3 perlfaq3 - Programming Tools ($Revision: 1.33 $, $Date: 1998/12/29 20:12:12 $)
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 Regexps 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 L<perltoc> provides a crude table of contents for the perl man page set.
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 used C<-w>? It enables warnings for dubious practices.
53 Have you tried C<use strict>? It prevents you from using symbolic
54 references, makes you predeclare any subroutines that you call as bare
55 words, and (probably most importantly) forces you to predeclare your
56 variables with C<my> or C<use vars>.
58 Did you check the returns of each and every system call? The operating
59 system (and thus Perl) tells you whether they worked or not, and if not
62 open(FH, "> /etc/cantwrite")
63 or die "Couldn't write to /etc/cantwrite: $!\n";
65 Did you read L<perltrap>? It's full of gotchas for old and new Perl
66 programmers, and even has sections for those of you who are upgrading
67 from languages like I<awk> and I<C>.
69 Have you tried the Perl debugger, described in L<perldebug>? You can
70 step through your program and see what it's doing and thus work out
71 why what it's doing isn't what it should be doing.
73 =head2 How do I profile my Perl programs?
75 You should get the Devel::DProf module from CPAN, and also use
76 Benchmark.pm from the standard distribution. Benchmark lets you time
77 specific portions of your code, while Devel::DProf gives detailed
78 breakdowns of where your code spends its time.
80 Here's a sample use of Benchmark:
84 @junk = `cat /etc/motd`;
88 'map' => sub { my @a = @junk;
92 'for' => sub { my @a = @junk;
98 This is what it prints (on one machine--your results will be dependent
99 on your hardware, operating system, and the load on your machine):
101 Benchmark: timing 10000 iterations of for, map...
102 for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu)
103 map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu)
105 Be aware that a good benchmark is very hard to write. It only tests the
106 data you give it, and really proves little about differing complexities
107 of contrasting algorithms.
109 =head2 How do I cross-reference my Perl programs?
111 The B::Xref module, shipped with the new, alpha-release Perl compiler
112 (not the general distribution prior to the 5.005 release), can be used
113 to generate cross-reference reports for Perl programs.
115 perl -MO=Xref[,OPTIONS] scriptname.plx
117 =head2 Is there a pretty-printer (formatter) for Perl?
119 There is no program that will reformat Perl as much as indent(1) does
120 for C. The complex feedback between the scanner and the parser (this
121 feedback is what confuses the vgrind and emacs programs) makes it
122 challenging at best to write a stand-alone Perl parser.
124 Of course, if you simply follow the guidelines in L<perlstyle>, you
125 shouldn't need to reformat. The habit of formatting your code as you
126 write it will help prevent bugs. Your editor can and should help you
127 with this. The perl-mode for emacs can provide a remarkable amount of
128 help with most (but not all) code, and even less programmable editors
129 can provide significant assistance. Tom swears by the following
130 settings in vi and its clones:
135 Now put that in your F<.exrc> file (replacing the caret characters
136 with control characters) and away you go. In insert mode, ^T is
137 for indenting, ^D is for undenting, and ^O is for blockdenting --
138 as it were. If you haven't used the last one, you're missing
139 a lot. A more complete example, with comments, can be found at
140 http://www.perl.com/CPAN-local/authors/id/TOMC/scripts/toms.exrc.gz
142 If you are used to using the I<vgrind> program for printing out nice code
143 to a laser printer, you can take a stab at this using
144 http://www.perl.com/CPAN/doc/misc/tips/working.vgrind.entry, but the
145 results are not particularly satisfying for sophisticated code.
147 The a2ps at http://www.infres.enst.fr/~demaille/a2ps/ does lots of things
148 related to generating nicely printed output of documents.
150 =head2 Is there a ctags for Perl?
152 There's a simple one at
153 http://www.perl.com/CPAN/authors/id/TOMC/scripts/ptags.gz which may do
154 the trick. And if not, it's easy to hack into what you want.
156 =head2 Is there an IDE or Windows Perl Editor?
158 If you're on Unix, you already have an IDE -- Unix itself.
159 You just have to learn the toolbox. If you're not, then you
160 probably don't have a toolbox, so may need something else.
162 PerlBuilder (XXX URL to follow) is an integrated development
163 environment for Windows that supports Perl development. Perl programs
164 are just plain text, though, so you could download emacs for Windows
165 (XXX) or vim for win32 (http://www.cs.vu.nl/~tmgil/vi.html). If
166 you're transferring Windows files to Unix, be sure to transfer in
167 ASCII mode so the ends of lines are appropriately converted.
169 =head2 Where can I get Perl macros for vi?
