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authorSiep Kroonenberg <siepo@cybercomm.nl>2011-02-17 17:31:37 +0000
committerSiep Kroonenberg <siepo@cybercomm.nl>2011-02-17 17:31:37 +0000
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tree5185d4773197a8bc419342ca26b1db30dc992b5a /Master/tlpkg/tlperl/lib/pods/perlfaq3.pod
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New tlperl part XI
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+=head1 NAME
+
+perlfaq3 - Programming Tools
+
+=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 manpages? 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.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 How can I use Perl interactively?
+
+The typical approach uses the Perl debugger, described in the
+C<perldebug(1)> manpage, 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?
+
+The C<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 C<psh> at
+http://sourceforge.net/projects/psh/ .
+
+C<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://pardus-larus.student.utwente.nl/~pardus/projects/zoidberg/
+or your local CPAN mirror.
+
+The C<Shell.pm> module (distributed with Perl) makes Perl try commands
+which aren't part of the Perl language as shell commands. C<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?
+
+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 can use to re-install every module:
+
+ $ cpan -a
+
+Inside a Perl program, you can use the C<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 C<Module::CoreList>).
+
+ use ExtUtils::Installed;
+
+ my $inst = ExtUtils::Installed->new();
+ my @modules = $inst->modules();
+
+If you want a list of all of the Perl module filenames, you
+can use C<File::Find::Rule>:
+
+ use File::Find::Rule;
+
+ 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 C<File::Find> which is part of the standard library:
+
+ 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 simply need to quickly check to see if a module is
+available, you can check for its documentation. If you can
+read the documentation the module is most likely installed.
+If you cannot read the documentation, the module might not
+have any (in rare cases):
+
+ $ 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
+
+=head2 How do I debug my Perl programs?
+
+(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>.
+
+ #!/usr/bin/perl
+ use strict;
+ use warnings;
+
+Beyond that, the simplest debugger is the C<print> function. Use it
+to look at values as you run your program:
+
+ print STDERR "The value is [$value]\n";
+
+The C<Data::Dumper> module can pretty-print Perl data structures:
+
+ 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 C<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 C<Devel::ebug> (which you can call with the C<-D> switch as C<-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?
+
+(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:
+
+ perl -d:DProf program.pl
+
+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>.
+
+ dprofpp
+
+You can also do the profiling and reporting in one step with the C<-p>
+switch to C<dprofpp>:
+
+ dprofpp -p program.pl
+
+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:
+
+ 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?
+
+The C<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?
+
+C<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
+
+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
+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.
+
+=head2 Is there a ctags for Perl?
+
+(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.
+
+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?
+
+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 an IDE, check the following (in alphabetical order, not
+order of preference):
+
+=over 4
+
+=item Eclipse
+
+http://e-p-i-c.sf.net/
+
+The Eclipse Perl Integration Project integrates Perl
+editing/debugging with Eclipse.
+
+=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.
+
+=item Notepad++
+
+http://notepad-plus.sourceforge.net/
+
+=item Open Perl IDE
+
+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/
+
+OptiPerl is a Windows IDE with simulated CGI environment, including
+debugger and syntax highlighting editor.
+
+=item Padre
+
+http://padre.perlide.org/
+
+Padre is cross-platform IDE for Perl written in Perl using wxWidgets to provide
+a native look and feel. It's open source under the Artistic License.
+
+=item PerlBuilder
+
+http://www.solutionsoft.com/perl.htm
+
+PerlBuilder 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.
+
+=item Zeus
+
+http://www.zeusedit.com/lookmain.html
+
+Zeus for Window is another Win32 multi-language editor/IDE
+that comes with support for Perl:
+
+=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/IDEs that support Perl:
+
+=over 4
+
+=item Codewright
+
+http://www.borland.com/codewright/
+
+=item MultiEdit
+
+http://www.MultiEdit.com/
+
+=item SlickEdit
+
+http://www.slickedit.com/
+
+=item ConTEXT
+
+http://www.contexteditor.org/
+
+=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://ptkdb.sourceforge.net/ ) 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
+
+from the MKS Toolkit ( http://www.mkssoftware.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
+
+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 General 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 environment 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
+
+=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 or cperl-mode for emacs?
+X<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.
+
+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.
+
+For CPerlMode, see http://www.emacswiki.org/cgi-bin/wiki/CPerlMode
+
+=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 write a GUI (X, Tk, Gtk, etc.) in Perl?
+X<GUI> X<Tk> X<Wx> X<WxWidgets> X<Gtk> X<Gtk2> X<CamelBones> X<Qt>
+
+(contributed by Ben Morrow)
+
+There are a number of modules which let you write GUIs in Perl. Most
+GUI toolkits have a perl interface: an incomplete list follows.
+
+=over 4
+
+=item Tk
+
+This works under Unix and Windows, and the current version doesn't
+look half as bad under Windows as it used to. Some of the gui elements
+still don't 'feel' quite right, though. The interface is very natural
+and 'perlish', making it easy to use in small scripts that just need a
+simple gui. It hasn't been updated in a while.
