--- /dev/null
+=head1 NAME
+
+perlfaq3 - Programming Tools ($Revision: 1.38 $, $Date: 1999/05/23 16:08:30 $)
+
+=head1 DESCRIPTION
+
+This section of the FAQ answers questions related to programmer tools
+and programming support.
+
+=head2 How do I do (anything)?
+
+Have you looked at CPAN (see L<perlfaq2>)? The chances are that
+someone has already written a module that can solve your problem.
+Have you read the appropriate man pages? Here's a brief index:
+
+ Basics perldata, perlvar, perlsyn, perlop, perlsub
+ Execution perlrun, perldebug
+ Functions perlfunc
+ Objects perlref, perlmod, perlobj, perltie
+ Data Structures perlref, perllol, perldsc
+ Modules perlmod, perlmodlib, perlsub
+ Regexes perlre, perlfunc, perlop, perllocale
+ Moving to perl5 perltrap, perl
+ Linking w/C perlxstut, perlxs, perlcall, perlguts, perlembed
+ Various http://www.perl.com/CPAN/doc/FMTEYEWTK/index.html
+ (not a man-page but still useful)
+
+A crude table of contents for the Perl man page set is found in L<perltoc>.
+
+=head2 How can I use Perl interactively?
+
+The typical approach uses the Perl debugger, described in the
+perldebug(1) man page, on an ``empty'' program, like this:
+
+ perl -de 42
+
+Now just type in any legal Perl code, and it will be immediately
+evaluated. You can also examine the symbol table, get stack
+backtraces, check variable values, set breakpoints, and other
+operations typically found in symbolic debuggers.
+
+=head2 Is there a Perl shell?
+
+In general, no. The Shell.pm module (distributed with Perl) makes
+Perl try commands which aren't part of the Perl language as shell
+commands. perlsh from the source distribution is simplistic and
+uninteresting, but may still be what you want.
+
+=head2 How do I debug my Perl programs?
+
+Have you tried C<use warnings> or used C<-w>? They enable warnings
+to detect dubious practices.
+
+Have you tried C<use strict>? It prevents you from using symbolic
+references, makes you predeclare any subroutines that you call as bare
+words, and (probably most importantly) forces you to predeclare your
+variables with C<my>, C<our>, or C<use vars>.
+
+Did you check the return values of each and every system call? The operating
+system (and thus Perl) tells you whether they worked, and if not
+why.
+
+ open(FH, "> /etc/cantwrite")
+ or die "Couldn't write to /etc/cantwrite: $!\n";
+
+Did you read L<perltrap>? It's full of gotchas for old and new Perl
+programmers and even has sections for those of you who are upgrading
+from languages like I<awk> and I<C>.
+
+Have you tried the Perl debugger, described in L<perldebug>? You can
+step through your program and see what it's doing and thus work out
+why what it's doing isn't what it should be doing.
+
+=head2 How do I profile my Perl programs?
+
+You should get the Devel::DProf module from the standard distribution
+(or separately on CPAN) and also use Benchmark.pm from the standard
+distribution. The Benchmark module lets you time specific portions of
+your code, while Devel::DProf gives detailed breakdowns of where your
+code spends its time.
+
+Here's a sample use of Benchmark:
+
+ use Benchmark;
+
+ @junk = `cat /etc/motd`;
+ $count = 10_000;
+
+ timethese($count, {
+ 'map' => sub { my @a = @junk;
+ map { s/a/b/ } @a;
+ return @a
+ },
+ 'for' => sub { my @a = @junk;
+ local $_;
+ for (@a) { s/a/b/ };
+ return @a },
+ });
+
+This is what it prints (on one machine--your results will be dependent
+on your hardware, operating system, and the load on your machine):
+
+ Benchmark: timing 10000 iterations of for, map...
+ for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu)
+ map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu)
+
+Be aware that a good benchmark is very hard to write. It only tests the
+data you give it and proves little about the differing complexities
+of contrasting algorithms.
+
+=head2 How do I cross-reference my Perl programs?
+
+The B::Xref module, shipped with the new, alpha-release Perl compiler
+(not the general distribution prior to the 5.005 release), can be used
+to generate cross-reference reports for Perl programs.
+
+ perl -MO=Xref[,OPTIONS] scriptname.plx
+
+=head2 Is there a pretty-printer (formatter) for Perl?
