=head1 NAME
-perlfaq3 - Programming Tools ($Revision: 1.41 $, $Date: 2004/11/03 22:45:32 $)
+perlfaq3 - Programming Tools
=head1 DESCRIPTION
=head2 How can I use Perl interactively?
The typical approach uses the Perl debugger, described in the
-perldebug(1) manpage, on an ``empty'' program, like this:
+perldebug(1) manpage, on an "empty" program, like this:
perl -de 42
=head2 Is there a Perl shell?
-The psh (Perl sh) is currently at version 1.8. The Perl Shell is a
-shell that combines the interactive nature of a Unix shell with the
-power of Perl. The goal is a full featured shell that behaves as
-expected for normal shell activity and uses Perl syntax and
-functionality for control-flow statements and other things.
-You can get psh at http://www.focusresearch.com/gregor/psh/ .
+The psh (Perl sh) is currently at version 1.8. The Perl Shell is a shell
+that combines the interactive nature of a Unix shell with the power of
+Perl. The goal is a full featured shell that behaves as expected for
+normal shell activity and uses Perl syntax and functionality for
+control-flow statements and other things. You can get psh at
+http://sourceforge.net/projects/psh/ .
Zoidberg is a similar project and provides a shell written in perl,
configured in perl and operated in perl. It is intended as a login shell
-and development environment. It can be found at http://zoidberg.sf.net/
+and development environment. It can be found at
+http://pardus-larus.student.utwente.nl/~pardus/projects/zoidberg/
or your local CPAN mirror.
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.
+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 find which modules are installed on my system?
-You can use the ExtUtils::Installed module to show all
-installed distributions, although it can take awhile to do
-its magic. The standard library which comes with Perl just
-shows up as "Perl" (although you can get those with
-Module::CoreList).
+From the command line, you can use the C<cpan> command's C<-l> switch:
+
+ $ cpan -l
+
+You can also use C<cpan>'s C<-a> switch to create an autobundle file
+that C<CPAN.pm> understands and cna use to re-install every module:
+
+ $ cpan -a
+
+Inside a Perl program, you can use the ExtUtils::Installed module to
+show all installed distributions, although it can take awhile to do
+its magic. The standard library which comes with Perl just shows up
+as "Perl" (although you can get those with Module::CoreList).
use ExtUtils::Installed;
use File::Find::Rule;
- my @files = File::Find::Rule->file()->name( '*.pm' )->in( @INC );
+ my @files = File::Find::Rule->
+ extras({follow => 1})->
+ file()->
+ name( '*.pm' )->
+ in( @INC )
+ ;
If you do not have that module, you can do the same thing
with File::Find which is part of the standard library.
- use File::Find;
- my @files;
-
- find sub { push @files, $File::Find::name if -f _ && /\.pm$/ },
- @INC;
+ use File::Find;
+ my @files;
+
+ find(
+ {
+ wanted => sub {
+ push @files, $File::Find::fullname
+ if -f $File::Find::fullname && /\.pm$/
+ },
+ follow => 1,
+ follow_skip => 2,
+ },
+ @INC
+ );
print join "\n", @files;
If you cannot read the documentation, the module might not
have any (in rare cases).
- prompt% perldoc Module::Name
+ $ perldoc Module::Name
You can also try to include the module in a one-liner to see if
perl finds it.
- perl -MModule::Name -e1
+ $ perl -MModule::Name -e1
=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.
+(contributed by brian d foy)
+
+Before you do anything else, you can help yourself by ensuring that
+you let Perl tell you about problem areas in your code. By turning
+on warnings and strictures, you can head off many problems before
+they get too big. You can find out more about these in L<strict>
+and L<warnings>.
-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>.
+ #!/usr/bin/perl
+ use strict;
+ use warnings;
-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.
+Beyond that, the simplest debugger is the C<print> function. Use it
+to look at values as you run your program:
- open(FH, "> /etc/cantwrite")
- or die "Couldn't write to /etc/cantwrite: $!\n";
+ print STDERR "The value is [$value]\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>.
+The C<Data::Dumper> module can pretty-print Perl data structures:
-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.
+ use Data::Dumper qw( Dumper );
+ print STDERR "The hash is " . Dumper( \%hash ) . "\n";
+
+Perl comes with an interactive debugger, which you can start with the
+C<-d> switch. It's fully explained in L<perldebug>.
+
+If you'd like a graphical user interface and you have Tk, you can use
+C<ptkdb>. It's on CPAN and available for free.
+
+If you need something much more sophisticated and controllable, Leon
+Brocard's Devel::ebug (which you can call with the -D switch as -Debug)
+gives you the programmatic hooks into everything you need to write your
+own (without too much pain and suffering).