171 For a complete version of Tom Christiansen's vi configuration file,
172 see http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc.gz,
173 the standard benchmark file for vi emulators. This runs best with nvi,
174 the current version of vi out of Berkeley, which incidentally can be built
175 with an embedded Perl interpreter -- see http://www.perl.com/CPAN/src/misc.
177 =head2 Where can I get perl-mode for emacs?
179 Since Emacs version 19 patchlevel 22 or so, there have been both a
180 perl-mode.el and support for the perl debugger built in. These should
181 come with the standard Emacs 19 distribution.
183 In the perl source directory, you'll find a directory called "emacs",
184 which contains a cperl-mode that color-codes keywords, provides
185 context-sensitive help, and other nifty things.
187 Note that the perl-mode of emacs will have fits with C<"main'foo">
188 (single quote), and mess up the indentation and hilighting. You
189 are probably using C<"main::foo"> in new Perl code anyway, so this
190 shouldn't be an issue.
192 =head2 How can I use curses with Perl?
194 The Curses module from CPAN provides a dynamically loadable object
195 module interface to a curses library. A small demo can be found at the
196 directory http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep;
197 this program repeats a command and updates the screen as needed, rendering
198 B<rep ps axu> similar to B<top>.
200 =head2 How can I use X or Tk with Perl?
202 Tk is a completely Perl-based, object-oriented interface to the Tk toolkit
203 that doesn't force you to use Tcl just to get at Tk. Sx is an interface
204 to the Athena Widget set. Both are available from CPAN. See the
205 directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/
207 Invaluable for Perl/Tk programming are: the Perl/Tk FAQ at
208 http://w4.lns.cornell.edu/~pvhp/ptk/ptkTOC.html , the Perl/Tk Reference
210 http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ , and the
212 http://www-users.cs.umn.edu/~amundson/perl/perltk/toc.html .
214 =head2 How can I generate simple menus without using CGI or Tk?
216 The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
217 module, which is curses-based, can help with this.
219 =head2 What is undump?
221 See the next questions.
223 =head2 How can I make my Perl program run faster?
225 The best way to do this is to come up with a better algorithm. This
226 can often make a dramatic difference. Chapter 8 in the Camel has some
227 efficiency tips in it you might want to look at. Jon Bentley's book
228 ``Programming Pearls'' (that's not a misspelling!) has some good tips
229 on optimization, too. Advice on benchmarking boils down to: benchmark
230 and profile to make sure you're optimizing the right part, look for
231 better algorithms instead of microtuning your code, and when all else
232 fails consider just buying faster hardware.
234 A different approach is to autoload seldom-used Perl code. See the
235 AutoSplit and AutoLoader modules in the standard distribution for
236 that. Or you could locate the bottleneck and think about writing just
237 that part in C, the way we used to take bottlenecks in C code and
238 write them in assembler. Similar to rewriting in C is the use of
239 modules that have critical sections written in C (for instance, the
240 PDL module from CPAN).
242 In some cases, it may be worth it to use the backend compiler to
243 produce byte code (saving compilation time) or compile into C, which
244 will certainly save compilation time and sometimes a small amount (but
245 not much) execution time. See the question about compiling your Perl
246 programs for more on the compiler--the wins aren't as obvious as you'd
249 If you're currently linking your perl executable to a shared I<libc.so>,
250 you can often gain a 10-25% performance benefit by rebuilding it to
251 link with a static libc.a instead. This will make a bigger perl
252 executable, but your Perl programs (and programmers) may thank you for
253 it. See the F<INSTALL> file in the source distribution for more
256 Unsubstantiated reports allege that Perl interpreters that use sfio
257 outperform those that don't (for IO intensive applications). To try
258 this, see the F<INSTALL> file in the source distribution, especially
259 the ``Selecting File IO mechanisms'' section.
261 The undump program was an old attempt to speed up your Perl program
262 by storing the already-compiled form to disk. This is no longer
263 a viable option, as it only worked on a few architectures, and
264 wasn't a good solution anyway.
266 =head2 How can I make my Perl program take less memory?
268 When it comes to time-space tradeoffs, Perl nearly always prefers to
269 throw memory at a problem. Scalars in Perl use more memory than
270 strings in C, arrays take more than that, and hashes use even more. While
271 there's still a lot to be done, recent releases have been addressing
272 these issues. For example, as of 5.004, duplicate hash keys are
273 shared amongst all hashes using them, so require no reallocation.
