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  1=head1 NAME
  2
  3perlfaq3 - Programming Tools ($Revision: 1.38 $, $Date: 1999/05/23 16:08:30 $)
  4
  5=head1 DESCRIPTION
  6
  7This section of the FAQ answers questions related to programmer tools
  8and programming support.
  9
 10=head2 How do I do (anything)?
 11
 12Have you looked at CPAN (see L<perlfaq2>)?  The chances are that
 13someone has already written a module that can solve your problem.
 14Have you read the appropriate man pages?  Here's a brief index:
 15
 16	Basics	        perldata, perlvar, perlsyn, perlop, perlsub
 17	Execution	perlrun, perldebug
 18	Functions	perlfunc
 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)
 27
 28A crude table of contents for the Perl man page set is found in L<perltoc>.
 29
 30=head2 How can I use Perl interactively?
 31
 32The typical approach uses the Perl debugger, described in the
 33perldebug(1) man page, on an ``empty'' program, like this:
 34
 35    perl -de 42
 36
 37Now just type in any legal Perl code, and it will be immediately
 38evaluated.  You can also examine the symbol table, get stack
 39backtraces, check variable values, set breakpoints, and other
 40operations typically found in symbolic debuggers.
 41
 42=head2 Is there a Perl shell?
 43
 44In general, no.  The Shell.pm module (distributed with Perl) makes
 45Perl try commands which aren't part of the Perl language as shell
 46commands.  perlsh from the source distribution is simplistic and
 47uninteresting, but may still be what you want.
 48
 49=head2 How do I debug my Perl programs?
 50
 51Have you tried C<use warnings> or used C<-w>?  They enable warnings 
 52to detect dubious practices.
 53
 54Have you tried C<use strict>?  It prevents you from using symbolic
 55references, makes you predeclare any subroutines that you call as bare
 56words, and (probably most importantly) forces you to predeclare your
 57variables with C<my>, C<our>, or C<use vars>.
 58
 59Did you check the return values of each and every system call?  The operating
 60system (and thus Perl) tells you whether they worked, and if not
 61why.
 62
 63  open(FH, "> /etc/cantwrite")
 64    or die "Couldn't write to /etc/cantwrite: $!\n";
 65
 66Did you read L<perltrap>?  It's full of gotchas for old and new Perl
 67programmers and even has sections for those of you who are upgrading
 68from languages like I<awk> and I<C>.
 69
 70Have you tried the Perl debugger, described in L<perldebug>?  You can
 71step through your program and see what it's doing and thus work out
 72why what it's doing isn't what it should be doing.
 73
 74=head2 How do I profile my Perl programs?
 75
 76You should get the Devel::DProf module from the standard distribution
 77(or separately on CPAN) and also use Benchmark.pm from the standard 
 78distribution.  The Benchmark module lets you time specific portions of 
 79your code, while Devel::DProf gives detailed breakdowns of where your 
 80code spends its time.
 81
 82Here's a sample use of Benchmark:
 83
 84  use Benchmark;
 85
 86  @junk = `cat /etc/motd`;
 87  $count = 10_000;
 88
 89  timethese($count, {
 90            'map' => sub { my @a = @junk;
 91			   map { s/a/b/ } @a;
 92			   return @a
 93			 },
 94            'for' => sub { my @a = @junk;
 95			   local $_;
 96			   for (@a) { s/a/b/ };
 97			   return @a },
 98           });
 99
100This is what it prints (on one machine--your results will be dependent
101on your hardware, operating system, and the load on your machine):
102
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)
106
107Be aware that a good benchmark is very hard to write.  It only tests the
108data you give it and proves little about the differing complexities
109of contrasting algorithms.
110
111=head2 How do I cross-reference my Perl programs?
112
113The 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
115to generate cross-reference reports for Perl programs.
116
117    perl -MO=Xref[,OPTIONS] scriptname.plx
118
119=head2 Is there a pretty-printer (formatter) for Perl?
120
121There is no program that will reformat Perl as much as indent(1) does
122for C.  The complex feedback between the scanner and the parser (this
123feedback is what confuses the vgrind and emacs programs) makes it
124challenging at best to write a stand-alone Perl parser.
