3 perlfaq3 - Programming Tools ($Revision: 1.4 $, $Date: 2001/10/02 19:42:02 $)
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 There's a simple one at
168 http://www.perl.com/CPAN/authors/id/TOMC/scripts/ptags.gz which may do
169 the trick. And if not, it's easy to hack 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 For Windows editors: you can download an Emacs
241 http://www.gnu.org/software/emacs/windows/ntemacs.html
245 http://members.nbci.com/uemacs/
249 http://www.xemacs.org/Download/index.html
253 or a vi clone such as
259 ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/
269 win32: http://www.cs.vu.nl/%7Etmgil/vi.html
273 For vi lovers in general, Windows or elsewhere:
274 http://www.thomer.com/thomer/vi/vi.html.
276 nvi (http://www.bostic.com/vi/, available from CPAN in src/misc/) is
277 yet another vi clone, unfortunately not available for Windows, but in
278 UNIX platforms you might be interested in trying it out, firstly because
279 strictly speaking it is not a vi clone, it is the real vi, or the new
280 incarnation of it, and secondly because you can embed Perl inside it
281 to use Perl as the scripting language. nvi is not alone in this,
282 though: at least also vim and vile offer an embedded Perl.
284 The following are Win32 multilanguage editor/IDESs that support Perl:
290 http://www.starbase.com/
294 http://www.MultiEdit.com/
298 http://www.slickedit.com/
302 There is also a toyedit Text widget based editor written in Perl
303 that is distributed with the Tk module on CPAN. The ptkdb
304 (http://world.std.com/~aep/ptkdb/) is a Perl/tk based debugger that
305 acts as a development environment of sorts. Perl Composer
306 (http://perlcomposer.sourceforge.net/vperl.html) is an IDE for Perl/Tk
309 In addition to an editor/IDE you might be interested in a more
310 powerful shell environment for Win32. Your options include
316 from the Cygwin package (http://sources.redhat.com/cygwin/)
320 from the MKS Toolkit (http://www.mks.com/), or the Bourne shell of
321 the U/WIN environment (http://www.research.att.com/sw/tools/uwin/)
325 ftp://ftp.astron.com/pub/tcsh/, see also
326 http://www.primate.wisc.edu/software/csh-tcsh-book/
330 ftp://ftp.blarg.net/users/amol/zsh/, see also http://www.zsh.org/
334 MKS and U/WIN are commercial (U/WIN is free for educational and
335 research purposes), Cygwin is covered by the GNU Public License (but
336 that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all
337 contain (in addition to the shells) a comprehensive set of standard
338 UNIX toolkit utilities.
340 If you're transferring text files between Unix and Windows using FTP
341 be sure to transfer them in ASCII mode so the ends of lines are
342 appropriately converted.
344 On Mac OS the MacPerl Application comes with a simple 32k text editor
345 that behaves like a rudimentary IDE. In contrast to the MacPerl Application
346 the MPW Perl tool can make use of the MPW Shell itself as an editor (with
351 =item BBEdit and BBEdit Lite
353 are text editors for Mac OS that have a Perl sensitivity mode
354 (http://web.barebones.com/).
358 is an editor, written and extensible in Tcl, that nonetheless has
359 built in support for several popular markup and programming languages
360 including Perl and HTML (http://alpha.olm.net/).
364 Pepper and Pe are programming language sensitive text editors for Mac
365 OS X and BeOS respectively (http://www.hekkelman.com/).
367 =head2 Where can I get Perl macros for vi?
369 For a complete version of Tom Christiansen's vi configuration file,
370 see http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc.gz ,
371 the standard benchmark file for vi emulators. The file runs best with nvi,
372 the current version of vi out of Berkeley, which incidentally can be built
373 with an embedded Perl interpreter--see http://www.perl.com/CPAN/src/misc.
375 =head2 Where can I get perl-mode for emacs?
377 Since Emacs version 19 patchlevel 22 or so, there have been both a
378 perl-mode.el and support for the Perl debugger built in. These should
379 come with the standard Emacs 19 distribution.
381 In the Perl source directory, you'll find a directory called "emacs",
382 which contains a cperl-mode that color-codes keywords, provides
383 context-sensitive help, and other nifty things.
385 Note that the perl-mode of emacs will have fits with C<"main'foo">
386 (single quote), and mess up the indentation and highlighting. You
387 are probably using C<"main::foo"> in new Perl code anyway, so this
388 shouldn't be an issue.
390 =head2 How can I use curses with Perl?