+
+There is no program that will reformat Perl as much as indent(1) does
+for C. The complex feedback between the scanner and the parser (this
+feedback is what confuses the vgrind and emacs programs) makes it
+challenging at best to write a stand-alone Perl parser.
+
+Of course, if you simply follow the guidelines in L<perlstyle>, you
+shouldn't need to reformat. The habit of formatting your code as you
+write it will help prevent bugs. Your editor can and should help you
+with this. The perl-mode or newer cperl-mode for emacs can provide
+remarkable amounts of help with most (but not all) code, and even less
+programmable editors can provide significant assistance. Tom swears
+by the following settings in vi and its clones:
+
+ set ai sw=4
+ map! ^O {^M}^[O^T
+
+Now put that in your F<.exrc> file (replacing the caret characters
+with control characters) and away you go. In insert mode, ^T is
+for indenting, ^D is for undenting, and ^O is for blockdenting--
+as it were. If you haven't used the last one, you're missing
+a lot. A more complete example, with comments, can be found at
+http://www.perl.com/CPAN-local/authors/id/TOMC/scripts/toms.exrc.gz
+
+If you are used to using the I<vgrind> program for printing out nice code
+to a laser printer, you can take a stab at this using
+http://www.perl.com/CPAN/doc/misc/tips/working.vgrind.entry, but the
+results are not particularly satisfying for sophisticated code.
+
+The a2ps at http://www.infres.enst.fr/%7Edemaille/a2ps/ does lots of things
+related to generating nicely printed output of documents.
+
+=head2 Is there a ctags for Perl?
+
+There's a simple one at
+http://www.perl.com/CPAN/authors/id/TOMC/scripts/ptags.gz which may do
+the trick. And if not, it's easy to hack into what you want.
+
+=head2 Is there an IDE or Windows Perl Editor?
+
+Perl programs are just plain text, so any editor will do.
+
+If you're on Unix, you already have an IDE--Unix itself. The UNIX
+philosophy is the philosophy of several small tools that each do one
+thing and do it well. It's like a carpenter's toolbox.
+
+If you want a Windows IDE, check the following:
+
+=over 4
+
+=item CodeMagicCD
+
+http://www.codemagiccd.com/
+
+=item Komodo
+
+ActiveState's cross-platform, multi-language IDE has Perl support,
+including a regular expression debugger and remote debugging
+(http://www.ActiveState.com/Products/Komodo/index.html).
+(Visual Perl, a Visual Studio.NET plug-in is currently (early 2001)
+in beta (http://www.ActiveState.com/Products/VisualPerl/index.html)).
+
+=item The Object System
+
+(http://www.castlelink.co.uk/object_system/) is a Perl web
+applications development IDE.
+
+=item PerlBuilder
+
+(http://www.solutionsoft.com/perl.htm) is an integrated development
+environment for Windows that supports Perl development.
+
+=item Perl code magic
+
+(http://www.petes-place.com/codemagic.html).
+
+=item visiPerl+
+
+http://helpconsulting.net/visiperl/, from Help Consulting.
+
+=back
+
+For editors: if you're on Unix you probably have vi or a vi clone already,
+and possibly an emacs too, so you may not need to download anything.
+In any emacs the cperl-mode (M-x cperl-mode) gives you perhaps the
+best available Perl editing mode in any editor.
+
+For Windows editors: you can download an Emacs
+
+=over 4
+
+=item GNU Emacs
+
+http://www.gnu.org/software/emacs/windows/ntemacs.html
+
+=item MicroEMACS
+
+http://members.nbci.com/uemacs/
+
+=item XEmacs
+
+http://www.xemacs.org/Download/index.html
+
+=back
+
+or a vi clone such as
+
+=over 4
+
+=item Elvis
+
+ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/
+
+=item Vile
+
+http://vile.cx/
+
+=item Vim
+
+http://www.vim.org/
+
+win32: http://www.cs.vu.nl/%7Etmgil/vi.html
+
+=back
+
+For vi lovers in general, Windows or elsewhere:
+http://www.thomer.com/thomer/vi/vi.html.
