=head1 NAME
-perlfaq3 - Programming Tools ($Revision: 1.22 $, $Date: 1997/04/24 22:43:42 $)
+perlfaq3 - Programming Tools ($Revision: 1.22 $, $Date: 2002/05/06 13:11:13 $)
=head1 DESCRIPTION
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:
+Have you read the appropriate manpages? Here's a brief index:
Basics perldata, perlvar, perlsyn, perlop, perlsub
Execution perlrun, perldebug
Objects perlref, perlmod, perlobj, perltie
Data Structures perlref, perllol, perldsc
Modules perlmod, perlmodlib, perlsub
- Regexps perlre, perlfunc, perlop, perllocale
+ Regexes perlre, perlfunc, perlop, perllocale
Moving to perl5 perltrap, perl
Linking w/C perlxstut, perlxs, perlcall, perlguts, perlembed
- Various http://www.perl.com/CPAN/doc/FMTEYEWTK/index.html
- (not a man-page but still useful)
+ Various http://www.cpan.org/misc/olddoc/FMTEYEWTK.tgz
+ (not a man-page but still useful, a collection
+ of various essays on Perl techniques)
-L<perltoc> provides a crude table of contents for the perl man page set.
+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) man page, on an "empty" program, like this:
+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
+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.
+In general, not yet. There is psh available at
+
+ http://www.focusresearch.com/gregor/psh
+
+Which includes the following description:
+
+ The Perl Shell is a shell that combines the interactive nature
+ of a Unix shell with the power of Perl. The goal is to eventually
+ have a full featured shell that behaves as expected for normal
+ shell activity. But, the Perl Shell will use Perl syntax and
+ functionality for control-flow statements and other things.
+
+The Shell.pm module (distributed with Perl) makes Perl try commands
+which aren't part of the Perl language as shell commands. perlsh
+from the source distribution is simplistic and uninteresting, but
+may still be what you want.
=head2 How do I debug my Perl programs?
-Have you used C<-w>?
+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>.
-Have you tried C<use strict>?
+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.
-Did you check the returns of each and every system call?
+ open(FH, "> /etc/cantwrite")
+ or die "Couldn't write to /etc/cantwrite: $!\n";
-Did you read L<perltrap>?
+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>?
+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 CPAN, and also use
-Benchmark.pm from the standard distribution. Benchmark lets you time
-specific portions of your code, while Devel::DProf gives detailed
-breakdowns of where your code spends its time.
+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.
+The B::Xref module can be used to generate cross-reference reports
+for Perl programs.
- perl -MO=Xref[,OPTIONS] foo.pl
+ 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) will
-do 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.
+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 does
+lots of things related to generating nicely printed output of
+documents, as does enscript at http://people.ssh.fi/mtr/genscript/ .
-Of course, if you simply follow the guidelines in L<perlstyle>, you
-shouldn't need to reformat.
+=head2 Is there a ctags for Perl?
-Your editor can and should help you with source formatting. The
-perl-mode for emacs can provide a remarkable amount of help with most
-(but not all) code, and even less programmable editors can provide
-significant assistance.
+Recent versions of ctags do much more than older versions did.
+EXUBERANT CTAGS is available from http://ctags.sourceforge.net/
+and does a good job of making tags files for perl code.
-If you are used to using 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.
+There is also a simple one at
+http://www.cpan.org/authors/id/TOMC/scripts/ptags.gz which may do
+the trick. It can be easy to hack this into what you want.
-=head2 Is there a ctags for Perl?
+=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:
+
+=over 4
+
+=item Komodo
+
+ActiveState's cross-platform (as of April 2001 Windows and Linux),
+multi-language IDE has Perl support, including a regular expression
+debugger and remote debugging
+( http://www.ActiveState.com/Products/Komodo/index.html ). (Visual
+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, apparently for any platform
+that runs Perl.
+
+=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 PerlBuilder
+
+( http://www.solutionsoft.com/perl.htm ) is an integrated development
+environment for Windows that supports Perl development.
+
+=item visiPerl+
+
+( http://helpconsulting.net/visiperl/ )
+From Help Consulting, for Windows.
+
+=item OptiPerl
+
+( http://www.optiperl.com/ ) is a Windows IDE with simulated CGI
+environment, including debugger and syntax highlighting editor.