392 The Curses module from CPAN provides a dynamically loadable object
393 module interface to a curses library. A small demo can be found at the
394 directory http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep;
395 this program repeats a command and updates the screen as needed, rendering
396 B<rep ps axu> similar to B<top>.
398 =head2 How can I use X or Tk with Perl?
400 Tk is a completely Perl-based, object-oriented interface to the Tk toolkit
401 that doesn't force you to use Tcl just to get at Tk. Sx is an interface
402 to the Athena Widget set. Both are available from CPAN. See the
403 directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/
405 Invaluable for Perl/Tk programming are the Perl/Tk FAQ at
406 http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference
408 http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ , and the
410 http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html .
412 =head2 How can I generate simple menus without using CGI or Tk?
414 The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
415 module, which is curses-based, can help with this.
417 =head2 What is undump?
419 See the next question on ``How can I make my Perl program run faster?''
421 =head2 How can I make my Perl program run faster?
423 The best way to do this is to come up with a better algorithm. This
424 can often make a dramatic difference. Jon Bentley's book
425 ``Programming Pearls'' (that's not a misspelling!) has some good tips
426 on optimization, too. Advice on benchmarking boils down to: benchmark
427 and profile to make sure you're optimizing the right part, look for
428 better algorithms instead of microtuning your code, and when all else
429 fails consider just buying faster hardware. You will probably want to
430 read the answer to the earlier question ``How do I profile my Perl programs?''
431 if you haven't done so already.
433 A different approach is to autoload seldom-used Perl code. See the
434 AutoSplit and AutoLoader modules in the standard distribution for
435 that. Or you could locate the bottleneck and think about writing just
436 that part in C, the way we used to take bottlenecks in C code and
437 write them in assembler. Similar to rewriting in C,
438 modules that have critical sections can be written in C (for instance, the
439 PDL module from CPAN).
441 In some cases, it may be worth it to use the backend compiler to
442 produce byte code (saving compilation time) or compile into C, which
443 will certainly save compilation time and sometimes a small amount (but
444 not much) execution time. See the question about compiling your Perl
445 programs for more on the compiler--the wins aren't as obvious as you'd
448 If you're currently linking your perl executable to a shared I<libc.so>,
449 you can often gain a 10-25% performance benefit by rebuilding it to
450 link with a static libc.a instead. This will make a bigger perl
451 executable, but your Perl programs (and programmers) may thank you for
452 it. See the F<INSTALL> file in the source distribution for more
455 Unsubstantiated reports allege that Perl interpreters that use sfio
456 outperform those that don't (for I/O intensive applications). To try
457 this, see the F<INSTALL> file in the source distribution, especially
458 the ``Selecting File I/O mechanisms'' section.
460 The undump program was an old attempt to speed up your Perl program
461 by storing the already-compiled form to disk. This is no longer
462 a viable option, as it only worked on a few architectures, and
463 wasn't a good solution anyway.
465 =head2 How can I make my Perl program take less memory?
467 When it comes to time-space tradeoffs, Perl nearly always prefers to
468 throw memory at a problem. Scalars in Perl use more memory than
469 strings in C, arrays take more than that, and hashes use even more. While
470 there's still a lot to be done, recent releases have been addressing
471 these issues. For example, as of 5.004, duplicate hash keys are
472 shared amongst all hashes using them, so require no reallocation.
474 In some cases, using substr() or vec() to simulate arrays can be
475 highly beneficial. For example, an array of a thousand booleans will
476 take at least 20,000 bytes of space, but it can be turned into one
477 125-byte bit vector--a considerable memory savings. The standard
478 Tie::SubstrHash module can also help for certain types of data
479 structure. If you're working with specialist data structures
480 (matrices, for instance) modules that implement these in C may use
481 less memory than equivalent Perl modules.
483 Another thing to try is learning whether your Perl was compiled with
484 the system malloc or with Perl's builtin malloc. Whichever one it
485 is, try using the other one and see whether this makes a difference.
486 Information about malloc is in the F<INSTALL> file in the source
487 distribution. You can find out whether you are using perl's malloc by
488 typing C<perl -V:usemymalloc>.