+
+nvi (http://www.bostic.com/vi/, available from CPAN in src/misc/) is
+yet another vi clone, unfortunately not available for Windows, but in
+UNIX platforms you might be interested in trying it out, firstly because
+strictly speaking it is not a vi clone, it is the real vi, or the new
+incarnation of it, and secondly because you can embed Perl inside it
+to use Perl as the scripting language. nvi is not alone in this,
+though: at least also vim and vile offer an embedded Perl.
+
+The following are Win32 multilanguage editor/IDESs that support Perl:
+
+=over 4
+
+=item Codewright
+
+http://www.starbase.com/
+
+=item MultiEdit
+
+http://www.MultiEdit.com/
+
+=item SlickEdit
+
+http://www.slickedit.com/
+
+=back
+
+There is also a toyedit Text widget based editor written in Perl
+that is distributed with the Tk module on CPAN. The ptkdb
+(http://world.std.com/~aep/ptkdb/) is a Perl/tk based debugger that
+acts as a development environment of sorts. Perl Composer
+(http://perlcomposer.sourceforge.net/vperl.html) is an IDE for Perl/Tk
+GUI creation.
+
+In addition to an editor/IDE you might be interested in a more
+powerful shell environment for Win32. Your options include
+
+=over 4
+
+=item Bash
+
+from the Cygwin package (http://sources.redhat.com/cygwin/)
+
+=item Ksh
+
+from the MKS Toolkit (http://www.mks.com/), or the Bourne shell of
+the U/WIN environment (http://www.research.att.com/sw/tools/uwin/)
+
+=item Tcsh
+
+ftp://ftp.astron.com/pub/tcsh/, see also
+http://www.primate.wisc.edu/software/csh-tcsh-book/
+
+=item Zsh
+
+ftp://ftp.blarg.net/users/amol/zsh/, see also http://www.zsh.org/
+
+=back
+
+MKS and U/WIN are commercial (U/WIN is free for educational and
+research purposes), Cygwin is covered by the GNU Public License (but
+that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all
+contain (in addition to the shells) a comprehensive set of standard
+UNIX toolkit utilities.
+
+If you're transferring text files between Unix and Windows using FTP
+be sure to transfer them in ASCII mode so the ends of lines are
+appropriately converted.
+
+On Mac OS the MacPerl Application comes with a simple 32k text editor
+that behaves like a rudimentary IDE. In contrast to the MacPerl Application
+the MPW Perl tool can make use of the MPW Shell itself as an editor (with
+no 32k limit).
+
+=over 4
+
+=item BBEdit and BBEdit Lite
+
+are text editors for Mac OS that have a Perl sensitivity mode
+(http://web.barebones.com/).
+
+=item Alpha
+
+is an editor, written and extensible in Tcl, that nonetheless has
+built in support for several popular markup and programming languages
+including Perl and HTML (http://alpha.olm.net/).
+
+=back
+
+Pepper and Pe are programming language sensitive text editors for Mac
+OS X and BeOS respectively (http://www.hekkelman.com/).
+
+=head2 Where can I get Perl macros for vi?
+
+For a complete version of Tom Christiansen's vi configuration file,
+see http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc.gz ,
+the standard benchmark file for vi emulators. The file runs best with nvi,
+the current version of vi out of Berkeley, which incidentally can be built
+with an embedded Perl interpreter--see http://www.perl.com/CPAN/src/misc.
+
+=head2 Where can I get perl-mode for emacs?
+
+Since Emacs version 19 patchlevel 22 or so, there have been both a
+perl-mode.el and support for the Perl debugger built in. These should
+come with the standard Emacs 19 distribution.
+
+In the Perl source directory, you'll find a directory called "emacs",
+which contains a cperl-mode that color-codes keywords, provides
+context-sensitive help, and other nifty things.
+
+Note that the perl-mode of emacs will have fits with C<"main'foo">
+(single quote), and mess up the indentation and highlighting. You
+are probably using C<"main::foo"> in new Perl code anyway, so this
+shouldn't be an issue.
+
+=head2 How can I use curses with Perl?
+
+The Curses module from CPAN provides a dynamically loadable object
+module interface to a curses library. A small demo can be found at the
+directory http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep;
+this program repeats a command and updates the screen as needed, rendering
+B<rep ps axu> similar to B<top>.
+
+=head2 How can I use X or Tk with Perl?
