Objects perlref, perlmod, perlobj, perltie Data Structures perlref, perllol, perldsc Modules perlmod, perlsub Regexps perlre, perlfunc, perlop Moving to perl5 perltrap, perl Linking w/C perlxstut, perlxs, perlcall, perlguts, perlembed Various CPAN/doc/FMTEYEWTK/index.html (not a man-page but still useful)
the perltoc manpage provides a crude table of contents for the perl man page set.
perldebug 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
-w?
Have you tried use strict?
Did you check the returns of each and every system call?
Did you read the perltrap manpage?
Have you tried the Perl debugger, described in the perldebug manpage?
perl -MO=Xref[,OPTIONS] foo.pl
indent
will do for C. The complex feedback between the scanner and the parser
(this feedback is what confuses the vgrind and emacs programs) make it
challenging at best to write a stand-alone Perl parser.
Of course, if you simply follow the guidelines in the perlstyle manpage, you shouldn't need to reformat.
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) codes, and even less programmable editors can provide significant assistance.
If you are using to using vgrind program for printing out nice code to a laser print, you can take a stab at this using CPAN/doc/misc/tips/working.vgrind.entry, but the results are not particularly satisfying for more sophisticated code.
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.
Other approaches include autoloading 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 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 the compiling your Perl programs.
If you're currently linking your perl executable to a shared 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 INSTALL file in the source distribution for more information.
Unsubstantiated reports allege that Perl interpreters that use sfio outperform those that don't (for IO intensive applications). To try this, see the INSTALL file in the source distribution, especially 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 a viable option, as it only worked on a few architectures, and wasn't a good solution anyway.
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 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 built-in malloc. Whichever one it is, try
using the other one and see whether this makes a difference. Information
about malloc is in the INSTALL file in the source distribution. You can find out whether you are using
perl's malloc by typing perl -V:usemymalloc.
sub makeone {
my @a = ( 1 .. 10 );
return \@a;
}
for $i ( 1 .. 10 ) {
push @many, makeone();
}
print $many[4][5], "\n";
print "@many\n";
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 goes
out of scope, so you can't get its space automatically reclaimed, although
undefing and/or deleteing it will achieve the
same effect. In general, memory allocation and de-allocation isn't
something you can or should be worrying about much in Perl, but even this
capability (preallocation of data types) is in the works.
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 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 processes.
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.
First of all, however, you 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.
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 often possible that someone could 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 they might be able to decrypt it. You can try using the byte-code compiler and interpreter described below, but they might be able to de-compile it. You can try using the native-code compiler described below, but they 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 else 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. Your access to it does not give you permission to use it blah blah blah.''
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.
Malcolm will be in charge of the 5.005 release of Perl itself to try to unify and merge his compiler and multithreading work into the main release.
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 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 my system, /usr/bin/perl is only 11k in size!
extproc perl -S -your_switches
as the first line in *.cmd file (-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 ALTERNATIVE_SHEBANG
(see the INSTALL file in the source distribution for more information).
The Win95/NT installation, when using the HIP 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 Type, so that double-clicking them will invoke the perl application.
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 security risk. Take the time to figure out how to do it correctly.
perlrun man page for more information. Some
examples follow. (These assume standard Unix shell quoting rules.)
# sum first and last fields
perl -lane 'print $F[0] + $F[-1]'
# identify text files
perl -le 'for(@ARGV) {print if -f && -T}' *
# remove comments from C program
perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c
# make file a month younger than today, defeating reaper daemons
perl -e '$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 entry. :-)
For example:
# Unix
perl -e 'print "Hello world\n"'
# DOS, etc.
perl -e "print \"Hello world\n\""
# Mac
print "Hello world\n"
(then Run "Myscript" or Shift-Command-R)
# 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:
perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
And don't even try to explain the default command processors -- CMD.EXE in Windows NT slipped a lot of standard Unix functionality in when nobody was looking, but just try to find documentation for its quoting rules.
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.
I'm afraid that there is no general solution to all of this. It is a mess, pure and simple.
[Some of this answer was contributed by Kenneth Albanowski.]
The Idiot's Guide to Solving Perl/CGI Problems, by Tom Christiansen http://www.perl.com/perl/faq/idiots-guide.html
Frequently Asked Questions about CGI Programming, by Nick Kew ftp://rtfm.mit.edu/pub/usenet/news.answers/www/cgi-faq http://www3.pair.com/webthing/docs/cgi/faqs/cgifaq.shtml
Perl/CGI programming FAQ, by Shishir Gundavaram and Tom Christiansen http://www.perl.com/perl/faq/perl-cgi-faq.html
The WWW Security FAQ, by Lincoln Stein http://www-genome.wi.mit.edu/WWW/faqs/www-security-faq.html
World Wide Web FAQ, by Thomas Boutell http://www.boutell.com/faq/
make test TEST_VERBOSE=1 along with perl -V.
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;