490 Of course, the best way to save memory is to not do anything to waste
491 it in the first place. Good programming practices can go a long way
498 Don't read an entire file into memory if you can process it line
499 by line. Or more concretely, use a loop like this:
518 When the files you're processing are small, it doesn't much matter which
519 way you do it, but it makes a huge difference when they start getting
522 =item * Pass by reference
524 Pass arrays and hashes by reference, not by value. For one thing, it's
525 the only way to pass multiple lists or hashes (or both) in a single
526 call/return. It also avoids creating a copy of all the contents. This
527 requires some judgment, however, because any changes will be propagated
528 back to the original data. If you really want to mangle (er, modify) a
529 copy, you'll have to sacrifice the memory needed to make one.
531 =item * Tie large variables to disk.
533 For "big" data stores (i.e. ones that exceed available memory) consider
534 using one of the DB modules to store it on disk instead of in RAM. This
535 will incur a penalty in access time, but that's probably better that
536 causing your hard disk to thrash due to massive swapping.
540 =head2 Is it unsafe to return a pointer to local data?
542 No, Perl's garbage collection system takes care of this.
550 push @many, makeone();
553 print $many[4][5], "\n";
557 =head2 How can I free an array or hash so my program shrinks?
559 You can't. On most operating systems, memory allocated to a program
560 can never be returned to the system. That's why long-running programs
561 sometimes re-exec themselves. Some operating systems (notably,
562 FreeBSD and Linux) allegedly reclaim large chunks of memory that is no
563 longer used, but it doesn't appear to happen with Perl (yet). The Mac
564 appears to be the only platform that will reliably (albeit, slowly)
565 return memory to the OS.
567 We've had reports that on Linux (Redhat 5.1) on Intel, C<undef
568 $scalar> will return memory to the system, while on Solaris 2.6 it
569 won't. In general, try it yourself and see.
571 However, judicious use of my() on your variables will help make sure
572 that they go out of scope so that Perl can free up that space for
573 use in other parts of your program. A global variable, of course, never
574 goes out of scope, so you can't get its space automatically reclaimed,
575 although undef()ing and/or delete()ing it will achieve the same effect.
576 In general, memory allocation and de-allocation isn't something you can
577 or should be worrying about much in Perl, but even this capability
578 (preallocation of data types) is in the works.
580 =head2 How can I make my CGI script more efficient?
582 Beyond the normal measures described to make general Perl programs
583 faster or smaller, a CGI program has additional issues. It may be run
584 several times per second. Given that each time it runs it will need
585 to be re-compiled and will often allocate a megabyte or more of system
586 memory, this can be a killer. Compiling into C B<isn't going to help
587 you> because the process start-up overhead is where the bottleneck is.
589 There are two popular ways to avoid this overhead. One solution
590 involves running the Apache HTTP server (available from
591 http://www.apache.org/) with either of the mod_perl or mod_fastcgi
594 With mod_perl and the Apache::Registry module (distributed with
595 mod_perl), httpd will run with an embedded Perl interpreter which
596 pre-compiles your script and then executes it within the same address
597 space without forking. The Apache extension also gives Perl access to
598 the internal server API, so modules written in Perl can do just about
599 anything a module written in C can. For more on mod_perl, see
600 http://perl.apache.org/
602 With the FCGI module (from CPAN) and the mod_fastcgi
603 module (available from http://www.fastcgi.com/) each of your Perl
604 programs becomes a permanent CGI daemon process.
606 Both of these solutions can have far-reaching effects on your system
607 and on the way you write your CGI programs, so investigate them with
610 See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
612 A non-free, commercial product, ``The Velocity Engine for Perl'',
613 (http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ )
614 might also be worth looking at. It will allow you to increase the
615 performance of your Perl programs, running programs up to 25 times
616 faster than normal CGI Perl when running in persistent Perl mode or 4
617 to 5 times faster without any modification to your existing CGI
618 programs. Fully functional evaluation copies are available from the
621 =head2 How can I hide the source for my Perl program?
623 Delete it. :-) Seriously, there are a number of (mostly
624 unsatisfactory) solutions with varying levels of ``security''.
626 First of all, however, you I<can't> take away read permission, because
627 the source code has to be readable in order to be compiled and
628 interpreted. (That doesn't mean that a CGI script's source is
629 readable by people on the web, though--only by people with access to
630 the filesystem.) So you have to leave the permissions at the socially
633 Some people regard this as a security problem. If your program does
634 insecure things and relies on people not knowing how to exploit those
635 insecurities, it is not secure. It is often possible for someone to
636 determine the insecure things and exploit them without viewing the
637 source. Security through obscurity, the name for hiding your bugs
638 instead of fixing them, is little security indeed.