+
+Tk is a completely Perl-based, object-oriented interface to the Tk toolkit
+that doesn't force you to use Tcl just to get at Tk. Sx is an interface
+to the Athena Widget set. Both are available from CPAN. See the
+directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/
+
+Invaluable for Perl/Tk programming are the Perl/Tk FAQ at
+http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference
+Guide available at
+http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ , and the
+online manpages at
+http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html .
+
+=head2 How can I generate simple menus without using CGI or Tk?
+
+The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
+module, which is curses-based, can help with this.
+
+=head2 What is undump?
+
+See the next question on ``How can I make my Perl program run faster?''
+
+=head2 How can I make my Perl program run faster?
+
+The best way to do this is to come up with a better algorithm. This
+can often make a dramatic difference. Jon Bentley's book
+``Programming Pearls'' (that's not a misspelling!) has some good tips
+on optimization, too. Advice on benchmarking boils down to: benchmark
+and profile to make sure you're optimizing the right part, look for
+better algorithms instead of microtuning your code, and when all else
+fails consider just buying faster hardware.
+
+A different approach is to autoload seldom-used Perl code. See the
+AutoSplit and AutoLoader modules in the standard distribution for
+that. Or you could locate the bottleneck and think about writing just
+that part in C, the way we used to take bottlenecks in C code and
+write them in assembler. Similar to rewriting in C,
+modules that have critical sections can be written in C (for instance, the
+PDL module from CPAN).
+
+In some cases, it may be worth it to use the backend compiler to
+produce byte code (saving compilation time) or compile into C, which
+will certainly save compilation time and sometimes a small amount (but
+not much) execution time. See the question about compiling your Perl
+programs for more on the compiler--the wins aren't as obvious as you'd
+hope.
+
+If you're currently linking your perl executable to a shared I<libc.so>,
+you can often gain a 10-25% performance benefit by rebuilding it to
+link with a static libc.a instead. This will make a bigger perl
+executable, but your Perl programs (and programmers) may thank you for
+it. See the F<INSTALL> file in the source distribution for more
+information.
+
+Unsubstantiated reports allege that Perl interpreters that use sfio
+outperform those that don't (for I/O intensive applications). To try
+this, see the F<INSTALL> file in the source distribution, especially
+the ``Selecting File I/O mechanisms'' section.
+
+The undump program was an old attempt to speed up your Perl program
+by storing the already-compiled form to disk. This is no longer
+a viable option, as it only worked on a few architectures, and
+wasn't a good solution anyway.
+
+=head2 How can I make my Perl program take less memory?
+
+When it comes to time-space tradeoffs, Perl nearly always prefers to
+throw memory at a problem. Scalars in Perl use more memory than
+strings in C, arrays take more than that, and hashes use even more. While
+there's still a lot to be done, recent releases have been addressing
+these issues. For example, as of 5.004, duplicate hash keys are
+shared amongst all hashes using them, so require no reallocation.
+
+In some cases, using substr() or vec() to simulate arrays can be
+highly beneficial. For example, an array of a thousand booleans will
+take at least 20,000 bytes of space, but it can be turned into one
+125-byte bit vector--a considerable memory savings. The standard
+Tie::SubstrHash module can also help for certain types of data
+structure. If you're working with specialist data structures
+(matrices, for instance) modules that implement these in C may use
+less memory than equivalent Perl modules.
+
+Another thing to try is learning whether your Perl was compiled with
+the system malloc or with Perl's builtin malloc. Whichever one it
+is, try using the other one and see whether this makes a difference.
+Information about malloc is in the F<INSTALL> file in the source
+distribution. You can find out whether you are using perl's malloc by
+typing C<perl -V:usemymalloc>.
+
+=head2 Is it unsafe to return a pointer to local data?
+
+No, Perl's garbage collection system takes care of this.
+
+ sub makeone {
+ my @a = ( 1 .. 10 );
+ return \@a;
+ }
+
+ for $i ( 1 .. 10 ) {
+ push @many, makeone();
+ }
+
+ print $many[4][5], "\n";
+
+ print "@many\n";
+
+=head2 How can I free an array or hash so my program shrinks?
+
+You can't. On most operating systems, memory allocated to a program
+can never be returned to the system. That's why long-running programs
+sometimes re-exec themselves. Some operating systems (notably,
+FreeBSD and Linux) allegedly reclaim large chunks of memory that is no
+longer used, but it doesn't appear to happen with Perl (yet). The Mac
+appears to be the only platform that will reliably (albeit, slowly)
+return memory to the OS.
