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diff --git a/Master/tlpkg/tlperl/lib/pods/perlfaq3.pod b/Master/tlpkg/tlperl/lib/pods/perlfaq3.pod new file mode 100755 index 00000000000..2fa78fc6545 --- /dev/null +++ b/Master/tlpkg/tlperl/lib/pods/perlfaq3.pod @@ -0,0 +1,1104 @@ +=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 +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 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://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. + +=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 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; + + my $inst = ExtUtils::Installed->new(); + my @modules = $inst->modules(); + +If you want a list of all of the Perl module filenames, you +can use 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 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 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? + +(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 <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 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? + +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 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 the the 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 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 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 REVISION + +Revision: $Revision$ + +Date: $Date$ + +See L<perlfaq> for source control details and availability. + +=head1 AUTHOR AND COPYRIGHT + +Copyright (c) 1997-2009 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. |