640 You can try using encryption via source filters (Starting from Perl
641 5.8 the Filter::Simple and Filter::Util::Call modules are included in
642 the standard distribution), but any decent programmer will be able to
643 decrypt it. You can try using the byte code compiler and interpreter
644 described below, but the curious might still be able to de-compile it.
645 You can try using the native-code compiler described below, but
646 crackers might be able to disassemble it. These pose varying degrees
647 of difficulty to people wanting to get at your code, but none can
648 definitively conceal it (true of every language, not just Perl).
650 If you're concerned about people profiting from your code, then the
651 bottom line is that nothing but a restrictive license will give you
652 legal security. License your software and pepper it with threatening
653 statements like ``This is unpublished proprietary software of XYZ Corp.
654 Your access to it does not give you permission to use it blah blah
655 blah.'' We are not lawyers, of course, so you should see a lawyer if
656 you want to be sure your license's wording will stand up in court.
658 =head2 How can I compile my Perl program into byte code or C?
660 Malcolm Beattie has written a multifunction backend compiler,
661 available from CPAN, that can do both these things. It is included
662 in the perl5.005 release, but is still considered experimental.
663 This means it's fun to play with if you're a programmer but not
664 really for people looking for turn-key solutions.
666 Merely compiling into C does not in and of itself guarantee that your
667 code will run very much faster. That's because except for lucky cases
668 where a lot of native type inferencing is possible, the normal Perl
669 run-time system is still present and so your program will take just as
670 long to run and be just as big. Most programs save little more than
671 compilation time, leaving execution no more than 10-30% faster. A few
672 rare programs actually benefit significantly (even running several times
673 faster), but this takes some tweaking of your code.
675 You'll probably be astonished to learn that the current version of the
676 compiler generates a compiled form of your script whose executable is
677 just as big as the original perl executable, and then some. That's
678 because as currently written, all programs are prepared for a full
679 eval() statement. You can tremendously reduce this cost by building a
680 shared I<libperl.so> library and linking against that. See the
681 F<INSTALL> podfile in the Perl source distribution for details. If
682 you link your main perl binary with this, it will make it minuscule.
683 For example, on one author's system, F</usr/bin/perl> is only 11k in
686 In general, the compiler will do nothing to make a Perl program smaller,
687 faster, more portable, or more secure. In fact, it can make your
688 situation worse. The executable will be bigger, your VM system may take
689 longer to load the whole thing, the binary is fragile and hard to fix,
690 and compilation never stopped software piracy in the form of crackers,
691 viruses, or bootleggers. The real advantage of the compiler is merely
692 packaging, and once you see the size of what it makes (well, unless
693 you use a shared I<libperl.so>), you'll probably want a complete
696 =head2 How can I compile Perl into Java?
698 You can also integrate Java and Perl with the
699 Perl Resource Kit from O'Reilly and Associates. See
700 http://www.oreilly.com/catalog/prkunix/ .
702 Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in
703 development, allows Perl code to be called from Java. See jpl/README
704 in the Perl source tree.
706 =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
710 extproc perl -S -your_switches
712 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
713 `extproc' handling). For DOS one should first invent a corresponding
714 batch file and codify it in C<ALTERNATIVE_SHEBANG> (see the
715 F<INSTALL> file in the source distribution for more information).
717 The Win95/NT installation, when using the ActiveState port of Perl,
718 will modify the Registry to associate the C<.pl> extension with the
719 perl interpreter. If you install another port, perhaps even building
720 your own Win95/NT Perl from the standard sources by using a Windows port
721 of gcc (e.g., with cygwin or mingw32), then you'll have to modify
722 the Registry yourself. In addition to associating C<.pl> with the
723 interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them
724 run the program C<install-linux.pl> merely by typing C<install-linux>.
726 Macintosh Perl programs will have the appropriate Creator and
727 Type, so that double-clicking them will invoke the Perl application.
729 I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
730 throw the perl interpreter into your cgi-bin directory, in order to
731 get your programs working for a web server. This is an EXTREMELY big
732 security risk. Take the time to figure out how to do it correctly.
734 =head2 Can I write useful Perl programs on the command line?
736 Yes. Read L<perlrun> for more information. Some examples follow.
737 (These assume standard Unix shell quoting rules.)
739 # sum first and last fields
740 perl -lane 'print $F[0] + $F[-1]' *
742 # identify text files
743 perl -le 'for(@ARGV) {print if -f && -T _}' *
745 # remove (most) comments from C program
746 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
748 # make file a month younger than today, defeating reaper daemons
749 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
751 # find first unused uid
752 perl -le '$i++ while getpwuid($i); print $i'
754 # display reasonable manpath
755 echo $PATH | perl -nl -072 -e '
756 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
758 OK, the last one was actually an Obfuscated Perl Contest entry. :-)
760 =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system?