+
+We've had reports that on Linux (Redhat 5.1) on Intel, C<undef
+$scalar> will return memory to the system, while on Solaris 2.6 it
+won't. In general, try it yourself and see.
+
+However, judicious use of my() on your variables will help make sure
+that they go out of scope so that Perl can free up that space for
+use in other parts of your program. A global variable, of course, never
+goes out of scope, so you can't get its space automatically reclaimed,
+although undef()ing and/or delete()ing it will achieve the same effect.
+In general, memory allocation and de-allocation isn't something you can
+or should be worrying about much in Perl, but even this capability
+(preallocation of data types) is in the works.
+
+=head2 How can I make my CGI script more efficient?
+
+Beyond the normal measures described to make general Perl programs
+faster or smaller, a CGI program has additional issues. It may be run
+several times per second. Given that each time it runs it will need
+to be re-compiled and will often allocate a megabyte or more of system
+memory, this can be a killer. Compiling into C B<isn't going to help
+you> because the process start-up overhead is where the bottleneck is.
+
+There are two popular ways to avoid this overhead. One solution
+involves running the Apache HTTP server (available from
+http://www.apache.org/) with either of the mod_perl or mod_fastcgi
+plugin modules.
+
+With mod_perl and the Apache::Registry module (distributed with
+mod_perl), httpd will run with an embedded Perl interpreter which
+pre-compiles your script and then executes it within the same address
+space without forking. The Apache extension also gives Perl access to
+the internal server API, so modules written in Perl can do just about
+anything a module written in C can. For more on mod_perl, see
+http://perl.apache.org/
+
+With the FCGI module (from CPAN) and the mod_fastcgi
+module (available from http://www.fastcgi.com/) each of your Perl
+programs becomes a permanent CGI daemon process.
+
+Both of these solutions can have far-reaching effects on your system
+and on the way you write your CGI programs, so investigate them with
+care.
+
+See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
+
+A non-free, commercial product, ``The Velocity Engine for Perl'',
+(http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ )
+might also be worth looking at. It will allow you to increase the
+performance of your Perl programs, running programs up to 25 times
+faster than normal CGI Perl when running in persistent Perl mode or 4
+to 5 times faster without any modification to your existing CGI
+programs. Fully functional evaluation copies are available from the
+web site.
+
+=head2 How can I hide the source for my Perl program?
+
+Delete it. :-) Seriously, there are a number of (mostly
+unsatisfactory) solutions with varying levels of ``security''.
+
+First of all, however, you I<can't> take away read permission, because
+the source code has to be readable in order to be compiled and
+interpreted. (That doesn't mean that a CGI script's source is
+readable by people on the web, though--only by people with access to
+the filesystem.) So you have to leave the permissions at the socially
+friendly 0755 level.
+
+Some people regard this as a security problem. If your program does
+insecure things and relies on people not knowing how to exploit those
+insecurities, it is not secure. It is often possible for someone to
+determine the insecure things and exploit them without viewing the
+source. Security through obscurity, the name for hiding your bugs
+instead of fixing them, is little security indeed.
+
+You can try using encryption via source filters (Filter::* from CPAN),
+but any decent programmer will be able to decrypt it. You can try using
+the byte code compiler and interpreter described below, but the curious
+might still be able to de-compile it. You can try using the native-code
+compiler described below, but crackers might be able to disassemble it.
+These pose varying degrees of difficulty to people wanting to get at
+your code, but none can definitively conceal it (true of every
+language, not just Perl).
+
+If you're concerned about people profiting from your code, then the
+bottom line is that nothing but a restrictive license will give you
+legal security. License your software and pepper it with threatening
+statements like ``This is unpublished proprietary software of XYZ Corp.
+Your access to it does not give you permission to use it blah blah
+blah.'' We are not lawyers, of course, so you should see a lawyer if
+you want to be sure your license's wording will stand up in court.
+
+=head2 How can I compile my Perl program into byte code or C?
+
+Malcolm Beattie has written a multifunction backend compiler,
+available from CPAN, that can do both these things. It is included
+in the perl5.005 release, but is still considered experimental.
+This means it's fun to play with if you're a programmer but not
+really for people looking for turn-key solutions.