125
126Of course, if you simply follow the guidelines in L<perlstyle>, you
127shouldn't need to reformat.  The habit of formatting your code as you
128write it will help prevent bugs.  Your editor can and should help you
129with this.  The perl-mode or newer cperl-mode for emacs can provide
130remarkable amounts of help with most (but not all) code, and even less
131programmable editors can provide significant assistance.  Tom swears
132by the following settings in vi and its clones:
133
134    set ai sw=4
135    map! ^O {^M}^[O^T
136
137Now put that in your F<.exrc> file (replacing the caret characters
138with control characters) and away you go.  In insert mode, ^T is
139for indenting, ^D is for undenting, and ^O is for blockdenting--
140as it were.  If you haven't used the last one, you're missing
141a lot.  A more complete example, with comments, can be found at
142http://www.perl.com/CPAN-local/authors/id/TOMC/scripts/toms.exrc.gz
143
144If you are used to using the I<vgrind> program for printing out nice code
145to a laser printer, you can take a stab at this using
146http://www.perl.com/CPAN/doc/misc/tips/working.vgrind.entry, but the
147results are not particularly satisfying for sophisticated code.
148
149The a2ps at http://www.infres.enst.fr/%7Edemaille/a2ps/ does lots of things
150related to generating nicely printed output of documents.
151
152=head2 Is there a ctags for Perl?
153
154There's a simple one at
155http://www.perl.com/CPAN/authors/id/TOMC/scripts/ptags.gz which may do
156the trick.  And if not, it's easy to hack into what you want.
157
158=head2 Is there an IDE or Windows Perl Editor?
159
160Perl programs are just plain text, so any editor will do.
161
162If you're on Unix, you already have an IDE--Unix itself.  The UNIX
163philosophy is the philosophy of several small tools that each do one
164thing and do it well.  It's like a carpenter's toolbox.
165
166If you want a Windows IDE, check the following:
167
168=over 4
169
170=item CodeMagicCD
171
172http://www.codemagiccd.com/
173
174=item Komodo
175
176ActiveState's cross-platform, multi-language IDE has Perl support,
177including a regular expression debugger and remote debugging
178(http://www.ActiveState.com/Products/Komodo/index.html).
179(Visual Perl, a Visual Studio.NET plug-in is currently (early 2001)
180in beta (http://www.ActiveState.com/Products/VisualPerl/index.html)).
181
182=item The Object System
183
184(http://www.castlelink.co.uk/object_system/) is a Perl web
185applications development IDE.
186
187=item PerlBuilder
188
189(http://www.solutionsoft.com/perl.htm) is an integrated development
190environment for Windows that supports Perl development.
191
192=item Perl code magic
193
194(http://www.petes-place.com/codemagic.html).
195
196=item visiPerl+
197
198http://helpconsulting.net/visiperl/, from Help Consulting.
199
200=back
201
202For editors: if you're on Unix you probably have vi or a vi clone already,
203and possibly an emacs too, so you may not need to download anything.
204In any emacs the cperl-mode (M-x cperl-mode) gives you perhaps the
205best available Perl editing mode in any editor.
206
207For Windows editors: you can download an Emacs
208
209=over 4
210
211=item GNU Emacs
212
213http://www.gnu.org/software/emacs/windows/ntemacs.html
214
215=item MicroEMACS
216
217http://members.nbci.com/uemacs/
218
219=item XEmacs
220
221http://www.xemacs.org/Download/index.html
222
223=back
224
225or a vi clone such as
226
227=over 4
228
229=item Elvis
230
231ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/
232
233=item Vile
234
235http://vile.cx/
236
237=item Vim
238
239http://www.vim.org/
240
241win32: http://www.cs.vu.nl/%7Etmgil/vi.html
242
243=back
244
245For vi lovers in general, Windows or elsewhere:
246http://www.thomer.com/thomer/vi/vi.html.
247
248nvi (http://www.bostic.com/vi/, available from CPAN in src/misc/) is
249yet another vi clone, unfortunately not available for Windows, but in
250UNIX platforms you might be interested in trying it out, firstly because
251strictly speaking it is not a vi clone, it is the real vi, or the new
252incarnation of it, and secondly because you can embed Perl inside it
253to use Perl as the scripting language.  nvi is not alone in this,
254though: at least also vim and vile offer an embedded Perl.