+
+=back
+
+For Windows there's also the
+
+=over 4
+
+=item CodeMagicCD
+
+( http://www.codemagiccd.com/ ) Collection of various programming
+tools for Windows: Perl (5.005_03), TclTk, Python, GNU programming
+tools, REBOL, wxWindows toolkit, the MinGW GNU C/C++ compiler, DJGPP
+GNU C/C++ compiler, Cint C interpreter, YaBasic.
+
+=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 Mac OS, the same concerns apply. MacPerl
+(for Classic environments) comes with a simple editor.
+Popular external editors are BBEdit ( http://www.bbedit.com/ )
+or Alpha ( http://www.kelehers.org/alpha/ ). Mac OS X users can
+use Unix editors as well.
+
+=over 4
+
+=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
+
+There is also a toyedit Text widget based editor written in Perl
+that is distributed with the Tk module on CPAN. The ptkdb
+( http://world.std.com/~aep/ptkdb/ ) is a Perl/tk based debugger that
+acts as a development environment of sorts. Perl Composer
+( http://perlcomposer.sourceforge.net/vperl.html ) is an IDE for Perl/Tk
+GUI creation.
+
+In addition to an editor/IDE you might be interested in a more
+powerful shell environment for Win32. Your options include
+
+=over 4
-There's a simple one at
-http://www.perl.com/CPAN/authors/id/TOMC/scripts/ptags.gz which may do
-the trick.
+=item Bash
+
+from the Cygwin package ( http://sources.redhat.com/cygwin/ )
+
+=item Ksh
+
+from the MKS Toolkit ( http://www.mks.com/ ), or the Bourne shell of
+the U/WIN environment ( http://www.research.att.com/sw/tools/uwin/ )
+
+=item Tcsh
+
+ftp://ftp.astron.com/pub/tcsh/ , see also
+http://www.primate.wisc.edu/software/csh-tcsh-book/
+
+=item Zsh
+
+ftp://ftp.blarg.net/users/amol/zsh/ , see also http://www.zsh.org/
+
+=back
+
+MKS and U/WIN are commercial (U/WIN is free for educational and
+research purposes), Cygwin is covered by the GNU 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 BBEdit and BBEdit Lite
+
+are text editors for Mac OS that have a Perl sensitivity mode
+( http://web.barebones.com/ ).
+
+=item Alpha
+
+is an editor, written and extensible in Tcl, that nonetheless has
+built in support for several popular markup and programming languages
+including Perl and HTML ( http://alpha.olm.net/ ).
+
+=back
+
+Pepper and Pe are programming language sensitive text editors for Mac
+OS X and BeOS respectively ( http://www.hekkelman.com/ ).
=head2 Where can I get Perl macros for vi?
For a complete version of Tom Christiansen's vi configuration file,
-see http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc,
-the standard benchmark file for vi emulators. This runs best with nvi,
+see http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz ,
+the standard benchmark file for vi emulators. The file runs best with nvi,
the current version of vi out of Berkeley, which incidentally can be built
-with an embedded Perl interpreter -- see http://www.perl.com/CPAN/src/misc.
+with an embedded Perl interpreter--see http://www.cpan.org/src/misc/ .
=head2 Where can I get perl-mode for emacs?
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
+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",
+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 "main'foo"
-(single quote), and mess up the indentation and hilighting. You
-should be using "main::foo", anyway.
+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.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep;
+directory http://www.cpan.org/authors/Tom_Christiansen/scripts/rep ;
this program repeats a command and updates the screen as needed, rendering
B<rep ps axu> similar to B<top>.
Tk is a completely Perl-based, object-oriented interface to the Tk toolkit
that doesn't force you to use Tcl just to get at Tk. Sx is an interface
to the Athena Widget set. Both are available from CPAN. See the
-directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/
+directory http://www.cpan.org/modules/by-category/08_User_Interfaces/
+
+Invaluable for Perl/Tk programming are the Perl/Tk FAQ at
+http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference
+Guide available at
+http://www.cpan.org/authors/Stephen_O_Lidie/ , and the
+online manpages at
+http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html .
=head2 How can I generate simple menus without using CGI or Tk?
-The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
+The http://www.cpan.org/authors/id/SKUNZ/perlmenu.v4.0.tar.gz
module, which is curses-based, can help with this.
-=head2 What is undump?
-
-See the next questions.
-
=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. Chapter 8 in the Camel
-has some efficiency tips in it you might want to look at.
-
-Other approaches include autoloading seldom-used Perl code. See the
+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
+``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 is the use of
-modules that have critical sections written in C (for instance, the
+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).