+
+Merely compiling into C does not in and of itself guarantee that your
+code will run very much faster. That's because except for lucky cases
+where a lot of native type inferencing is possible, the normal Perl
+run-time system is still present and so your program will take just as
+long to run and be just as big. Most programs save little more than
+compilation time, leaving execution no more than 10-30% faster. A few
+rare programs actually benefit significantly (even running several times
+faster), but this takes some tweaking of your code.
+
+You'll probably be astonished to learn that the current version of the
+compiler generates a compiled form of your script whose executable is
+just as big as the original perl executable, and then some. That's
+because as currently written, all programs are prepared for a full
+eval() statement. You can tremendously reduce this cost by building a
+shared I<libperl.so> library and linking against that. See the
+F<INSTALL> podfile in the Perl source distribution for details. If
+you link your main perl binary with this, it will make it minuscule.
+For example, on one author's system, F</usr/bin/perl> is only 11k in
+size!
+
+In general, the compiler will do nothing to make a Perl program smaller,
+faster, more portable, or more secure. In fact, it can make your
+situation worse. The executable will be bigger, your VM system may take
+longer to load the whole thing, the binary is fragile and hard to fix,
+and compilation never stopped software piracy in the form of crackers,
+viruses, or bootleggers. The real advantage of the compiler is merely
+packaging, and once you see the size of what it makes (well, unless
+you use a shared I<libperl.so>), you'll probably want a complete
+Perl install anyway.
+
+=head2 How can I compile Perl into Java?
+
+You can also integrate Java and Perl with the
+Perl Resource Kit from O'Reilly and Associates. See
+http://www.oreilly.com/catalog/prkunix/ .
+
+Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in
+development, allows Perl code to be called from Java. See jpl/README
+in the Perl source tree.
+
+=head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
+
+For OS/2 just use
+
+ extproc perl -S -your_switches
+
+as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's
+`extproc' handling). For DOS one should first invent a corresponding
+batch file and codify it in C<ALTERNATIVE_SHEBANG> (see the
+F<INSTALL> file in the source distribution for more information).
+
+The Win95/NT installation, when using the ActiveState port of Perl,
+will modify the Registry to associate the C<.pl> extension with the
+perl interpreter. If you install another port, perhaps even building
+your own Win95/NT Perl from the standard sources by using a Windows port
+of gcc (e.g., with cygwin or mingw32), then you'll have to modify
+the Registry yourself. In addition to associating C<.pl> with the
+interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them
+run the program C<install-linux.pl> merely by typing C<install-linux>.
+
+Macintosh Perl programs will have the appropriate Creator and
+Type, so that double-clicking them will invoke the Perl application.
+
+I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just
+throw the perl interpreter into your cgi-bin directory, in order to
+get your programs working for a web server. This is an EXTREMELY big
+security risk. Take the time to figure out how to do it correctly.
+
+=head2 Can I write useful Perl programs on the command line?
+
+Yes. Read L<perlrun> for more information. Some examples follow.
+(These assume standard Unix shell quoting rules.)
+
+ # sum first and last fields
+ perl -lane 'print $F[0] + $F[-1]' *
+
+ # identify text files
+ perl -le 'for(@ARGV) {print if -f && -T _}' *
+
+ # remove (most) comments from C program
+ perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
+
+ # make file a month younger than today, defeating reaper daemons
+ perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *
+
+ # find first unused uid
+ perl -le '$i++ while getpwuid($i); print $i'
+
+ # display reasonable manpath
+ echo $PATH | perl -nl -072 -e '
+ s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
+
+OK, the last one was actually an Obfuscated Perl Contest entry. :-)
+
+=head2 Why don't Perl one-liners work on my DOS/Mac/VMS system?
+
+The problem is usually that the command interpreters on those systems
+have rather different ideas about quoting than the Unix shells under
+which the one-liners were created. On some systems, you may have to
+change single-quotes to double ones, which you must I<NOT> do on Unix
+or Plan9 systems. You might also have to change a single % to a %%.
+
+For example:
+
+ # Unix
+ perl -e 'print "Hello world\n"'
+
+ # DOS, etc.