255
256The following are Win32 multilanguage editor/IDESs that support Perl:
257
258=over 4
259
260=item Codewright
261
262http://www.starbase.com/
263
264=item MultiEdit
265
266http://www.MultiEdit.com/
267
268=item SlickEdit
269
270http://www.slickedit.com/
271
272=back
273
274There is also a toyedit Text widget based editor written in Perl
275that is distributed with the Tk module on CPAN.  The ptkdb
276(http://world.std.com/~aep/ptkdb/) is a Perl/tk based debugger that
277acts as a development environment of sorts.  Perl Composer
278(http://perlcomposer.sourceforge.net/vperl.html) is an IDE for Perl/Tk
279GUI creation.
280
281In addition to an editor/IDE you might be interested in a more
282powerful shell environment for Win32.  Your options include
283
284=over 4
285
286=item Bash
287
288from the Cygwin package (http://sources.redhat.com/cygwin/)
289
290=item Ksh
291
292from the MKS Toolkit (http://www.mks.com/), or the Bourne shell of
293the U/WIN environment (http://www.research.att.com/sw/tools/uwin/)
294
295=item Tcsh
296
297ftp://ftp.astron.com/pub/tcsh/, see also
298http://www.primate.wisc.edu/software/csh-tcsh-book/
299
300=item Zsh
301
302ftp://ftp.blarg.net/users/amol/zsh/, see also http://www.zsh.org/
303
304=back
305
306MKS and U/WIN are commercial (U/WIN is free for educational and
307research purposes), Cygwin is covered by the GNU Public License (but
308that shouldn't matter for Perl use).  The Cygwin, MKS, and U/WIN all
309contain (in addition to the shells) a comprehensive set of standard
310UNIX toolkit utilities.
311
312If you're transferring text files between Unix and Windows using FTP
313be sure to transfer them in ASCII mode so the ends of lines are
314appropriately converted.
315
316On Mac OS the MacPerl Application comes with a simple 32k text editor
317that behaves like a rudimentary IDE.  In contrast to the MacPerl Application
318the MPW Perl tool can make use of the MPW Shell itself as an editor (with
319no 32k limit).
320
321=over 4
322
323=item BBEdit and BBEdit Lite
324
325are text editors for Mac OS that have a Perl sensitivity mode
326(http://web.barebones.com/).
327
328=item Alpha
329
330is an editor, written and extensible in Tcl, that nonetheless has
331built in support for several popular markup and programming languages
332including Perl and HTML (http://alpha.olm.net/).
333
334=back
335
336Pepper and Pe are programming language sensitive text editors for Mac
337OS X and BeOS respectively (http://www.hekkelman.com/).
338
339=head2 Where can I get Perl macros for vi?
340
341For a complete version of Tom Christiansen's vi configuration file,
342see http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc.gz ,
343the standard benchmark file for vi emulators.  The file runs best with nvi,
344the current version of vi out of Berkeley, which incidentally can be built
345with an embedded Perl interpreter--see http://www.perl.com/CPAN/src/misc.
346
347=head2 Where can I get perl-mode for emacs?
348
349Since Emacs version 19 patchlevel 22 or so, there have been both a
350perl-mode.el and support for the Perl debugger built in.  These should
351come with the standard Emacs 19 distribution.
352
353In the Perl source directory, you'll find a directory called "emacs",
354which contains a cperl-mode that color-codes keywords, provides
355context-sensitive help, and other nifty things.
356
357Note that the perl-mode of emacs will have fits with C<"main'foo">
358(single quote), and mess up the indentation and highlighting.  You
359are probably using C<"main::foo"> in new Perl code anyway, so this
360shouldn't be an issue.
361
362=head2 How can I use curses with Perl?
363
364The Curses module from CPAN provides a dynamically loadable object
365module interface to a curses library.  A small demo can be found at the
366directory http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep;
367this program repeats a command and updates the screen as needed, rendering
368B<rep ps axu> similar to B<top>.
369
370=head2 How can I use X or Tk with Perl?
371
372Tk is a completely Perl-based, object-oriented interface to the Tk toolkit
373that doesn't force you to use Tcl just to get at Tk.  Sx is an interface
374to the Athena Widget set.  Both are available from CPAN.  See the
375directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/
376
377Invaluable for Perl/Tk programming are the Perl/Tk FAQ at
378http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference
379Guide available at
380http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ , and the
381online manpages at
382http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html .
