 http://www.perl.com/CPAN-local/authors/id/TOMC/scripts/toms.exrc.gz
144 If you are used to using the I<vgrind> program for printing out nice code
145 to a laser printer, you can take a stab at this using
146 http://www.perl.com/CPAN/doc/misc/tips/working.vgrind.entry, but the
147 results are not particularly satisfying for sophisticated code.
149 The a2ps at http://www.infres.enst.fr/%7Edemaille/a2ps/ does lots of things
150 related to generating nicely printed output of documents.
152 =head2 Is there a ctags for Perl?
154 There's a simple one at
155 http://www.perl.com/CPAN/authors/id/TOMC/scripts/ptags.gz which may do
156 the trick. And if not, it's easy to hack into what you want.
158 =head2 Is there an IDE or Windows Perl Editor?
160 Perl programs are just plain text, so any editor will do.
162 If you're on Unix, you already have an IDE--Unix itself. The UNIX
163 philosophy is the philosophy of several small tools that each do one
164 thing and do it well. It's like a carpenter's toolbox.
166 If you want an IDE, check the following:
172 http://www.codemagiccd.com/
174 Collection of various programming tools for Windows: Perl (5.005_03),
175 TclTk, Python, GNU programming tools, REBOL, wxWindows toolkit, the
176 MinGW GNU C/C++ compiler, DJGPP GNU C/C++ compiler, Cint C
177 interpreter, YaBasic.
181 ActiveState's cross-platform (as of April 2001 Windows and Linux),
182 multi-language IDE has Perl support, including a regular expression
183 debugger and remote debugging
184 (http://www.ActiveState.com/Products/Komodo/index.html). (Visual
185 Perl, a Visual Studio.NET plug-in is currently (early 2001) in beta
186 (http://www.ActiveState.com/Products/VisualPerl/index.html)).
188 =item The Object System
190 (http://www.castlelink.co.uk/object_system/) is a Perl web
191 applications development IDE, apparently for any platform
196 (http://www.solutionsoft.com/perl.htm) is an integrated development
197 environment for Windows that supports Perl development.
199 =item Perl code magic
201 (http://www.petes-place.com/codemagic.html).
205 http://helpconsulting.net/visiperl/, from Help Consulting, for Windows.
209 For editors: if you're on Unix you probably have vi or a vi clone already,
210 and possibly an emacs too, so you may not need to download anything.
211 In any emacs the cperl-mode (M-x cperl-mode) gives you perhaps the
212 best available Perl editing mode in any editor.
214 For Windows editors: you can download an Emacs
220 http://www.gnu.org/software/emacs/windows/ntemacs.html
224 http://members.nbci.com/uemacs/
228 http://www.xemacs.org/Download/index.html
232 or a vi clone such as
238 ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/
248 win32: http://www.cs.vu.nl/%7Etmgil/vi.html
252 For vi lovers in general, Windows or elsewhere:
253 http://www.thomer.com/thomer/vi/vi.html.
255 nvi (http://www.bostic.com/vi/, available from CPAN in src/misc/) is
256 yet another vi clone, unfortunately not available for Windows, but in
257 UNIX platforms you might be interested in trying it out, firstly because
258 strictly speaking it is not a vi clone, it is the real vi, or the new
259 incarnation of it, and secondly because you can embed Perl inside it
260 to use Perl as the scripting language. nvi is not alone in this,
261 though: at least also vim and vile offer an embedded Perl.
