=head1 NAME
-perlfaq3 - Programming Tools ($Revision: 1.27 $, $Date: 1998/07/05 15:07:20 $)
+perlfaq3 - Programming Tools ($Revision: 1.33 $, $Date: 1998/12/29 20:12:12 $)
=head1 DESCRIPTION
=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) man page, on an ``empty'' program, like this:
perl -de 42
Now just type in any legal Perl code, and it will be immediately
evaluated. You can also examine the symbol table, get stack
backtraces, check variable values, set breakpoints, and other
-operations typically found in symbolic debuggers
+operations typically found in symbolic debuggers.
=head2 Is there a Perl shell?
=head2 How do I debug my Perl programs?
-Have you used C<-w>?
+Have you used C<-w>? It enables warnings for dubious practices.
-Have you tried C<use strict>?
+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> or C<use vars>.
-Did you check the returns of each and every system call?
+Did you check the returns of each and every system call? The operating
+system (and thus Perl) tells you whether they worked or not, and if not
+why.
-Did you read L<perltrap>?
+ open(FH, "> /etc/cantwrite")
+ or die "Couldn't write to /etc/cantwrite: $!\n";
-Have you tried the Perl debugger, described in L<perldebug>?
+Did you read L<perltrap>? It's full of gotchas for old and new Perl
+programmers, and even has sections for those of you who are upgrading
+from languages like I<awk> and I<C>.
+
+Have you tried the Perl debugger, described in L<perldebug>? You can
+step through your program and see what it's doing and thus work out
+why what it's doing isn't what it should be doing.
=head2 How do I profile my Perl programs?
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 really proves little about 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
=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
+There is no program that will reformat Perl as much as indent(1) does
+for C. The complex feedback between the scanner and the parser (this
+feedback is what confuses the vgrind and emacs programs) makes it
challenging at best to write a stand-alone Perl parser.
Of course, if you simply follow the guidelines in L<perlstyle>, you
-shouldn't need to reformat.
-
-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.
-
-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
+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 for emacs can provide a remarkable amount of
+help with most (but not all) code, and even less programmable editors
+can provide significant assistance. Tom swears by the following
+settings in vi and its clones:
+
+ set ai sw=4
+ map ^O {^M}^[O^T
+
+Now put that in your F<.exrc> file (replacing the caret characters
+with control characters) and away you go. In insert mode, ^T is
+for indenting, ^D is for undenting, and ^O is for blockdenting --
+as it were. If you haven't used the last one, you're missing
+a lot. A more complete example, with comments, can be found at
+http://www.perl.com/CPAN-local/authors/id/TOMC/scripts/toms.exrc.gz
+
+If you are used to using the I<vgrind> program for printing out nice code
+to a laser printer, you can take a stab at this using
http://www.perl.com/CPAN/doc/misc/tips/working.vgrind.entry, but the
results are not particularly satisfying for sophisticated code.
-=head2 Is there a ctags for Perl?
+The a2ps at http://www.infres.enst.fr/~demaille/a2ps/ does lots of things
+related to generating nicely printed output of documents.
+
+=head2 Is there a etags/ctags for perl?
+
+With respect to the source code for the Perl interpreter, yes.
+There has been support for etags in the source for a long time.
+Ctags was introduced in v5.005_54 (and probably 5.005_03).
+After building perl, type 'make etags' or 'make ctags' and both
+sets of tag files will be built.
-There's a simple one at
+Now, if you're looking to build a tag file for perl code, then there's
+a simple one at
http://www.perl.com/CPAN/authors/id/TOMC/scripts/ptags.gz which may do
-the trick.
+the trick. And if not, it's easy to hack into what you want.
+
+=head2 Is there an IDE or Windows Perl Editor?
+
+If you're on Unix, you already have an IDE -- Unix itself.
+You just have to learn the toolbox. If you're not, then you
+probably don't have a toolbox, so may need something else.
+
+PerlBuilder (XXX URL to follow) is an integrated development
+environment for Windows that supports Perl development. Perl programs
+are just plain text, though, so you could download emacs for Windows
+(XXX) or vim for win32 (http://www.cs.vu.nl/~tmgil/vi.html). If
+you're transferring Windows files to Unix, be sure to transfer in
+ASCII mode so the ends of lines are appropriately converted.
=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,
+see http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc.gz,
the standard benchmark file for vi emulators. This 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.