383
384=head2 How can I generate simple menus without using CGI or Tk?
385
386The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
387module, which is curses-based, can help with this.
388
389=head2 What is undump?
390
391See the next question on ``How can I make my Perl program run faster?''
392
393=head2 How can I make my Perl program run faster?
394
395The best way to do this is to come up with a better algorithm.  This
396can often make a dramatic difference.  Jon Bentley's book
397``Programming Pearls'' (that's not a misspelling!)  has some good tips
398on optimization, too.  Advice on benchmarking boils down to: benchmark
399and profile to make sure you're optimizing the right part, look for
400better algorithms instead of microtuning your code, and when all else
401fails consider just buying faster hardware.
402
403A different approach is to autoload seldom-used Perl code.  See the
404AutoSplit and AutoLoader modules in the standard distribution for
405that.  Or you could locate the bottleneck and think about writing just
406that part in C, the way we used to take bottlenecks in C code and
407write them in assembler.  Similar to rewriting in C,
408modules that have critical sections can be written in C (for instance, the
409PDL module from CPAN).
410
411In some cases, it may be worth it to use the backend compiler to
412produce byte code (saving compilation time) or compile into C, which
413will certainly save compilation time and sometimes a small amount (but
414not much) execution time.  See the question about compiling your Perl
415programs for more on the compiler--the wins aren't as obvious as you'd
416hope.
417
418If you're currently linking your perl executable to a shared I<libc.so>,
419you can often gain a 10-25% performance benefit by rebuilding it to
420link with a static libc.a instead.  This will make a bigger perl
421executable, but your Perl programs (and programmers) may thank you for
422it.  See the F<INSTALL> file in the source distribution for more
423information.
424
425Unsubstantiated reports allege that Perl interpreters that use sfio
426outperform those that don't (for I/O intensive applications).  To try
427this, see the F<INSTALL> file in the source distribution, especially
428the ``Selecting File I/O mechanisms'' section.
429
430The undump program was an old attempt to speed up your Perl program
431by storing the already-compiled form to disk.  This is no longer
432a viable option, as it only worked on a few architectures, and
433wasn't a good solution anyway.
434
435=head2 How can I make my Perl program take less memory?
436
437When it comes to time-space tradeoffs, Perl nearly always prefers to
438throw memory at a problem.  Scalars in Perl use more memory than
439strings in C, arrays take more than that, and hashes use even more.  While
440there's still a lot to be done, recent releases have been addressing
441these issues.  For example, as of 5.004, duplicate hash keys are
442shared amongst all hashes using them, so require no reallocation.
443
444In some cases, using substr() or vec() to simulate arrays can be
445highly beneficial.  For example, an array of a thousand booleans will
446take at least 20,000 bytes of space, but it can be turned into one
447125-byte bit vector--a considerable memory savings.  The standard
448Tie::SubstrHash module can also help for certain types of data
449structure.  If you're working with specialist data structures
450(matrices, for instance) modules that implement these in C may use
451less memory than equivalent Perl modules.
452
453Another thing to try is learning whether your Perl was compiled with
454the system malloc or with Perl's builtin malloc.  Whichever one it
455is, try using the other one and see whether this makes a difference.
456Information about malloc is in the F<INSTALL> file in the source
457distribution.  You can find out whether you are using perl's malloc by
458typing C<perl -V:usemymalloc>.
459
460=head2 Is it unsafe to return a pointer to local data?
461
462No, Perl's garbage collection system takes care of this.
463
464    sub makeone {
465	my @a = ( 1 .. 10 );
466	return \@a;
467    }
468
469    for $i ( 1 .. 10 ) {
470        push @many, makeone();
471    }
472
473    print $many[4][5], "\n";
474
475    print "@many\n";
476
477=head2 How can I free an array or hash so my program shrinks?
478
479You can't.  On most operating systems, memory allocated to a program
480can never be returned to the system.  That's why long-running programs
481sometimes re-exec themselves.  Some operating systems (notably,
482FreeBSD and Linux) allegedly reclaim large chunks of memory that is no
483longer used, but it doesn't appear to happen with Perl (yet).  The Mac
484appears to be the only platform that will reliably (albeit, slowly)
485return memory to the OS.