263 The following are Win32 multilanguage editor/IDESs that support Perl:
269 http://www.starbase.com/
273 http://www.MultiEdit.com/
277 http://www.slickedit.com/
281 There is also a toyedit Text widget based editor written in Perl
282 that is distributed with the Tk module on CPAN. The ptkdb
283 (http://world.std.com/~aep/ptkdb/) is a Perl/tk based debugger that
284 acts as a development environment of sorts. Perl Composer
285 (http://perlcomposer.sourceforge.net/vperl.html) is an IDE for Perl/Tk
288 In addition to an editor/IDE you might be interested in a more
289 powerful shell environment for Win32. Your options include
295 from the Cygwin package (http://sources.redhat.com/cygwin/)
299 from the MKS Toolkit (http://www.mks.com/), or the Bourne shell of
300 the U/WIN environment (http://www.research.att.com/sw/tools/uwin/)
304 ftp://ftp.astron.com/pub/tcsh/, see also
305 http://www.primate.wisc.edu/software/csh-tcsh-book/
309 ftp://ftp.blarg.net/users/amol/zsh/, see also http://www.zsh.org/
313 MKS and U/WIN are commercial (U/WIN is free for educational and
314 research purposes), Cygwin is covered by the GNU Public License (but
315 that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all
316 contain (in addition to the shells) a comprehensive set of standard
317 UNIX toolkit utilities.
319 If you're transferring text files between Unix and Windows using FTP
320 be sure to transfer them in ASCII mode so the ends of lines are
321 appropriately converted.
323 On Mac OS the MacPerl Application comes with a simple 32k text editor
324 that behaves like a rudimentary IDE. In contrast to the MacPerl Application
325 the MPW Perl tool can make use of the MPW Shell itself as an editor (with
330 =item BBEdit and BBEdit Lite
332 are text editors for Mac OS that have a Perl sensitivity mode
333 (http://web.barebones.com/).
337 is an editor, written and extensible in Tcl, that nonetheless has
338 built in support for several popular markup and programming languages
339 including Perl and HTML (http://alpha.olm.net/).
343 Pepper and Pe are programming language sensitive text editors for Mac
344 OS X and BeOS respectively (http://www.hekkelman.com/).
346 =head2 Where can I get Perl macros for vi?
348 For a complete version of Tom Christiansen's vi configuration file,
349 see http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc.gz ,
350 the standard benchmark file for vi emulators. The file runs best with nvi,
351 the current version of vi out of Berkeley, which incidentally can be built
352 with an embedded Perl interpreter--see http://www.perl.com/CPAN/src/misc.
354 =head2 Where can I get perl-mode for emacs?
356 Since Emacs version 19 patchlevel 22 or so, there have been both a
357 perl-mode.el and support for the Perl debugger built in. These should
358 come with the standard Emacs 19 distribution.
360 In the Perl source directory, you'll find a directory called "emacs",
361 which contains a cperl-mode that color-codes keywords, provides
362 context-sensitive help, and other nifty things.
364 Note that the perl-mode of emacs will have fits with C<"main'foo">
365 (single quote), and mess up the indentation and highlighting. You
366 are probably using C<"main::foo"> in new Perl code anyway, so this
367 shouldn't be an issue.
369 =head2 How can I use curses with Perl?
371 The Curses module from CPAN provides a dynamically loadable object
372 module interface to a curses library. A small demo can be found at the
373 directory http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep;
374 this program repeats a command and updates the screen as needed, rendering
375 B<rep ps axu> similar to B<top>.
377 =head2 How can I use X or Tk with Perl?
379 Tk is a completely Perl-based, object-oriented interface to the Tk toolkit
380 that doesn't force you to use Tcl just to get at Tk. Sx is an interface
381 to the Athena Widget set. Both are available from CPAN. See the
382 directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/
384 Invaluable for Perl/Tk programming are the Perl/Tk FAQ at
385 http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference
387 http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ , and the
389 http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html .
391 =head2 How can I generate simple menus without using CGI or Tk?
393 The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
394 module, which is curses-based, can help with this.
396 =head2 What is undump?
398 See the next question on ``How can I make my Perl program run faster?''
400 =head2 How can I make my Perl program run faster?
402 The best way to do this is to come up with a better algorithm. This
403 can often make a dramatic difference. Jon Bentley's book
404 ``Programming Pearls'' (that's not a misspelling!) has some good tips
405 on optimization, too. Advice on benchmarking boils down to: benchmark
406 and profile to make sure you're optimizing the right part, look for
407 better algorithms instead of microtuning your code, and when all else
408 fails consider just buying faster hardware.