In some cases, it may be worth it to use the backend compiler to
produce byte code (saving compilation time) or compile into C, which
will certainly save compilation time and sometimes a small amount (but
not much) execution time. See the question about compiling your Perl
-programs.
+programs for more on the compiler--the wins aren't as obvious as you'd
+hope.
-If you're currently linking your perl executable to a shared libc.so,
+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
information.
Unsubstantiated reports allege that Perl interpreters that use sfio
-outperform those that don't (for IO intensive applications). To try
+outperform those that don't (for I/O intensive applications). To try
this, see the F<INSTALL> file in the source distribution, especially
-the "Selecting File IO mechanisms" section.
+the ``Selecting File I/O mechanisms'' section.
The undump program was an old attempt to speed up your Perl program
by storing the already-compiled form to disk. This is no longer
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 that, and hashes use even more. While
+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 for a considerable memory savings. The standard
+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
distribution. You can find out whether you are using perl's malloc by
typing C<perl -V:usemymalloc>.
+Of course, the best way to save memory is to not do anything to waste
+it in the first place. Good programming practices can go a long way
+toward this:
+
+=over 4
+
+=item * Don't slurp!
+
+Don't read an entire file into memory if you can process it line
+by line. Or more concretely, use a loop like this:
+
+ #
+ # Good Idea
+ #
+ while (<FILE>) {
+ # ...
+ }
+
+instead of this:
+
+ #
+ # Bad Idea
+ #
+ @data = <FILE>;
+ foreach (@data) {
+ # ...
+ }
+
+When the files you're processing are small, it doesn't much matter which
+way you do it, but it makes a huge difference when they start getting
+larger.
+
+=item * Use map and grep selectively
+
+Remember that both map and grep expect a LIST argument, so doing this:
+
+ @wanted = grep {/pattern/} <FILE>;
+
+will cause the entire file to be slurped. For large files, it's better
+to loop:
+
+ while (<FILE>) {
+ push(@wanted, $_) if /pattern/;
+ }
+
+=item * Avoid unnecessary quotes and stringification
+
+Don't quote large strings unless absolutely necessary:
+
+ my $copy = "$large_string";
+
+makes 2 copies of $large_string (one for $copy and another for the
+quotes), whereas
+
+ my $copy = $large_string;
+
+only makes one copy.
+
+Ditto for stringifying large arrays:
+
+ {
+ local $, = "\n";
+ print @big_array;
+ }
+
+is much more memory-efficient than either
+
+ print join "\n", @big_array;
+
+or
+
+ {
+ local $" = "\n";
+ print "@big_array";
+ }
+
+
+=item * Pass by reference
+
+Pass arrays and hashes by reference, not by value. For one thing, it's
+the only way to pass multiple lists or hashes (or both) in a single
+call/return. It also avoids creating a copy of all the contents. This
+requires some judgment, however, because any changes will be propagated
+back to the original data. If you really want to mangle (er, modify) a
+copy, you'll have to sacrifice the memory needed to make one.
+
+=item * Tie large variables to disk.
+
+For "big" data stores (i.e. ones that exceed available memory) consider
+using one of the DB modules to store it on disk instead of in RAM. This
+will incur a penalty in access time, but that's probably better than
+causing your hard disk to thrash due to massive swapping.
+
+=back
+
=head2 Is it unsafe to return a pointer to local data?
No, Perl's garbage collection system takes care of this.
=head2 How can I free an array or hash so my program shrinks?
-You can't. Memory the system allocates to a program will in practice
-never be returned to the system. That's why long-running programs
-sometimes re-exec themselves.
+You usually can't. On most operating systems, memory
+allocated to a program can never be returned to the system.
+That's why long-running programs sometimes re-exec
+themselves. Some operating systems (notably, systems that
+use mmap(2) for allocating large chunks of memory) can
+reclaim memory that is no longer used, but on such systems,
+perl must be configured and compiled to use the OS's malloc,
+not perl's.
However, judicious use of my() on your variables will help make sure
-that they go out of scope so that Perl can free up their storage for
-use in other parts of your program. (NB: my() variables also execute
-about 10% faster than globals.) A global variable, of course, never
+that they go out of scope so that Perl can free up that space for
+use in other parts of your program. A global variable, of course, never
goes out of scope, so you can't get its space automatically reclaimed,
although undef()ing and/or delete()ing it will achieve the same effect.