+
+=item Wx
+
+This is a Perl binding for the cross-platform wxWidgets toolkit
+( http://www.wxwidgets.org ). It works under Unix, Win32 and Mac OS X,
+using native widgets (Gtk under Unix). The interface follows the C++
+interface closely, but the documentation is a little sparse for someone
+who doesn't know the library, mostly just referring you to the C++
+documentation.
+
+=item Gtk and Gtk2
+
+These are Perl bindings for the Gtk toolkit ( http://www.gtk.org ). The
+interface changed significantly between versions 1 and 2 so they have
+separate Perl modules. It runs under Unix, Win32 and Mac OS X (currently
+it requires an X server on Mac OS, but a 'native' port is underway), and
+the widgets look the same on every plaform: i.e., they don't match the
+native widgets. As with Wx, the Perl bindings follow the C API closely,
+and the documentation requires you to read the C documentation to
+understand it.
+
+=item Win32::GUI
+
+This provides access to most of the Win32 GUI widgets from Perl.
+Obviously, it only runs under Win32, and uses native widgets. The Perl
+interface doesn't really follow the C interface: it's been made more
+Perlish, and the documentation is pretty good. More advanced stuff may
+require familiarity with the C Win32 APIs, or reference to MSDN.
+
+=item CamelBones
+
+CamelBones ( http://camelbones.sourceforge.net ) is a Perl interface to
+Mac OS X's Cocoa GUI toolkit, and as such can be used to produce native
+GUIs on Mac OS X. It's not on CPAN, as it requires frameworks that
+CPAN.pm doesn't know how to install, but installation is via the
+standard OSX package installer. The Perl API is, again, very close to
+the ObjC API it's wrapping, and the documentation just tells you how to
+translate from one to the other.
+
+=item Qt
+
+There is a Perl interface to TrollTech's Qt toolkit, but it does not
+appear to be maintained.
+
+=item Athena
+
+Sx is an interface to the Athena widget set which comes with X, but
+again it appears not to be much used nowadays.
+
+=back
+
+=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.
+
+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 judgement, 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 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?
+
+(contributed by Michael Carman)
+
+You usually can't. Memory allocated to lexicals (i.e. my() variables)
+cannot be reclaimed or reused even if they go out of scope. It is
+reserved in case the variables come back into scope. Memory allocated
+to global variables can be reused (within your program) by using
+undef() and/or delete().
+
+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.
+
+In general, memory allocation and de-allocation isn't something you can
+or should be worrying about much in Perl.
+
+See also "How can I make my Perl program take less memory?"
+
+=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/ .
+
+=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 later in L<perlfaq3>, but the curious might still be able to
+de-compile it. You can try using the native-code compiler described
+later, 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?
+
+(contributed by brian d foy)
+
+In general, you can't do this. There are some things that may work
+for your situation though. People usually ask this question
+because they want to distribute their works without giving away
+the source code, and most solutions trade disk space for convenience.
+You probably won't see much of a speed increase either, since most
+solutions simply bundle a Perl interpreter in the final product
+(but see L<How can I make my Perl program run faster?>).
+
+The Perl Archive Toolkit ( http://par.perl.org/ ) is Perl's
+analog to Java's JAR. It's freely available and on CPAN (
+http://search.cpan.org/dist/PAR/ ).
+
+There are also some commercial products that may work for you, although
+you have to buy a license for them.
+
+The Perl Dev Kit ( http://www.activestate.com/Products/Perl_Dev_Kit/ )
+from ActiveState can "Turn your Perl programs into ready-to-run
+executables for HP-UX, Linux, Solaris and Windows."
+
+Perl2Exe ( http://www.indigostar.com/perl2exe.htm ) is a command line
+program for converting perl scripts to executable files. It targets both
+Windows and Unix platforms.
+
+=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>.
+
+Under "Classic" MacOS, a perl program will have the appropriate Creator and
+Type, so that double-clicking them will invoke the MacPerl application.
+Under Mac OS X, clickable apps can be made from any C<#!> script using Wil
+Sanchez' DropScript utility: http://www.wsanchez.net/software/ .
+
+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 (including Mac OS X)
+ perl -e 'print "Hello world\n"'
+
+ # DOS, etc.
+ perl -e "print \"Hello world\n\""
+
+ # Mac Classic
+ 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.
+
+A good book on OO on Perl is the "Object-Oriented Perl"
+by Damian Conway from Manning Publications, or "Intermediate Perl"
+by Randal Schwartz, brian d foy, and Tom Phoenix from O'Reilly Media.
+
+=head2 Where can I learn about linking C with Perl?
+
+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.
+
+You might not need all the power of XS. The Inline::C module lets
+you put C code directly in your Perl source. It handles all the
+magic to make it work. You still have to learn at least some of
+the perl API but you won't have to deal with the complexity of the
+XS support files.
+
+=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?
+
+(contributed by brian d foy)
+
+The C<ExtUtils::MakeMaker> module, better known simply as "MakeMaker",
+turns a Perl script, typically called C<Makefile.PL>, into a Makefile.
+The Unix tool C<make> uses this file to manage dependencies and actions
+to process and install a Perl distribution.
+
+=head1 AUTHOR AND COPYRIGHT
+
+Copyright (c) 1997-2010 Tom Christiansen, Nathan Torkington, and
+other authors as noted. All rights reserved.
+
+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
+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.