486
487We've had reports that on Linux (Redhat 5.1) on Intel, C<undef
488$scalar> will return memory to the system, while on Solaris 2.6 it
489won't.  In general, try it yourself and see.
490
491However, judicious use of my() on your variables will help make sure
492that they go out of scope so that Perl can free up that space for
493use in other parts of your program.  A global variable, of course, never
494goes out of scope, so you can't get its space automatically reclaimed,
495although undef()ing and/or delete()ing it will achieve the same effect.
496In general, memory allocation and de-allocation isn't something you can
497or should be worrying about much in Perl, but even this capability
498(preallocation of data types) is in the works.
499
500=head2 How can I make my CGI script more efficient?
501
502Beyond the normal measures described to make general Perl programs
503faster or smaller, a CGI program has additional issues.  It may be run
504several times per second.  Given that each time it runs it will need
505to be re-compiled and will often allocate a megabyte or more of system
506memory, this can be a killer.  Compiling into C B<isn't going to help
507you> because the process start-up overhead is where the bottleneck is.
508
509There are two popular ways to avoid this overhead.  One solution
510involves running the Apache HTTP server (available from
511http://www.apache.org/) with either of the mod_perl or mod_fastcgi
512plugin modules.
513
514With mod_perl and the Apache::Registry module (distributed with
515mod_perl), httpd will run with an embedded Perl interpreter which
516pre-compiles your script and then executes it within the same address
517space without forking.  The Apache extension also gives Perl access to
518the internal server API, so modules written in Perl can do just about
519anything a module written in C can.  For more on mod_perl, see
520http://perl.apache.org/
521
522With the FCGI module (from CPAN) and the mod_fastcgi
523module (available from http://www.fastcgi.com/) each of your Perl
524programs becomes a permanent CGI daemon process.
525
526Both of these solutions can have far-reaching effects on your system
527and on the way you write your CGI programs, so investigate them with
528care.
529
530See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
531
532A non-free, commercial product, ``The Velocity Engine for Perl'',
533(http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ )
534might also be worth looking at.  It will allow you to increase the
535performance of your Perl programs, running programs up to 25 times
536faster than normal CGI Perl when running in persistent Perl mode or 4
537to 5 times faster without any modification to your existing CGI
538programs. Fully functional evaluation copies are available from the
539web site.
540
541=head2 How can I hide the source for my Perl program?
542
543Delete it. :-) Seriously, there are a number of (mostly
544unsatisfactory) solutions with varying levels of ``security''.
545
546First of all, however, you I<can't> take away read permission, because
547the source code has to be readable in order to be compiled and
548interpreted.  (That doesn't mean that a CGI script's source is
549readable by people on the web, though--only by people with access to
550the filesystem.)  So you have to leave the permissions at the socially
551friendly 0755 level.
552
553Some people regard this as a security problem.  If your program does
554insecure things and relies on people not knowing how to exploit those
555insecurities, it is not secure.  It is often possible for someone to
556determine the insecure things and exploit them without viewing the
557source.  Security through obscurity, the name for hiding your bugs
558instead of fixing them, is little security indeed.
559
560You can try using encryption via source filters (Filter::* from CPAN),
561but any decent programmer will be able to decrypt it.  You can try using
562the byte code compiler and interpreter described below, but the curious
563might still be able to de-compile it.  You can try using the native-code
564compiler described below, but crackers might be able to disassemble it.
565These pose varying degrees of difficulty to people wanting to get at
566your code, but none can definitively conceal it (true of every
567language, not just Perl).
568
569If you're concerned about people profiting from your code, then the
570bottom line is that nothing but a restrictive license will give you
571legal security.  License your software and pepper it with threatening
572statements like ``This is unpublished proprietary software of XYZ Corp.
573Your access to it does not give you permission to use it blah blah
574blah.''  We are not lawyers, of course, so you should see a lawyer if
575you want to be sure your license's wording will stand up in court.
576
577=head2 How can I compile my Perl program into byte code or C?
578
579Malcolm Beattie has written a multifunction backend compiler,
580available from CPAN, that can do both these things.  It is included
581in the perl5.005 release, but is still considered experimental.
582This means it's fun to play with if you're a programmer but not
583really for people looking for turn-key solutions.