+ perl -e "print \"Hello world\n\""
+
+ # Mac
+ print "Hello world\n"
+ (then Run "Myscript" or Shift-Command-R)
+
+ # VMS
+ perl -e "print ""Hello world\n"""
+
+The problem is that none of these examples are reliable: they depend on the
+command interpreter. Under Unix, the first two often work. Under DOS,
+it's entirely possible that neither works. If 4DOS was the command shell,
+you'd probably have better luck like this:
+
+ perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
+
+Under the Mac, it depends which environment you are using. The MacPerl
+shell, or MPW, is much like Unix shells in its support for several
+quoting variants, except that it makes free use of the Mac's non-ASCII
+characters as control characters.
+
+Using qq(), q(), and qx(), instead of "double quotes", 'single
+quotes', and `backticks`, may make one-liners easier to write.
+
+There is no general solution to all of this. It is a mess, pure and
+simple. Sucks to be away from Unix, huh? :-)
+
+[Some of this answer was contributed by Kenneth Albanowski.]
+
+=head2 Where can I learn about CGI or Web programming in Perl?
+
+For modules, get the CGI or LWP modules from CPAN. For textbooks,
+see the two especially dedicated to web stuff in the question on
+books. For problems and questions related to the web, like ``Why
+do I get 500 Errors'' or ``Why doesn't it run from the browser right
+when it runs fine on the command line'', see these sources:
+
+ WWW Security FAQ
+ http://www.w3.org/Security/Faq/
+
+ Web FAQ
+ http://www.boutell.com/faq/
+
+ CGI FAQ
+ http://www.webthing.com/tutorials/cgifaq.html
+
+ HTTP Spec
+ http://www.w3.org/pub/WWW/Protocols/HTTP/
+
+ HTML Spec
+ http://www.w3.org/TR/REC-html40/
+ http://www.w3.org/pub/WWW/MarkUp/
+
+ CGI Spec
+ http://www.w3.org/CGI/
+
+ CGI Security FAQ
+ http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt
+
+=head2 Where can I learn about object-oriented Perl programming?
+
+A good place to start is L<perltoot>, and you can use L<perlobj>,
+L<perlboot>, and L<perlbot> for reference. Perltoot didn't come out
+until the 5.004 release; you can get a copy (in pod, html, or
+postscript) from http://www.perl.com/CPAN/doc/FMTEYEWTK/ .
+
+=head2 Where can I learn about linking C with Perl? [h2xs, xsubpp]
+
+If you want to call C from Perl, start with L<perlxstut>,
+moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to
+call Perl from C, then read L<perlembed>, L<perlcall>, and
+L<perlguts>. Don't forget that you can learn a lot from looking at
+how the authors of existing extension modules wrote their code and
+solved their problems.
+
+=head2 I've read perlembed, perlguts, etc., but I can't embed perl in
+my C program; what am I doing wrong?
+
+Download the ExtUtils::Embed kit from CPAN and run `make test'. If
+the tests pass, read the pods again and again and again. If they
+fail, see L<perlbug> and send a bug report with the output of
+C<make test TEST_VERBOSE=1> along with C<perl -V>.
+
+=head2 When I tried to run my script, I got this message. What does it
+mean?
+
+A complete list of Perl's error messages and warnings with explanatory
+text can be found in L<perldiag>. You can also use the splain program
+(distributed with Perl) to explain the error messages:
+
+ perl program 2>diag.out
+ splain [-v] [-p] diag.out
+
+or change your program to explain the messages for you:
+
+ use diagnostics;
+
+or
+
+ use diagnostics -verbose;
+
+=head2 What's MakeMaker?
+
+This module (part of the standard Perl distribution) is designed to
+write a Makefile for an extension module from a Makefile.PL. For more
+information, see L<ExtUtils::MakeMaker>.
+
+=head1 AUTHOR AND COPYRIGHT
+
+Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington.
+All rights reserved.
+
+When included as an integrated part of the Standard Distribution
+of Perl or of its documentation (printed or otherwise), this works is
+covered under Perl's Artistic License. For separate distributions of
+all or part of this FAQ outside of that, see L<perlfaq>.
+
+Irrespective of its distribution, all code examples here are in the public
+domain. You are permitted and encouraged to use this code and any
+derivatives thereof in your own programs for fun or for profit as you
+see fit. A simple comment in the code giving credit to the FAQ would
+be courteous but is not required.
projects / dh-make-perl / blobdiff