410 A different approach is to autoload seldom-used Perl code. See the
411 AutoSplit and AutoLoader modules in the standard distribution for
412 that. Or you could locate the bottleneck and think about writing just
413 that part in C, the way we used to take bottlenecks in C code and
414 write them in assembler. Similar to rewriting in C,
415 modules that have critical sections can be written in C (for instance, the
416 PDL module from CPAN).
418 In some cases, it may be worth it to use the backend compiler to
419 produce byte code (saving compilation time) or compile into C, which
420 will certainly save compilation time and sometimes a small amount (but
421 not much) execution time. See the question about compiling your Perl
422 programs for more on the compiler--the wins aren't as obvious as you'd
425 If you're currently linking your perl executable to a shared I<libc.so>,
426 you can often gain a 10-25% performance benefit by rebuilding it to
427 link with a static libc.a instead. This will make a bigger perl
428 executable, but your Perl programs (and programmers) may thank you for
429 it. See the F<INSTALL> file in the source distribution for more
432 Unsubstantiated reports allege that Perl interpreters that use sfio
433 outperform those that don't (for I/O intensive applications). To try
434 this, see the F<INSTALL> file in the source distribution, especially
435 the ``Selecting File I/O mechanisms'' section.
437 The undump program was an old attempt to speed up your Perl program
438 by storing the already-compiled form to disk. This is no longer
439 a viable option, as it only worked on a few architectures, and
440 wasn't a good solution anyway.
442 =head2 How can I make my Perl program take less memory?
444 When it comes to time-space tradeoffs, Perl nearly always prefers to
445 throw memory at a problem. Scalars in Perl use more memory than
446 strings in C, arrays take more than that, and hashes use even more. While
447 there's still a lot to be done, recent releases have been addressing
448 these issues. For example, as of 5.004, duplicate hash keys are
449 shared amongst all hashes using them, so require no reallocation.
451 In some cases, using substr() or vec() to simulate arrays can be
452 highly beneficial. For example, an array of a thousand booleans will
453 take at least 20,000 bytes of space, but it can be turned into one
454 125-byte bit vector--a considerable memory savings. The standard
455 Tie::SubstrHash module can also help for certain types of data
456 structure. If you're working with specialist data structures
457 (matrices, for instance) modules that implement these in C may use
458 less memory than equivalent Perl modules.
460 Another thing to try is learning whether your Perl was compiled with
461 the system malloc or with Perl's builtin malloc. Whichever one it
462 is, try using the other one and see whether this makes a difference.
463 Information about malloc is in the F<INSTALL> file in the source
464 distribution. You can find out whether you are using perl's malloc by
465 typing C<perl -V:usemymalloc>.
467 =head2 Is it unsafe to return a pointer to local data?
469 No, Perl's garbage collection system takes care of this.
477 push @many, makeone();
480 print $many[4][5], "\n";
484 =head2 How can I free an array or hash so my program shrinks?
486 You can't. On most operating systems, memory allocated to a program
487 can never be returned to the system. That's why long-running programs
488 sometimes re-exec themselves. Some operating systems (notably,
489 FreeBSD and Linux) allegedly reclaim large chunks of memory that is no
490 longer used, but it doesn't appear to happen with Perl (yet). The Mac
491 appears to be the only platform that will reliably (albeit, slowly)
492 return memory to the OS.
494 We've had reports that on Linux (Redhat 5.1) on Intel, C<undef
495 $scalar> will return memory to the system, while on Solaris 2.6 it
496 won't. In general, try it yourself and see.
498 However, judicious use of my() on your variables will help make sure
499 that they go out of scope so that Perl can free up that space for
500 use in other parts of your program. A global variable, of course, never
501 goes out of scope, so you can't get its space automatically reclaimed,
502 although undef()ing and/or delete()ing it will achieve the same effect.