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"
+Note that the perl-mode of emacs will have fits with C<"main'foo">
(single quote), and mess up the indentation and hilighting. You
-should be using "main::foo", anyway.
+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?
to the Athena Widget set. Both are available from CPAN. See the
directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/
+Invaluable for Perl/Tk programming are: the Perl/Tk FAQ at
+http://w4.lns.cornell.edu/~pvhp/ptk/ptkTOC.html , the Perl/Tk Reference
+Guide available at
+http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ , and the
+online manpages at
+http://www-users.cs.umn.edu/~amundson/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
=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.
+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. 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.
-Other approaches include autoloading seldom-used Perl code. See the
+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
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
Unsubstantiated reports allege that Perl interpreters that use sfio
outperform those that don't (for IO intensive applications). To try
this, see the F<INSTALL> file in the source distribution, especially
-the "Selecting File IO mechanisms" section.
+the ``Selecting File IO 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.
You 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, FreeBSD)
-allegedly reclaim large chunks of memory that is no longer used, but
-it doesn't appear to happen with Perl (yet). The Mac appears to be the
-only platform that will reliably (albeit, slowly) return memory to the OS.
+sometimes re-exec themselves. Some operating systems (notably,
+FreeBSD and Linux) allegedly reclaim large chunks of memory that is no
+longer used, but it doesn't appear to happen with Perl (yet). The Mac
+appears to be the only platform that will reliably (albeit, slowly)
+return memory to the OS.
+
+We've had reports that on Linux (Redhat 5.1) on Intel, C<undef
+$scalar> will return memory to the system, while on Solaris 2.6 it
+won't. In general, try it yourself and see.
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
+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
+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::* 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.
+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
+scripts 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
care.
-See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/.
+See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .
-A non-free, commerical product, 'The Velocity Engine for Perl',
-(http://www.binevolve.com/ or http://www.binevolve.com/bine/vep) might
+A non-free, commercial product, ``The Velocity Engine for Perl'',
+(http://www.binevolve.com/ or
also be worth looking at. It will allow you to increase the performance
-of your perl scripts, upto 25 times faster than normal cgi perl by
+of your perl scripts, upto 25 times faster than normal CGI perl by
running in persistent perl mode, or 4 to 5 times faster without any
-modification to your existing cgi scripts. Fully functional evaluation
+modification to your existing CGI scripts. 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
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
+You can try using encryption via source filters (Filter::* from CPAN),
+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 (this is 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
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
+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.
=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 (like 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
+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 miniscule.
-For example, on one author's system, /usr/bin/perl is only 11k in
+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,
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't. Not yet, anyway. You can integrate Java and Perl with the
+Perl Resource Kit from O'Reilly and Associates. See
+http://www.oreilly.com/catalog/prkunix/ for more information.
+The Java interface will be supported in the core 5.006 release
+of Perl.
-=head2 How can I get '#!perl' to work on [MS-DOS,NT,...]?
+=head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?
For OS/2 just use
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.
-
-Macintosh perl scripts will have the the appropriate Creator and
+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 (Gurusamy Sarathy's is
+the recommended Win95/NT port), or (eventually) build your own
+Win95/NT Perl using a Windows port of gcc (e.g., with cygwin32 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 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
# 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 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,
+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, pure and
+simple. Sucks to be away from Unix, huh? :-)
[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:
+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/
http://www.boutell.com/faq/
CGI FAQ
- http://www.webthing.com/page.cgi/cgifaq
+ http://www.webthing.com/tutorials/cgifaq.html
HTTP Spec
http://www.w3.org/pub/WWW/Protocols/HTTP/
CGI Security FAQ
http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt
+Also take a look at L<perlfaq9>
=head2 Where can I learn about object-oriented Perl programming?
=head1 AUTHOR AND COPYRIGHT
-Copyright (c) 1997, 1998 Tom Christiansen and Nathan Torkington.
+Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington.
All rights reserved.
When included as an integrated part of the Standard Distribution
-of Perl or of its documentation (printed or otherwise), this works is
+of Perl or of its documentation (printed or otherwise), this work is
covered under Perl's Artistic Licence. For separate distributions of
all or part of this FAQ outside of that, see L<perlfaq>.
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.
+
projects / p5sagit/p5-mst-13.2.git / blobdiff