275 In some cases, using substr() or vec() to simulate arrays can be
276 highly beneficial. For example, an array of a thousand booleans will
277 take at least 20,000 bytes of space, but it can be turned into one
278 125-byte bit vector for a considerable memory savings. The standard
279 Tie::SubstrHash module can also help for certain types of data
280 structure. If you're working with specialist data structures
281 (matrices, for instance) modules that implement these in C may use
282 less memory than equivalent Perl modules.
284 Another thing to try is learning whether your Perl was compiled with
285 the system malloc or with Perl's builtin malloc. Whichever one it
286 is, try using the other one and see whether this makes a difference.
287 Information about malloc is in the F<INSTALL> file in the source
288 distribution. You can find out whether you are using perl's malloc by
289 typing C<perl -V:usemymalloc>.
291 =head2 Is it unsafe to return a pointer to local data?
293 No, Perl's garbage collection system takes care of this.
301 push @many, makeone();
304 print $many[4][5], "\n";
308 =head2 How can I free an array or hash so my program shrinks?
310 You can't. On most operating systems, memory allocated to a program
311 can never be returned to the system. That's why long-running programs
312 sometimes re-exec themselves. Some operating systems (notably,
313 FreeBSD and Linux) allegedly reclaim large chunks of memory that is no
314 longer used, but it doesn't appear to happen with Perl (yet). The Mac
315 appears to be the only platform that will reliably (albeit, slowly)
316 return memory to the OS.
318 We've had reports that on Linux (Redhat 5.1) on Intel, C<undef
319 $scalar> will return memory to the system, while on Solaris 2.6 it
320 won't. In general, try it yourself and see.
322 However, judicious use of my() on your variables will help make sure
323 that they go out of scope so that Perl can free up their storage for
324 use in other parts of your program. A global variable, of course, never
325 goes out of scope, so you can't get its space automatically reclaimed,
326 although undef()ing and/or delete()ing it will achieve the same effect.
327 In general, memory allocation and de-allocation isn't something you can
328 or should be worrying about much in Perl, but even this capability
329 (preallocation of data types) is in the works.
331 =head2 How can I make my CGI script more efficient?
333 Beyond the normal measures described to make general Perl programs
334 faster or smaller, a CGI program has additional issues. It may be run
335 several times per second. Given that each time it runs it will need
336 to be re-compiled and will often allocate a megabyte or more of system
337 memory, this can be a killer. Compiling into C B<isn't going to help
338 you> because the process start-up overhead is where the bottleneck is.
340 There are two popular ways to avoid this overhead. One solution
341 involves running the Apache HTTP server (available from
342 http://www.apache.org/) with either of the mod_perl or mod_fastcgi
345 With mod_perl and the Apache::Registry module (distributed with
346 mod_perl), httpd will run with an embedded Perl interpreter which
347 pre-compiles your script and then executes it within the same address
348 space without forking. The Apache extension also gives Perl access to
349 the internal server API, so modules written in Perl can do just about
350 anything a module written in C can. For more on mod_perl, see
351 http://perl.apache.org/
353 With the FCGI module (from CPAN) and the mod_fastcgi
354 module (available from http://www.fastcgi.com/) each of your perl
355 scripts becomes a permanent CGI daemon process.
357 Both of these solutions can have far-reaching effects on your system
358 and on the way you write your CGI scripts, so investigate them with
361 See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
363 A non-free, commercial product, ``The Velocity Engine for Perl'',
364 (http://www.binevolve.com/ or http://www.binevolve.com/bine/vep) might
365 also be worth looking at. It will allow you to increase the performance
366 of your perl scripts, upto 25 times faster than normal CGI perl by
367 running in persistent perl mode, or 4 to 5 times faster without any
368 modification to your existing CGI scripts. Fully functional evaluation
369 copies are available from the web site.
371 =head2 How can I hide the source for my Perl program?
373 Delete it. :-) Seriously, there are a number of (mostly
374 unsatisfactory) solutions with varying levels of ``security''.
376 First of all, however, you I<can't> take away read permission, because
377 the source code has to be readable in order to be compiled and
378 interpreted. (That doesn't mean that a CGI script's source is
379 readable by people on the web, though, only by people with access to
380 the filesystem) So you have to leave the permissions at the socially
383 Some people regard this as a security problem. If your program does
384 insecure things, and relies on people not knowing how to exploit those
385 insecurities, it is not secure. It is often possible for someone to
386 determine the insecure things and exploit them without viewing the
387 source. Security through obscurity, the name for hiding your bugs
388 instead of fixing them, is little security indeed.
