=head1 NAME
-perlfaq3 - Programming Tools ($Revision: 1.38 $, $Date: 1999/05/23 16:08:30 $)
+perlfaq3 - Programming Tools ($Revision: 1.22 $, $Date: 2002/05/06 13:11:13 $)
=head1 DESCRIPTION
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)
+ Various http://www.cpan.org/misc/olddoc/FMTEYEWTK.tgz
+ (not a man-page but still useful, a collection
+ of various essays on Perl techniques)
A crude table of contents for the Perl manpage set is found in L<perltoc>.
=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.
+In general, not yet. There is psh available at
+
+ http://www.focusresearch.com/gregor/psh
+
+Which includes the following description:
+
+ The Perl Shell is a shell that combines the interactive nature
+ of a Unix shell with the power of Perl. The goal is to eventually
+ have a full featured shell that behaves as expected for normal
+ shell activity. But, the Perl Shell will use Perl syntax and
+ functionality for control-flow statements and other things.
+
+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?
=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.
+The B::Xref module 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:
+Perltidy is a Perl script which indents and reformats Perl scripts
+to make them easier to read by trying to follow the rules of the
+L<perlstyle>. If you write Perl scripts, or spend much time reading
+them, you will probably find it useful. It is available at
+http://perltidy.sourceforge.net
+
+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 Christiansen and many other VI users swear 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
+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.
+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 at http://www.infres.enst.fr/%7Edemaille/a2ps/ does lots of things
-related to generating nicely printed output of documents.
+The a2ps http://www-inf.enst.fr/%7Edemaille/a2ps/black+white.ps does
+lots of things related to generating nicely printed output of
+documents, as does enscript at http://people.ssh.fi/mtr/genscript/ .
=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.
+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.
+
+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.
=head2 Is there an IDE or Windows Perl Editor?
ActiveState's cross-platform (as of April 2001 Windows and Linux),
multi-language IDE has Perl support, including a regular expression
debugger and remote debugging
-(http://www.ActiveState.com/Products/Komodo/index.html). (Visual
+( 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)).
+( http://www.ActiveState.com/Products/VisualPerl/index.html )).
=item The Object System
-(http://www.castlelink.co.uk/object_system/) is a Perl web
+( http://www.castlelink.co.uk/object_system/ ) is a Perl web
applications development IDE, apparently for any platform
that runs Perl.
=item PerlBuilder
-(http://www.solutionsoft.com/perl.htm) is an integrated development
+( 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 OptiPerl
+
+( http://www.optiperl.com/ ) is a Windows IDE with simulated CGI
+environment, including debugger and syntax highlighting editor.
+
=back
For Windows there's also the
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
+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 Mac OS, 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.kelehers.org/alpha/ ). Mac OS X users can
+use Unix editors as well.
=over 4
=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
+ 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
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
+( 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
+( 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
=item Bash
-from the Cygwin package (http://sources.redhat.com/cygwin/)
+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/)
+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
+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/
+ftp://ftp.blarg.net/users/amol/zsh/ , see also http://www.zsh.org/
=back
=item BBEdit and BBEdit Lite
are text editors for Mac OS that have a Perl sensitivity mode
-(http://web.barebones.com/).
+( 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/).
+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/).
+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 ,
+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.perl.com/CPAN/src/misc.
+with an embedded Perl interpreter--see http://www.cpan.org/src/misc/ .
=head2 Where can I get perl-mode for emacs?
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;
+directory http://www.cpan.org/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>.
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/
+directory http://www.cpan.org/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
+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.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
+The http://www.cpan.org/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
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.
+
+Ditto for stringifying large arrays:
+
+ {
+ local $, = "\n";
+ print @big_array;
+ }
+
+is much more memory-efficient than either
+
+ print join "\n", @big_array;
+
+or
+
+ {
+ local $" = "\n";
+ print "@big_array";
+ }
+
+
+=item * Pass by reference
+
+Pass arrays and hashes by reference, not by value. For one thing, it's
+the only way to pass multiple lists or hashes (or both) in a single
+call/return. It also avoids creating a copy of all the contents. This
+requires some judgment, however, because any changes will be propagated
+back to the original data. If you really want to mangle (er, modify) a
+copy, you'll have to sacrifice the memory needed to make one.
+
+=item * Tie large variables to disk.
+
+For "big" data stores (i.e. ones that exceed available memory) consider
+using one of the DB modules to store it on disk instead of in RAM. This
+will incur a penalty in access time, but that's probably better than
+causing your hard disk to thrash due to massive swapping.
+
+=back
+
=head2 Is it unsafe to return a pointer to local data?
No, Perl's garbage collection system takes care of this.
=head2 How can I free an array or hash so my program shrinks?
-You can't. On most operating systems, memory allocated to a program
-can never be returned to the system. That's why long-running programs
-sometimes re-exec themselves. Some operating systems (notably,
-FreeBSD and Linux) allegedly reclaim large chunks of memory that is no
-longer used, but it doesn't appear to happen with Perl (yet). The Mac
-appears to be the only platform that will reliably (albeit, slowly)
-return memory to the OS.
-
-We've had reports that on Linux (Redhat 5.1) on Intel, C<undef
-$scalar> will return memory to the system, while on Solaris 2.6 it
-won't. In general, try it yourself and see.
+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
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
+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
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
+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/ .
+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/ )
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"""
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? :-)
+There is no general solution to all of this. It is a mess.
[Some of this answer was contributed by Kenneth Albanowski.]
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:
+when it runs fine on the command line'', see the troubleshooting
+guides and references in L<perlfaq9> or in the CGI MetaFAQ:
- 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
+ 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>, 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/ .
+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]
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?
+=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
=head1 AUTHOR AND COPYRIGHT
-Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington.
+Copyright (c) 1997-2002 Tom Christiansen and Nathan Torkington.
All rights reserved.
This documentation is free; you can redistribute it and/or modify it
https://perl5.git.perl.org / perl5.git / blobdiff