762 The problem is usually that the command interpreters on those systems
763 have rather different ideas about quoting than the Unix shells under
764 which the one-liners were created. On some systems, you may have to
765 change single-quotes to double ones, which you must I<NOT> do on Unix
766 or Plan9 systems. You might also have to change a single % to a %%.
771 perl -e 'print "Hello world\n"'
774 perl -e "print \"Hello world\n\""
777 print "Hello world\n"
778 (then Run "Myscript" or Shift-Command-R)
781 perl -e "print ""Hello world\n"""
783 The problem is that none of these examples are reliable: they depend on the
784 command interpreter. Under Unix, the first two often work. Under DOS,
785 it's entirely possible that neither works. If 4DOS was the command shell,
786 you'd probably have better luck like this:
788 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
790 Under the Mac, it depends which environment you are using. The MacPerl
791 shell, or MPW, is much like Unix shells in its support for several
792 quoting variants, except that it makes free use of the Mac's non-ASCII
793 characters as control characters.
795 Using qq(), q(), and qx(), instead of "double quotes", 'single
796 quotes', and `backticks`, may make one-liners easier to write.
798 There is no general solution to all of this. It is a mess, pure and
799 simple. Sucks to be away from Unix, huh? :-)
801 [Some of this answer was contributed by Kenneth Albanowski.]
803 =head2 Where can I learn about CGI or Web programming in Perl?
805 For modules, get the CGI or LWP modules from CPAN. For textbooks,
806 see the two especially dedicated to web stuff in the question on
807 books. For problems and questions related to the web, like ``Why
808 do I get 500 Errors'' or ``Why doesn't it run from the browser right
809 when it runs fine on the command line'', see these sources:
812 http://www.w3.org/Security/Faq/
815 http://www.boutell.com/faq/
818 http://www.webthing.com/tutorials/cgifaq.html
821 http://www.w3.org/pub/WWW/Protocols/HTTP/
824 http://www.w3.org/TR/REC-html40/
825 http://www.w3.org/pub/WWW/MarkUp/
828 http://www.w3.org/CGI/
831 http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt
833 =head2 Where can I learn about object-oriented Perl programming?
835 A good place to start is L<perltoot>, and you can use L<perlobj>,
836 L<perlboot>, and L<perlbot> for reference. Perltoot didn't come out
837 until the 5.004 release; you can get a copy (in pod, html, or
838 postscript) from http://www.perl.com/CPAN/doc/FMTEYEWTK/ .
840 =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp]
842 If you want to call C from Perl, start with L<perlxstut>,
843 moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to
844 call Perl from C, then read L<perlembed>, L<perlcall>, and
845 L<perlguts>. Don't forget that you can learn a lot from looking at
846 how the authors of existing extension modules wrote their code and
847 solved their problems.
849 =head2 I've read perlembed, perlguts, etc., but I can't embed perl in
850 my C program; what am I doing wrong?
852 Download the ExtUtils::Embed kit from CPAN and run `make test'. If
853 the tests pass, read the pods again and again and again. If they
854 fail, see L<perlbug> and send a bug report with the output of
855 C<make test TEST_VERBOSE=1> along with C<perl -V>.
857 =head2 When I tried to run my script, I got this message. What does it
860 A complete list of Perl's error messages and warnings with explanatory
861 text can be found in L<perldiag>. You can also use the splain program
862 (distributed with Perl) to explain the error messages:
864 perl program 2>diag.out
865 splain [-v] [-p] diag.out
867 or change your program to explain the messages for you:
873 use diagnostics -verbose;
875 =head2 What's MakeMaker?
877 This module (part of the standard Perl distribution) is designed to
878 write a Makefile for an extension module from a Makefile.PL. For more
879 information, see L<ExtUtils::MakeMaker>.
881 =head1 AUTHOR AND COPYRIGHT
883 Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington.
886 This documentation is free; you can redistribute it and/or modify it
887 under the same terms as Perl itself.
889 Irrespective of its distribution, all code examples here are in the public
890 domain. You are permitted and encouraged to use this code and any
891 derivatives thereof in your own programs for fun or for profit as you
892 see fit. A simple comment in the code giving credit to the FAQ would
893 be courteous but is not required.