perlfaq.pod

source of perl for linux application,

=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