+
+You can also use a commercial debugger such as Affrus (Mac OS X), Komodo
+from Activestate (Windows and Mac OS X), or EPIC (most platforms).
=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.
+(contributed by brian d foy, updated Fri Jul 25 12:22:26 PDT 2008)
+
+The C<Devel> namespace has several modules which you can use to
+profile your Perl programs. The C<Devel::DProf> module comes with Perl
+and you can invoke it with the C<-d> switch:
-Here's a sample use of Benchmark:
+ perl -d:DProf program.pl
- use Benchmark;
+After running your program under C<DProf>, you'll get a F<tmon.out> file
+with the profile data. To look at the data, you can turn it into a
+human-readable report with the C<dprofpp> program that comes with
+C<Devel::DProf>.
- @junk = `cat /etc/motd`;
- $count = 10_000;
+ dprofpp
- timethese($count, {
- 'map' => sub { my @a = @junk;
- map { s/a/b/ } @a;
- return @a },
- 'for' => sub { my @a = @junk;
- for (@a) { s/a/b/ };
- return @a },
- });
+You can also do the profiling and reporting in one step with the C<-p>
+switch to <dprofpp>:
-This is what it prints (on one machine--your results will be dependent
-on your hardware, operating system, and the load on your machine):
+ dprofpp -p program.pl
- 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)
+The C<Devel::NYTProf> (New York Times Profiler) does both statement
+and subroutine profiling. It's available from CPAN and you also invoke
+it with the C<-d> switch:
-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.
+ perl -d:NYTProf some_perl.pl
+
+Like C<DProf>, it creates a database of the profile information that you
+can turn into reports. The C<nytprofhtml> command turns the data into
+an HTML report similar to the C<Devel::Cover> report:
+
+ nytprofhtml
+
+CPAN has several other profilers that you can invoke in the same
+fashion. You might also be interested in using the C<Benchmark> to
+measure and compare code snippets.
+
+You can read more about profiling in I<Programming Perl>, chapter 20,
+or I<Mastering Perl>, chapter 5.
+
+L<perldebguts> documents creating a custom debugger if you need to
+create a special sort of profiler. brian d foy describes the process
+in I<The Perl Journal>, "Creating a Perl Debugger",
+http://www.ddj.com/184404522 , and "Profiling in Perl"
+http://www.ddj.com/184404580 .
+
+Perl.com has two interesting articles on profiling: "Profiling Perl",
+by Simon Cozens, http://www.perl.com/lpt/a/850 and "Debugging and
+Profiling mod_perl Applications", by Frank Wiles,
+http://www.perl.com/pub/a/2006/02/09/debug_mod_perl.html .
+
+Randal L. Schwartz writes about profiling in "Speeding up Your Perl
+Programs" for I<Unix Review>,
+http://www.stonehenge.com/merlyn/UnixReview/col49.html , and "Profiling
+in Template Toolkit via Overriding" for I<Linux Magazine>,
+http://www.stonehenge.com/merlyn/LinuxMag/col75.html .
=head2 How do I cross-reference my Perl programs?
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. A more complete example, with comments, can be found at
+for indenting, ^D is for undenting, and ^O is for blockdenting--as
+it were. A more complete example, with comments, can be found at
http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz
The a2ps http://www-inf.enst.fr/%7Edemaille/a2ps/black+white.ps.gz does
lots of things related to generating nicely printed output of
-documents, as does enscript at http://people.ssh.fi/mtr/genscript/ .
+documents.
=head2 Is there a ctags for Perl?
-Recent versions of ctags do much more than older versions did.
-EXUBERANT CTAGS is available from http://ctags.sourceforge.net/
-and does a good job of making tags files for perl code.
+(contributed by brian d foy)
+
+Ctags uses an index to quickly find things in source code, and many
+popular editors support ctags for several different languages,
+including Perl.
-There is also a simple one at
-http://www.cpan.org/authors/id/TOMC/scripts/ptags.gz which may do
-the trick. It can be easy to hack this into what you want.
+Exuberent ctags supports Perl: http://ctags.sourceforge.net/
+
+You might also try pltags: http://www.mscha.com/pltags.zip
=head2 Is there an IDE or Windows Perl Editor?
=item Eclipse
-The Eclipse Perl Integration Project integrates Perl
+http://e-p-i-c.sf.net/
+
+The Eclipse Perl Integration Project integrates Perl
editing/debugging with Eclipse.