503 In general, memory allocation and de-allocation isn't something you can
504 or should be worrying about much in Perl, but even this capability
505 (preallocation of data types) is in the works.
507 =head2 How can I make my CGI script more efficient?
509 Beyond the normal measures described to make general Perl programs
510 faster or smaller, a CGI program has additional issues. It may be run
511 several times per second. Given that each time it runs it will need
512 to be re-compiled and will often allocate a megabyte or more of system
513 memory, this can be a killer. Compiling into C B<isn't going to help
514 you> because the process start-up overhead is where the bottleneck is.
516 There are two popular ways to avoid this overhead. One solution
517 involves running the Apache HTTP server (available from
518 http://www.apache.org/) with either of the mod_perl or mod_fastcgi
521 With mod_perl and the Apache::Registry module (distributed with
522 mod_perl), httpd will run with an embedded Perl interpreter which
523 pre-compiles your script and then executes it within the same address
524 space without forking. The Apache extension also gives Perl access to
525 the internal server API, so modules written in Perl can do just about
526 anything a module written in C can. For more on mod_perl, see
527 http://perl.apache.org/
529 With the FCGI module (from CPAN) and the mod_fastcgi
530 module (available from http://www.fastcgi.com/) each of your Perl
531 programs becomes a permanent CGI daemon process.
533 Both of these solutions can have far-reaching effects on your system
534 and on the way you write your CGI programs, so investigate them with
537 See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
539 A non-free, commercial product, ``The Velocity Engine for Perl'',
540 (http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ )
541 might also be worth looking at. It will allow you to increase the
542 performance of your Perl programs, running programs up to 25 times
543 faster than normal CGI Perl when running in persistent Perl mode or 4
544 to 5 times faster without any modification to your existing CGI
545 programs. Fully functional evaluation copies are available from the
548 =head2 How can I hide the source for my Perl program?
550 Delete it. :-) Seriously, there are a number of (mostly
551 unsatisfactory) solutions with varying levels of ``security''.
553 First of all, however, you I<can't> take away read permission, because
554 the source code has to be readable in order to be compiled and
555 interpreted. (That doesn't mean that a CGI script's source is
556 readable by people on the web, though--only by people with access to
557 the filesystem.) So you have to leave the permissions at the socially
560 Some people regard this as a security problem. If your program does
561 insecure things and relies on people not knowing how to exploit those
562 insecurities, it is not secure. It is often possible for someone to
563 determine the insecure things and exploit them without viewing the
564 source. Security through obscurity, the name for hiding your bugs
565 instead of fixing them, is little security indeed.
567 You can try using encryption via source filters (Starting from Perl
568 5.8 the Filter::Simple and Filter::Util::Call modules are included in
569 the standard distribution), but any decent programmer will be able to
570 decrypt it. You can try using the byte code compiler and interpreter
571 described below, but the curious might still be able to de-compile it.
572 You can try using the native-code compiler described below, but
573 crackers might be able to disassemble it. These pose varying degrees
574 of difficulty to people wanting to get at your code, but none can
575 definitively conceal it (true of every language, not just Perl).
577 If you're concerned about people profiting from your code, then the
578 bottom line is that nothing but a restrictive license will give you
579 legal security. License your software and pepper it with threatening
580 statements like ``This is unpublished proprietary software of XYZ Corp.
581 Your access to it does not give you permission to use it blah blah
582 blah.'' We are not lawyers, of course, so you should see a lawyer if
583 you want to be sure your license's wording will stand up in court.
585 =head2 How can I compile my Perl program into byte code or C?
587 Malcolm Beattie has written a multifunction backend compiler,
588 available from CPAN, that can do both these things. It is included
589 in the perl5.005 release, but is still considered experimental.
590 This means it's fun to play with if you're a programmer but not
591 really for people looking for turn-key solutions.