In general, memory allocation and de-allocation isn't something you can
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 at least 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::* modules (from CPAN),
-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. With the FCGI module (from CPAN), a Perl
-executable compiled with sfio (see the F<INSTALL> file in the
-distribution) and the mod_fastcgi module (available from
-http://www.fastcgi.com/) each of your perl scripts becomes a permanent
-CGI daemon process.
+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 scripts, so investigate them with
+and on the way you write your CGI programs, so investigate them with
care.
-See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/.
+See http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
+
+A non-free, commercial product, ``The Velocity Engine for Perl'',
+(http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ )
+might also be worth looking at. It will allow you to increase the
+performance of your Perl programs, running programs up to 25 times
+faster than normal CGI Perl when running in persistent Perl mode or 4
+to 5 times faster without any modification to your existing CGI
+programs. Fully functional evaluation copies are available from the
+web site.
=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".
+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.) So you have to leave the
-permissions at the socially friendly 0755 level.
+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
+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 (Filter::* from CPAN).
-But crackers might be able to decrypt it. You can try using the byte
-code compiler and interpreter described below, but crackers might be
-able to de-compile it. You can try using the native-code compiler
-described below, 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 (this is true of every
-language, not just Perl).
+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 below, but the curious might still be able to de-compile it.
+You can try using the native-code compiler described below, 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).
If you're concerned about people profiting from your code, then the
-bottom line is that nothing but a restrictive licence will give you
+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.
+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 licence's wording will stand up in court.
+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?
Malcolm Beattie has written a multifunction backend compiler,
-available from CPAN, that can do both these things. It is as of
-Feb-1997 in late alpha release, which means it's fun to play with if
-you're a programmer but not really for people looking for turn-key
-solutions.
-
-I<Please> understand that merely compiling into C does not in and of
-itself guarantee that your code will run very much faster. That's
-because except for lucky cases where a lot of native type inferencing
-is possible, the normal Perl run time system is still present and thus
-will still take just as long to run and be just as big. Most programs
-save little more than compilation time, leaving execution no more than
-10-30% faster. A few rare programs actually benefit significantly
-(like several times faster), but this takes some tweaking of your
-code.
-
-The 5.005 release of Perl itself, whose main goal is merging the various
-non-Unix ports back into the one Perl source, will also have preliminary
-(strictly beta) support for Malcolm's compiler and his light-weight
-processes (sometimes called "threads").
+available from CPAN, that can do both these things. It is included
+in the perl5.005 release, but is still considered experimental.
+This means it's fun to play with if you're a programmer but not
+really for people looking for turn-key solutions.
+
+Merely compiling into C does not in and of itself guarantee that your
+code will run very much faster. That's because except for lucky cases
+where a lot of native type inferencing is possible, the normal Perl
+run-time system is still present and so your program will take just as
+long to run and be just as big. Most programs save little more than
+compilation time, leaving execution no more than 10-30% faster. A few
+rare programs actually benefit significantly (even running several times
+faster), but this takes some tweaking of your code.
You'll probably be astonished to learn that the current version of the
compiler generates a compiled form of your script whose executable is
just as big as the original perl executable, and then some. That's
because as currently written, all programs are prepared for a full
eval() statement. You can tremendously reduce this cost by building a
-shared libperl.so library and linking against that. See the
-F<INSTALL> podfile in the perl source distribution for details. If
-you link your main perl binary with this, it will make it miniscule.
-For example, on one author's system, /usr/bin/perl is only 11k in
+shared I<libperl.so> library and linking against that. See the
+F<INSTALL> podfile in the Perl source distribution for details. If
+you link your main perl binary with this, it will make it minuscule.
+For example, on one author's system, F</usr/bin/perl> is only 11k in
size!
In general, the compiler will do nothing to make a Perl program smaller,
-faster, more portable, or more secure. In fact, it will usually hurt
-all of those. The executable will be bigger, your VM system may take
+faster, more portable, or more secure. In fact, it can make your
+situation worse. The executable will be bigger, your VM system may take
longer to load the whole thing, the binary is fragile and hard to fix,
and compilation never stopped software piracy in the form of crackers,
viruses, or bootleggers. The real advantage of the compiler is merely
packaging, and once you see the size of what it makes (well, unless
you use a shared I<libperl.so>), you'll probably want a complete
-Perl install anywayt.
+Perl install anyway.
+
+=head2 How can I compile Perl into Java?
+
+You can also integrate Java and Perl with the
+Perl Resource Kit from O'Reilly and Associates. See
+http://www.oreilly.com/catalog/prkunix/ .