-The website for the project is http://e-p-i-c.sf.net/
+=item Enginsite
+
+http://www.enginsite.com/
+
+Perl Editor by EngInSite is a complete integrated development
+environment (IDE) for creating, testing, and debugging Perl scripts;
+the tool runs on Windows 9x/NT/2000/XP or later.
=item Komodo
+http://www.ActiveState.com/Products/Komodo/
+
ActiveState's cross-platform (as of October 2004, that's Windows, Linux,
and Solaris), multi-language IDE has Perl support, including a regular expression
-debugger and remote debugging
-( http://www.ActiveState.com/Products/Komodo/ ).
+debugger and remote debugging.
=item Open Perl IDE
-( http://open-perl-ide.sourceforge.net/ )
+http://open-perl-ide.sourceforge.net/
+
Open Perl IDE is an integrated development environment for writing
and debugging Perl scripts with ActiveState's ActivePerl distribution
under Windows 95/98/NT/2000.
=item OptiPerl
-( http://www.optiperl.com/ ) is a Windows IDE with simulated CGI
-environment, including debugger and syntax highlighting editor.
-
-=item PerlBuilder
-
-( http://www.solutionsoft.com/perl.htm ) is an integrated development
-environment for Windows that supports Perl development.
-
-=item visiPerl+
-
-( http://helpconsulting.net/visiperl/ )
-From Help Consulting, for Windows.
-
-=item Visual Perl
-
-( http://www.activestate.com/Products/Visual_Perl/ )
-Visual Perl is a Visual Studio.NET plug-in from ActiveState.
-
-
-=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.
-
-If you are using Windows, you can use any editor that lets
-you work with plain text, such as NotePad or WordPad. Word
-processors, such as Microsoft Word or WordPerfect, typically
-do not work since they insert all sorts of behind-the-scenes
-information, although some allow you to save files as "Text
-Only". You can also download text editors designed
-specifically for programming, such as Textpad
-( http://www.textpad.com/ ) and UltraEdit
-( http://www.ultraedit.com/ ), among others.
-
-If you are using MacOS, the same concerns apply. MacPerl
-(for Classic environments) comes with a simple editor.
-Popular external editors are BBEdit ( http://www.bbedit.com/ )
-or Alpha ( http://www.his.com/~jguyer/Alpha/Alpha8.html ). MacOS X users can
-use Unix editors as well.
-
-=over 4
-
-=item GNU Emacs
-
-http://www.gnu.org/software/emacs/windows/ntemacs.html
-
-=item MicroEMACS
-
-http://www.microemacs.de/
-
-=item XEmacs
-
-http://www.xemacs.org/Download/index.html
-
-=item Jed
-
-http://space.mit.edu/~davis/jed/
-
-=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://dickey.his.com/vile/vile.html
-
-=item Vim
-
-http://www.vim.org/
-
-=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.borland.com/codewright/
-
-=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/ ) 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
+http://www.optiperl.com/
-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/ )
+OptiPerl is a Windows IDE with simulated CGI environment, including
+debugger and syntax highlighting editor.
-=item Tcsh
+=item Padre
-ftp://ftp.astron.com/pub/tcsh/ , see also
-http://www.primate.wisc.edu/software/csh-tcsh-book/
+http://padre.perlide.org/
-=item Zsh
+Padre is cross-platform IDE for Perl written in Perl using the the wxWidgets
+to provide a native look and feel. It's open source under the Artistic
+License.
-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 Affrus
-
-is a full Perl development enivornment with full debugger support (
-http://www.latenightsw.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://www.his.com/~jguyer/Alpha/Alpha8.html ).
-
-=item BBEdit and BBEdit Lite
-
-are text editors for Mac OS that have a Perl sensitivity mode
-( http://web.barebones.com/ ).
-
-
-=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.cpan.org/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.cpan.org/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.cpan.org/authors/Tom_Christiansen/scripts/rep.gz ;
-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.cpan.org/modules/by-category/08_User_Interfaces/
-
-Invaluable for Perl/Tk programming are the Perl/Tk FAQ at
-http://phaseit.net/claird/comp.lang.perl.tk/ptkFAQ.html , the Perl/Tk Reference
-Guide available at
-http://www.cpan.org/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.cpan.org/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
-module, which is curses-based, can help with this.
-
-=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
-I<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. You will probably want to
-read the answer to the earlier question ``How do I profile my Perl
-programs?'' if you haven't done so already.
-
-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).
-
-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.
-
-The undump program was an ancient attempt to speed up 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>.
-
-Of course, the best way to save memory is to not do anything to waste
-it in the first place. Good programming practices can go a long way
-toward this:
-
-=over 4
-
-=item * Don't slurp!