593 Merely compiling into C does not in and of itself guarantee that your
594 code will run very much faster. That's because except for lucky cases
595 where a lot of native type inferencing is possible, the normal Perl
596 run-time system is still present and so your program will take just as
597 long to run and be just as big. Most programs save little more than
598 compilation time, leaving execution no more than 10-30% faster. A few
599 rare programs actually benefit significantly (even running several times
600 faster), but this takes some tweaking of your code.
602 You'll probably be astonished to learn that the current version of the
603 compiler generates a compiled form of your script whose executable is
604 just as big as the original perl executable, and then some. That's
605 because as currently written, all programs are prepared for a full
606 eval() statement. You can tremendously reduce this cost by building a
607 shared I<libperl.so> library and linking against that. See the
608 F<INSTALL> podfile in the Perl source distribution for details. If
609 you link your main perl binary with this, it will make it minuscule.
610 For example, on one author's system, F</usr/bin/perl> is only 11k in
613 In general, the compiler will do nothing to make a Perl program smaller,
614 faster, more portable, or more secure. In fact, it can make your
615 situation worse. The executable will be bigger, your VM system may take
616 longer to load the whole thing, the binary is fragile and hard to fix,
617 and compilation never stopped software piracy in the form of crackers,
618 viruses, or bootleggers. The real advantage of the compiler is merely
619 packaging, and once you see the size of what it makes (well, unless
620 you use a shared I<libperl.so>), you'll probably want a complete
623 =head2 How can I compile Perl into Java?
625 You can also integrate Java and Perl with the
626 Perl Resource Kit from O'Reilly and Associates. See
627 http://www.oreilly.com/catalog/prkunix/ .
629 Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in
630 development, allows Perl code to be called from Java. See jpl/README
631 in the Perl source tree.
633 =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
637 extproc perl -S -your_switches
639 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
640 `extproc' handling). For DOS one should first invent a corresponding
641 batch file and codify it in C<ALTERNATIVE_SHEBANG> (see the
642 F<INSTALL> file in the source distribution for more information).
644 The Win95/NT installation, when using the ActiveState port of Perl,
645 will modify the Registry to associate the C<.pl> extension with the
646 perl interpreter. If you install another port, perhaps even building
647 your own Win95/NT Perl from the standard sources by using a Windows port
648 of gcc (e.g., with cygwin or mingw32), then you'll have to modify
649 the Registry yourself. In addition to associating C<.pl> with the
650 interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them
651 run the program C<install-linux.pl> merely by typing C<install-linux>.
653 Macintosh Perl programs will have the appropriate Creator and
654 Type, so that double-clicking them will invoke the Perl application.
656 I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
657 throw the perl interpreter into your cgi-bin directory, in order to
658 get your programs working for a web server. This is an EXTREMELY big
659 security risk. Take the time to figure out how to do it correctly.
661 =head2 Can I write useful Perl programs on the command line?
663 Yes. Read L<perlrun> for more information. Some examples follow.
664 (These assume standard Unix shell quoting rules.)
666 # sum first and last fields
667 perl -lane 'print $F[0] + $F[-1]' *
669 # identify text files
670 perl -le 'for(@ARGV) {print if -f && -T _}' *
672 # remove (most) comments from C program
673 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
675 # make file a month younger than today, defeating reaper daemons
676 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
678 # find first unused uid
679 perl -le '$i++ while getpwuid($i); print $i'
681 # display reasonable manpath
682 echo $PATH | perl -nl -072 -e '
683 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
685 OK, the last one was actually an Obfuscated Perl Contest entry. :-)
687 =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system?
689 The problem is usually that the command interpreters on those systems
690 have rather different ideas about quoting than the Unix shells under
691 which the one-liners were created. On some systems, you may have to
692 change single-quotes to double ones, which you must I<NOT> do on Unix
693 or Plan9 systems. You might also have to change a single % to a %%.