390 You can try using encryption via source filters (Filter::* from CPAN),
391 but any decent programmer will be able to decrypt it. You can try using
392 the byte code compiler and interpreter described below, but the curious
393 might still be able to de-compile it. You can try using the native-code
394 compiler described below, but crackers might be able to disassemble it.
395 These pose varying degrees of difficulty to people wanting to get at
396 your code, but none can definitively conceal it (this is true of every
397 language, not just Perl).
399 If you're concerned about people profiting from your code, then the
400 bottom line is that nothing but a restrictive licence will give you
401 legal security. License your software and pepper it with threatening
402 statements like ``This is unpublished proprietary software of XYZ Corp.
403 Your access to it does not give you permission to use it blah blah
404 blah.'' We are not lawyers, of course, so you should see a lawyer if
405 you want to be sure your licence's wording will stand up in court.
407 =head2 How can I compile my Perl program into byte code or C?
409 Malcolm Beattie has written a multifunction backend compiler,
410 available from CPAN, that can do both these things. It is included
411 in the perl5.005 release, but is still considered experimental.
412 This means it's fun to play with if you're a programmer but not
413 really for people looking for turn-key solutions.
415 Merely compiling into C does not in and of itself guarantee that your
416 code will run very much faster. That's because except for lucky cases
417 where a lot of native type inferencing is possible, the normal Perl
418 run time system is still present and so your program will take just as
419 long to run and be just as big. Most programs save little more than
420 compilation time, leaving execution no more than 10-30% faster. A few
421 rare programs actually benefit significantly (like several times
422 faster), but this takes some tweaking of your code.
424 You'll probably be astonished to learn that the current version of the
425 compiler generates a compiled form of your script whose executable is
426 just as big as the original perl executable, and then some. That's
427 because as currently written, all programs are prepared for a full
428 eval() statement. You can tremendously reduce this cost by building a
429 shared I<libperl.so> library and linking against that. See the
430 F<INSTALL> podfile in the perl source distribution for details. If
431 you link your main perl binary with this, it will make it miniscule.
432 For example, on one author's system, F</usr/bin/perl> is only 11k in
435 In general, the compiler will do nothing to make a Perl program smaller,
436 faster, more portable, or more secure. In fact, it will usually hurt
437 all of those. The executable will be bigger, your VM system may take
438 longer to load the whole thing, the binary is fragile and hard to fix,
439 and compilation never stopped software piracy in the form of crackers,
440 viruses, or bootleggers. The real advantage of the compiler is merely
441 packaging, and once you see the size of what it makes (well, unless
442 you use a shared I<libperl.so>), you'll probably want a complete
445 =head2 How can I compile Perl into Java?
447 You can't. Not yet, anyway. You can integrate Java and Perl with the
448 Perl Resource Kit from O'Reilly and Associates. See
449 http://www.oreilly.com/catalog/prkunix/ for more information.
450 The Java interface will be supported in the core 5.006 release
453 =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
457 extproc perl -S -your_switches
459 as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
460 `extproc' handling). For DOS one should first invent a corresponding
461 batch file, and codify it in C<ALTERNATIVE_SHEBANG> (see the
462 F<INSTALL> file in the source distribution for more information).
464 The Win95/NT installation, when using the ActiveState port of Perl,
465 will modify the Registry to associate the C<.pl> extension with the
466 perl interpreter. If you install another port (Gurusamy Sarathy's is
467 the recommended Win95/NT port), or (eventually) build your own
468 Win95/NT Perl using a Windows port of gcc (e.g., with cygwin32 or
469 mingw32), then you'll have to modify the Registry yourself. In
470 addition to associating C<.pl> with the interpreter, NT people can
471 use: C<SET PATHEXT=%PATHEXT%;.PL> to let them run the program
472 C<install-linux.pl> merely by typing C<install-linux>.
474 Macintosh perl scripts will have the appropriate Creator and
475 Type, so that double-clicking them will invoke the perl application.
477 I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
478 throw the perl interpreter into your cgi-bin directory, in order to
479 get your scripts working for a web server. This is an EXTREMELY big
480 security risk. Take the time to figure out how to do it correctly.
482 =head2 Can I write useful perl programs on the command line?
484 Yes. Read L<perlrun> for more information. Some examples follow.
485 (These assume standard Unix shell quoting rules.)
487 # sum first and last fields
488 perl -lane 'print $F[0] + $F[-1]' *
490 # identify text files
491 perl -le 'for(@ARGV) {print if -f && -T _}' *
493 # remove (most) comments from C program
494 perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
496 # make file a month younger than today, defeating reaper daemons
497 perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
499 # find first unused uid
500 perl -le '$i++ while getpwuid($i); print $i'
502 # display reasonable manpath
503 echo $PATH | perl -nl -072 -e '
504 s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
506 Ok, the last one was actually an obfuscated perl entry. :-)
508 =head2 Why don't perl one-liners work on my DOS/Mac/VMS system?
