=head1 NAME
-perlfaq3 - Programming Tools ($Revision: 1.38 $, $Date: 1999/05/23 16:08:30 $)
+perlfaq3 - Programming Tools ($Revision: 1.4 $, $Date: 2001/10/02 19:42:02 $)
=head1 DESCRIPTION
=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 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 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
+as it were. 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
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 * 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 that
+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.
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>.
+This documentation is free; you can redistribute it and/or modify it
+under the same terms as Perl itself.
Irrespective of its distribution, all code examples here are in the public
domain. You are permitted and encouraged to use this code and any
projects / p5sagit/p5-mst-13.2.git / blobdiff