-=head2 How can I get '#!perl' to work on [MS-DOS,NT,...]?
+Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in
+development, allows Perl code to be called from Java. See jpl/README
+in the Perl source tree.
+
+=head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
For OS/2 just use
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<ALTERNATIVE_SHEBANG> (see the
+batch file and codify it in C<ALTERNATIVE_SHEBANG> (see the
F<INSTALL> file in the source distribution for more information).
-The Win95/NT installation, when using the Activeware port of Perl,
-will modify the Registry to associate the .pl extension with the perl
-interpreter. If you install another port, or (eventually) build your
-own Win95/NT Perl using WinGCC, then you'll have to modify the
-Registry yourself.
+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>.
-Macintosh perl scripts will have the the appropriate Creator and
-Type, so that double-clicking them will invoke the perl application.
+Macintosh Perl programs will have the appropriate Creator and
+Type, so that double-clicking them will invoke the Perl application.
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 scripts working for a web server. This is an EXTREMELY big
+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?
+=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.)
echo $PATH | perl -nl -072 -e '
s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'
-Ok, the last one was actually an obfuscated perl entry. :-)
+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?
+=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
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 this is reliable: it depends on the command
-interpreter. Under Unix, the first two often work. Under DOS, it's
-entirely possible neither works. If 4DOS was the command shell, I'd
-probably have better luck like this:
+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>""
quoting variants, except that it makes free use of the Mac's non-ASCII
characters as control characters.
-I'm afraid that there is no general solution to all of this. It is a
-mess, pure and simple.
+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.]
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 these sources:
-
- WWW Security FAQ
- http://www.w3.org/Security/Faq/
-
- Web FAQ
- http://www.boutell.com/faq/
-
- CGI FAQ
- http://www.webthing.com/page.cgi/cgifaq
-
- HTTP Spec
- http://www.w3.org/pub/WWW/Protocols/HTTP/
-
- HTML Spec
- http://www.w3.org/TR/REC-html40/
- http://www.w3.org/pub/WWW/MarkUp/
-
- CGI Spec
- http://www.w3.org/CGI/
-
- CGI Security FAQ
- http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt
+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?
-L<perltoot> is a good place to start, and you can use L<perlobj> and
-L<perlbot> for reference. Perltoot didn't come out until the 5.004
-release, but you can get a copy (in pod, html, or postscript) from
-http://www.perl.com/CPAN/doc/FMTEYEWTK/ .
+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.
+(If you are using really old Perl, you may not have all of these,
+try http://www.perldoc.com/ , but consider upgrading your perl.)
+
+A good book on OO on Perl is the "Object-Oriented Perl"
+by Damian Conway from Manning Publications,
+http://www.manning.com/Conway/index.html
=head2 Where can I learn about linking C with Perl? [h2xs, xsubpp]
solved their problems.
=head2 I've read perlembed, perlguts, etc., but I can't embed perl in
-my C program, what am I doing wrong?
+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 bugreport with the output of
+fail, see L<perlbug> and send a bug report with the output of
C<make test TEST_VERBOSE=1> along with C<perl -V>.
-=head2 When I tried to run my script, I got this message. What does it
-mean?
+=head2 When I tried to run my script, I got this message. What does it mean?
-L<perldiag> has a complete list of perl's error messages and warnings,
-with explanatory text. You can also use the splain program (distributed
-with perl) to explain the error messages:
+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
=head2 What's MakeMaker?
-This module (part of the standard perl distribution) is designed to
+This module (part of the standard Perl distribution) is designed to
write a Makefile for an extension module from a Makefile.PL. For more
information, see L<ExtUtils::MakeMaker>.
=head1 AUTHOR AND COPYRIGHT
-Copyright (c) 1997, 1998 Tom Christiansen and Nathan Torkington.
+Copyright (c) 1997-2002 Tom Christiansen and Nathan Torkington.
All rights reserved.
-When included as part of the Standard Version of Perl, or as part of
-its complete documentation whether printed or otherwise, this work
-may be distributed only under the terms of Perl's Artistic License.
-Any distribution of this file or derivatives thereof I<outside>
-of that package require that special arrangements be made with
-copyright holder.
-
-Irrespective of its distribution, all code examples in this file
-are hereby placed into the public domain. You are permitted and
-encouraged to use this code in your own programs for fun
-or for profit as you see fit. A simple comment in the code giving
-credit would be courteous but is not required.
+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.
https://perl5.git.perl.org / perl5.git / blobdiff