510 The problem is usually that the command interpreters on those systems
511 have rather different ideas about quoting than the Unix shells under
512 which the one-liners were created. On some systems, you may have to
513 change single-quotes to double ones, which you must I<NOT> do on Unix
514 or Plan9 systems. You might also have to change a single % to a %%.
519 perl -e 'print "Hello world\n"'
522 perl -e "print \"Hello world\n\""
525 print "Hello world\n"
526 (then Run "Myscript" or Shift-Command-R)
529 perl -e "print ""Hello world\n"""
531 The problem is that none of this is reliable: it depends on the
532 command interpreter. Under Unix, the first two often work. Under DOS,
533 it's entirely possible neither works. If 4DOS was the command shell,
534 you'd probably have better luck like this:
536 perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
538 Under the Mac, it depends which environment you are using. The MacPerl
539 shell, or MPW, is much like Unix shells in its support for several
540 quoting variants, except that it makes free use of the Mac's non-ASCII
541 characters as control characters.
543 Using qq(), q(), and qx(), instead of "double quotes", 'single
544 quotes', and `backticks`, may make one-liners easier to write.
546 There is no general solution to all of this. It is a mess, pure and
547 simple. Sucks to be away from Unix, huh? :-)
549 [Some of this answer was contributed by Kenneth Albanowski.]
551 =head2 Where can I learn about CGI or Web programming in Perl?
553 For modules, get the CGI or LWP modules from CPAN. For textbooks,
554 see the two especially dedicated to web stuff in the question on
555 books. For problems and questions related to the web, like ``Why
556 do I get 500 Errors'' or ``Why doesn't it run from the browser right
557 when it runs fine on the command line'', see these sources:
560 http://www.w3.org/Security/Faq/
563 http://www.boutell.com/faq/
566 http://www.webthing.com/page.cgi/cgifaq
569 http://www.w3.org/pub/WWW/Protocols/HTTP/
572 http://www.w3.org/TR/REC-html40/
573 http://www.w3.org/pub/WWW/MarkUp/
576 http://www.w3.org/CGI/
579 http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt
582 =head2 Where can I learn about object-oriented Perl programming?
584 L<perltoot> is a good place to start, and you can use L<perlobj> and
585 L<perlbot> for reference. Perltoot didn't come out until the 5.004
586 release, but you can get a copy (in pod, html, or postscript) from
587 http://www.perl.com/CPAN/doc/FMTEYEWTK/ .
589 =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp]
591 If you want to call C from Perl, start with L<perlxstut>,
592 moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to
593 call Perl from C, then read L<perlembed>, L<perlcall>, and
594 L<perlguts>. Don't forget that you can learn a lot from looking at
595 how the authors of existing extension modules wrote their code and
596 solved their problems.
598 =head2 I've read perlembed, perlguts, etc., but I can't embed perl in
599 my C program, what am I doing wrong?
601 Download the ExtUtils::Embed kit from CPAN and run `make test'. If
602 the tests pass, read the pods again and again and again. If they
603 fail, see L<perlbug> and send a bugreport with the output of
604 C<make test TEST_VERBOSE=1> along with C<perl -V>.
606 =head2 When I tried to run my script, I got this message. What does it
609 L<perldiag> has a complete list of perl's error messages and warnings,
610 with explanatory text. You can also use the splain program (distributed
611 with perl) to explain the error messages:
613 perl program 2>diag.out
614 splain [-v] [-p] diag.out
616 or change your program to explain the messages for you:
622 use diagnostics -verbose;
624 =head2 What's MakeMaker?
626 This module (part of the standard perl distribution) is designed to
627 write a Makefile for an extension module from a Makefile.PL. For more
628 information, see L<ExtUtils::MakeMaker>.
630 =head1 AUTHOR AND COPYRIGHT
632 Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington.
635 When included as an integrated part of the Standard Distribution
636 of Perl or of its documentation (printed or otherwise), this works is
637 covered under Perl's Artistic Licence. For separate distributions of
638 all or part of this FAQ outside of that, see L<perlfaq>.
640 Irrespective of its distribution, all code examples here are public
641 domain. You are permitted and encouraged to use this code and any
642 derivatives thereof in your own programs for fun or for profit as you
643 see fit. A simple comment in the code giving credit to the FAQ would
644 be courteous but is not required.