-
-Don't read an entire file into memory if you can process it line
-by line. Or more concretely, use a loop like this:
-
- #
- # Good Idea
- #
- while (<FILE>) {
- # ...
- }
-
-instead of this:
-
- #
- # Bad Idea
- #
- @data = <FILE>;
- foreach (@data) {
- # ...
- }
-
-When the files you're processing are small, it doesn't much matter which
-way you do it, but it makes a huge difference when they start getting
-larger.
-
-=item * Use map and grep selectively
-
-Remember that both map and grep expect a LIST argument, so doing this:
-
- @wanted = grep {/pattern/} <FILE>;
-
-will cause the entire file to be slurped. For large files, it's better
-to loop:
-
- while (<FILE>) {
- push(@wanted, $_) if /pattern/;
- }
-
-=item * Avoid unnecessary quotes and stringification
-
-Don't quote large strings unless absolutely necessary:
-
- my $copy = "$large_string";
-
-makes 2 copies of $large_string (one for $copy and another for the
-quotes), whereas
-
- my $copy = $large_string;
-
-only makes one copy.
+=item PerlBuilder
-Ditto for stringifying large arrays:
+http://www.solutionsoft.com/perl.htm
- {
- local $, = "\n";
- print @big_array;
- }
+PerlBuilder is an integrated development environment for Windows that
+supports Perl development.
-is much more memory-efficient than either
+=item visiPerl+
- print join "\n", @big_array;
+http://helpconsulting.net/visiperl/
-or
+From Help Consulting, for Windows.
- {
- local $" = "\n";
- print "@big_array";
- }
+=item Visual Perl
+http://www.activestate.com/Products/Visual_Perl/
-=item * Pass by reference
+Visual Perl is a Visual Studio.NET plug-in from ActiveState.
-Pass arrays and hashes by reference, not by value. For one thing, it's
-the only way to pass multiple lists or hashes (or both) in a single
-call/return. It also avoids creating a copy of all the contents. This
-requires some judgment, however, because any changes will be propagated
-back to the original data. If you really want to mangle (er, modify) a
-copy, you'll have to sacrifice the memory needed to make one.
+=item Zeus
-=item * Tie large variables to disk.
+http://www.zeusedit.com/lookmain.html
-For "big" data stores (i.e. ones that exceed available memory) consider
-using one of the DB modules to store it on disk instead of in RAM. This
-will incur a penalty in access time, but that's probably better than
-causing your hard disk to thrash due to massive swapping.
+Zeus for Window is another Win32 multi-language editor/IDE
+that comes with support for Perl:
=back
-=head2 Is it safe to return a reference to local or lexical data?
-
-Yes. Perl's garbage collection system takes care of this so
-everything works out right.
-
- sub makeone {
- my @a = ( 1 .. 10 );
- return \@a;
- }
-
- for ( 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 usually 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, systems that
-use mmap(2) for allocating large chunks of memory) can
-reclaim memory that is no longer used, but on such systems,
-perl must be configured and compiled to use the OS's malloc,
-not perl's.
-
-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.cpan.org/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 (Starting from Perl
-5.8 the Filter::Simple and Filter::Util::Call modules are included in
-the standard distribution), 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).
-
-It is very easy to recover the source of Perl programs. You simply
-feed the program to the perl interpreter and use the modules in
-the B:: hierarchy. The B::Deparse module should be able to
-defeat most attempts to hide source. Again, this is not
-unique to 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 Media. 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<ALTERNATE_SHEBANG> (see the
-F<dosish.h> 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)
-
- # MPW
- perl -e 'print "Hello world\n"'
-
- # 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.
-
-[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 the troubleshooting
-guides and references in L<perlfaq9> or in the CGI MetaFAQ:
-
- http://www.perl.org/CGI_MetaFAQ.html
-
-=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>, L<perltoot>, L<perltooc>, and L<perlbot> for reference.
-(If you are using really old Perl, you may not have all of these,
-try http://www.perldoc.com/ , but consider upgrading your perl.)
-
-A good book on OO on Perl is the "Object-Oriented Perl"
-by Damian Conway from Manning Publications,
-http://www.manning.com/Conway/index.html
-
-=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) 1997-2002 Tom Christiansen and Nathan Torkington.
-All rights reserved.
-
-This documentation is free; you can redistribute it and/or modify it
-under the same terms as Perl itself.
+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.
-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.
+If you are using Windows, you can use any editor that lets you work
+with plain text, such as NotePad or WordPad. Word processors, such as
+Microsoft Word or WordPerfect, typically do not work since they insert
+all sorts of behind-the-scenes information, although some allow you to
+save files as "Text Only". You can also download te
\ No newline at end of file
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