584
585Merely compiling into C does not in and of itself guarantee that your
586code will run very much faster.  That's because except for lucky cases
587where a lot of native type inferencing is possible, the normal Perl
588run-time system is still present and so your program will take just as
589long to run and be just as big.  Most programs save little more than
590compilation time, leaving execution no more than 10-30% faster.  A few
591rare programs actually benefit significantly (even running several times
592faster), but this takes some tweaking of your code.
593
594You'll probably be astonished to learn that the current version of the
595compiler generates a compiled form of your script whose executable is
596just as big as the original perl executable, and then some.  That's
597because as currently written, all programs are prepared for a full
598eval() statement.  You can tremendously reduce this cost by building a
599shared I<libperl.so> library and linking against that.  See the
600F<INSTALL> podfile in the Perl source distribution for details.  If
601you link your main perl binary with this, it will make it minuscule.
602For example, on one author's system, F</usr/bin/perl> is only 11k in
603size!
604
605In general, the compiler will do nothing to make a Perl program smaller,
606faster, more portable, or more secure.  In fact, it can make your
607situation worse.  The executable will be bigger, your VM system may take
608longer to load the whole thing, the binary is fragile and hard to fix,
609and compilation never stopped software piracy in the form of crackers,
610viruses, or bootleggers.  The real advantage of the compiler is merely
611packaging, and once you see the size of what it makes (well, unless
612you use a shared I<libperl.so>), you'll probably want a complete
613Perl install anyway.
614
615=head2 How can I compile Perl into Java?
616
617You can also integrate Java and Perl with the
618Perl Resource Kit from O'Reilly and Associates.  See
619http://www.oreilly.com/catalog/prkunix/ .
620
621Perl 5.6 comes with Java Perl Lingo, or JPL.  JPL, still in
622development, allows Perl code to be called from Java.  See jpl/README
623in the Perl source tree.
624
625=head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
626
627For OS/2 just use
628
629    extproc perl -S -your_switches
630
631as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
632`extproc' handling).  For DOS one should first invent a corresponding
633batch file and codify it in C<ALTERNATIVE_SHEBANG> (see the
634F<INSTALL> file in the source distribution for more information).
635
636The Win95/NT installation, when using the ActiveState port of Perl,
637will modify the Registry to associate the C<.pl> extension with the
638perl interpreter.  If you install another port, perhaps even building
639your own Win95/NT Perl from the standard sources by using a Windows port
640of gcc (e.g., with cygwin or mingw32), then you'll have to modify
641the Registry yourself.  In addition to associating C<.pl> with the
642interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them
643run the program C<install-linux.pl> merely by typing C<install-linux>.
644
645Macintosh Perl programs will have the appropriate Creator and
646Type, so that double-clicking them will invoke the Perl application.
647
648I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
649throw the perl interpreter into your cgi-bin directory, in order to
650get your programs working for a web server.  This is an EXTREMELY big
651security risk.  Take the time to figure out how to do it correctly.
652
653=head2 Can I write useful Perl programs on the command line?
654
655Yes.  Read L<perlrun> for more information.  Some examples follow.
656(These assume standard Unix shell quoting rules.)
657
658    # sum first and last fields
659    perl -lane 'print $F[0] + $F[-1]' *
660
661    # identify text files
662    perl -le 'for(@ARGV) {print if -f && -T _}' *
663
664    # remove (most) comments from C program
665    perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
666
667    # make file a month younger than today, defeating reaper daemons
668    perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
669
670    # find first unused uid
671    perl -le '$i++ while getpwuid($i); print $i'
672
673    # display reasonable manpath
674    echo $PATH | perl -nl -072 -e '
675	s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
676
677OK, the last one was actually an Obfuscated Perl Contest entry. :-)
678
679=head2 Why don't Perl one-liners work on my DOS/Mac/VMS system?
680
681The problem is usually that the command interpreters on those systems
682have rather different ideas about quoting than the Unix shells under
683which the one-liners were created.  On some systems, you may have to
684change single-quotes to double ones, which you must I<NOT> do on Unix
685or Plan9 systems.  You might also have to change a single % to a %%.
686
687For example:
688
689    # Unix
690    perl -e 'print "Hello world\n"'
691
692    # DOS, etc.