698 perl -e 'print "Hello world\n"'
701 perl -e "print \"Hello world\n\""
704 print "Hello world\n"
705 (then Run "Myscript" or Shift-Command-R)
708 perl -e "print ""Hello world\n"""
710 The problem is that none of these examples are reliable: they depend on the
711 command interpreter. Under Unix, the first two often work. Under DOS,
712 it's entirely possible that neither works. If 4DOS was the command shell,
713 you'd probably have better luck like this:
715 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
717 Under the Mac, it depends which environment you are using. The MacPerl
718 shell, or MPW, is much like Unix shells in its support for several
719 quoting variants, except that it makes free use of the Mac's non-ASCII
720 characters as control characters.
722 Using qq(), q(), and qx(), instead of "double quotes", 'single
723 quotes', and `backticks`, may make one-liners easier to write.
725 There is no general solution to all of this. It is a mess, pure and
726 simple. Sucks to be away from Unix, huh? :-)
728 [Some of this answer was contributed by Kenneth Albanowski.]
730 =head2 Where can I learn about CGI or Web programming in Perl?
732 For modules, get the CGI or LWP modules from CPAN. For textbooks,
733 see the two especially dedicated to web stuff in the question on
734 books. For problems and questions related to the web, like ``Why
735 do I get 500 Errors'' or ``Why doesn't it run from the browser right
736 when it runs fine on the command line'', see these sources:
739 http://www.w3.org/Security/Faq/
742 http://www.boutell.com/faq/
745 http://www.webthing.com/tutorials/cgifaq.html
748 http://www.w3.org/pub/WWW/Protocols/HTTP/
751 http://www.w3.org/TR/REC-html40/
752 http://www.w3.org/pub/WWW/MarkUp/
755 http://www.w3.org/CGI/
758 http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt
760 =head2 Where can I learn about object-oriented Perl programming?
762 A good place to start is L<perltoot>, and you can use L<perlobj>,
763 L<perlboot>, and L<perlbot> for reference. Perltoot didn't come out
764 until the 5.004 release; you can get a copy (in pod, html, or
765 postscript) from http://www.perl.com/CPAN/doc/FMTEYEWTK/ .
767 =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp]
769 If you want to call C from Perl, start with L<perlxstut>,
770 moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to
771 call Perl from C, then read L<perlembed>, L<perlcall>, and
772 L<perlguts>. Don't forget that you can learn a lot from looking at
773 how the authors of existing extension modules wrote their code and
774 solved their problems.
776 =head2 I've read perlembed, perlguts, etc., but I can't embed perl in
777 my C program; what am I doing wrong?
779 Download the ExtUtils::Embed kit from CPAN and run `make test'. If
780 the tests pass, read the pods again and again and again. If they
781 fail, see L<perlbug> and send a bug report with the output of
782 C<make test TEST_VERBOSE=1> along with C<perl -V>.
784 =head2 When I tried to run my script, I got this message. What does it
787 A complete list of Perl's error messages and warnings with explanatory
788 text can be found in L<perldiag>. You can also use the splain program
789 (distributed with Perl) to explain the error messages:
791 perl program 2>diag.out
792 splain [-v] [-p] diag.out
794 or change your program to explain the messages for you:
800 use diagnostics -verbose;
802 =head2 What's MakeMaker?
804 This module (part of the standard Perl distribution) is designed to
805 write a Makefile for an extension module from a Makefile.PL. For more
806 information, see L<ExtUtils::MakeMaker>.
808 =head1 AUTHOR AND COPYRIGHT
810 Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington.
813 When included as an integrated part of the Standard Distribution
814 of Perl or of its documentation (printed or otherwise), this works is
815 covered under Perl's Artistic License. For separate distributions of
816 all or part of this FAQ outside of that, see L<perlfaq>.
818 Irrespective of its distribution, all code examples here are in the public
819 domain. You are permitted and encouraged to use this code and any
820 derivatives thereof in your own programs for fun or for profit as you
821 see fit. A simple comment in the code giving credit to the FAQ would
822 be courteous but is not required.