693    perl -e "print \"Hello world\n\""
694
695    # Mac
696    print "Hello world\n"
697     (then Run "Myscript" or Shift-Command-R)
698
699    # VMS
700    perl -e "print ""Hello world\n"""
701
702The problem is that none of these examples are reliable: they depend on the
703command interpreter.  Under Unix, the first two often work. Under DOS,
704it's entirely possible that neither works.  If 4DOS was the command shell,
705you'd probably have better luck like this:
706
707  perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
708
709Under the Mac, it depends which environment you are using.  The MacPerl
710shell, or MPW, is much like Unix shells in its support for several
711quoting variants, except that it makes free use of the Mac's non-ASCII
712characters as control characters.
713
714Using qq(), q(), and qx(), instead of "double quotes", 'single
715quotes', and `backticks`, may make one-liners easier to write.
716
717There is no general solution to all of this.  It is a mess, pure and
718simple.  Sucks to be away from Unix, huh? :-)
719
720[Some of this answer was contributed by Kenneth Albanowski.]
721
722=head2 Where can I learn about CGI or Web programming in Perl?
723
724For modules, get the CGI or LWP modules from CPAN.  For textbooks,
725see the two especially dedicated to web stuff in the question on
726books.  For problems and questions related to the web, like ``Why
727do I get 500 Errors'' or ``Why doesn't it run from the browser right
728when it runs fine on the command line'', see these sources:
729
730    WWW Security FAQ
731        http://www.w3.org/Security/Faq/
732
733    Web FAQ
734        http://www.boutell.com/faq/
735
736    CGI FAQ
737        http://www.webthing.com/tutorials/cgifaq.html
738
739    HTTP Spec
740        http://www.w3.org/pub/WWW/Protocols/HTTP/
741
742    HTML Spec
743        http://www.w3.org/TR/REC-html40/
744        http://www.w3.org/pub/WWW/MarkUp/
745
746    CGI Spec
747        http://www.w3.org/CGI/
748
749    CGI Security FAQ
750        http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt
751
752=head2 Where can I learn about object-oriented Perl programming?
753
754A good place to start is L<perltoot>, and you can use L<perlobj>,
755L<perlboot>, and L<perlbot> for reference.  Perltoot didn't come out
756until the 5.004 release; you can get a copy (in pod, html, or
757postscript) from http://www.perl.com/CPAN/doc/FMTEYEWTK/ .
758
759=head2 Where can I learn about linking C with Perl? [h2xs, xsubpp]
760
761If you want to call C from Perl, start with L<perlxstut>,
762moving on to L<perlxs>, L<xsubpp>, and L<perlguts>.  If you want to
763call Perl from C, then read L<perlembed>, L<perlcall>, and
764L<perlguts>.  Don't forget that you can learn a lot from looking at
765how the authors of existing extension modules wrote their code and
766solved their problems.
767
768=head2 I've read perlembed, perlguts, etc., but I can't embed perl in
769my C program; what am I doing wrong?
770
771Download the ExtUtils::Embed kit from CPAN and run `make test'.  If
772the tests pass, read the pods again and again and again.  If they
773fail, see L<perlbug> and send a bug report with the output of
774C<make test TEST_VERBOSE=1> along with C<perl -V>.
775
776=head2 When I tried to run my script, I got this message. What does it
777mean?
778
779A complete list of Perl's error messages and warnings with explanatory
780text can be found in L<perldiag>. You can also use the splain program
781(distributed with Perl) to explain the error messages:
782
783    perl program 2>diag.out
784    splain [-v] [-p] diag.out
785
786or change your program to explain the messages for you:
787
788    use diagnostics;
789
790or
791
792    use diagnostics -verbose;
793
794=head2 What's MakeMaker?
795
796This module (part of the standard Perl distribution) is designed to
797write a Makefile for an extension module from a Makefile.PL.  For more
798information, see L<ExtUtils::MakeMaker>.
799
800=head1 AUTHOR AND COPYRIGHT
801
802Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington.
803All rights reserved.
804
805When included as an integrated part of the Standard Distribution
806of Perl or of its documentation (printed or otherwise), this works is
807covered under Perl's Artistic License.  For separate distributions of
808all or part of this FAQ outside of that, see L<perlfaq>.
809
810Irrespective of its distribution, all code examples here are in the public
811domain.  You are permitted and encouraged to use this code and any
812derivatives thereof in your own programs for fun or for profit as you
813see fit.  A simple comment in the code giving credit to the FAQ would
814be courteous but is not required.