perl - Practical Extraction and Report Language
perl [ -sTuU ] [ -hv ] [ -V[:configvar] ] [ -cw ] [ -d[:debugger] ] [ -D[number/list] ] [ -pna ] [ -Fpattern ] [ -l[octal] ] [ -0[octal] ] [ -Idir ] [ -m[-]module ] [ -M[-]'module...' ] [ -P ] [ -S ] [ -x[dir] ] [ -i[extension] ] [ -e 'command' ] [ -- ] [ programfile ] [ argument ]...
For ease of access, the Perl manual has been split up into a number of sections:
perl Perl overview (this section)
perldelta Perl changes since previous version
perl5.004delta Perl changes between 5.003 and 5.004
perlfaq Perl frequently asked questions
perldata Perl data structures
perlsyn Perl syntax
perlop Perl operators and precedence
perlre Perl regular expressions
perlrun Perl execution and options
perlfunc Perl builtin functions
perlvar Perl predefined variables
perlsub Perl subroutines
perlmod Perl modules: how they work
perlmodlib Perl modules: how to write and use
perlmodinstall Perl modules: how to install from CPAN
perlform Perl formats
perllocale Perl locale support
perlref Perl references
perldsc Perl data structures intro
perllol Perl data structures: lists of lists
perltoot Perl OO tutorial
perlobj Perl objects
perltie Perl objects hidden behind simple variables
perlbot Perl OO tricks and examples
perlipc Perl interprocess communication
perldebug Perl debugging
perldiag Perl diagnostic messages
perlsec Perl security
perltrap Perl traps for the unwary
perlport Perl portability guide
perlstyle Perl style guide
perlpod Perl plain old documentation
perlbook Perl book information
perlembed Perl ways to embed perl in your C or C++ application
perlapio Perl internal IO abstraction interface
perlxs Perl XS application programming interface
perlxstut Perl XS tutorial
perlguts Perl internal functions for those doing extensions
perlcall Perl calling conventions from C
perlhist Perl history records
(If you're intending to read these straight through for the first time, the suggested order will tend to reduce the number of forward references.)
By default, all of the above manpages are installed in the /usr/local/man/ directory.
Extensive additional documentation for Perl modules is available. The default configuration for perl will place this additional documentation in the /usr/local/lib/perl5/man directory (or else in the man subdirectory of the Perl library directory). Some of this additional documentation is distributed standard with Perl, but you'll also find documentation for third-party modules there.
You should be able to view Perl's documentation with your
man(1) program by including the proper directories in the appropriate start-up files, or in the
MANPATH environment variable. To find out where the configuration has installed the manpages, type:
perl -V:man.dir
If the directories have a common stem, such as /usr/local/man/man1
and /usr/local/man/man3, you need only to add that stem (/usr/local/man) to your
man(1) configuration files or your
MANPATH environment variable. If they do not share a stem, you'll have to add both stems.
If that doesn't work for some reason, you can still use the supplied perldoc script to view module information. You might also look into getting a replacement man program.
If something strange has gone wrong with your program and you're not sure where you should look for help, try the -w switch first. It will often point out exactly where the trouble is.
Perl is a language optimized for scanning arbitrary text files, extracting information from those text files, and printing reports based on that information. It's also a good language for many system management tasks. The language is intended to be practical (easy to use, efficient, complete) rather than beautiful (tiny, elegant, minimal).
Perl combines (in the author's opinion, anyway) some of the best features of C, sed, awk, and sh, so people familiar with those languages should have little difficulty with it. (Language historians will also note some vestiges of csh, Pascal, and even BASIC-PLUS.) Expression syntax corresponds quite closely to C expression syntax. Unlike most Unix utilities, Perl does not arbitrarily limit the size of your data--if you've got the memory, Perl can slurp in your whole file as a single string. Recursion is of unlimited depth. And the tables used by hashes (previously called ``associative arrays'') grow as necessary to prevent degraded performance. Perl uses sophisticated pattern matching techniques to scan large amounts of data very quickly. Although optimized for scanning text, Perl can also deal with binary data, and can make dbm files look like hashes. Setuid Perl scripts are safer than C programs through a dataflow tracing mechanism which prevents many stupid security holes.
If you have a problem that would ordinarily use sed or awk or sh, but it exceeds their capabilities or must run a little faster, and you don't want to write the silly thing in C, then Perl may be for you. There are also translators to turn your sed and awk scripts into Perl scripts.
But wait, there's more...
Perl version 5 is nearly a complete rewrite, and provides the following additional benefits:
It is now possible to write much more readable Perl code (even within regular expressions). Formerly cryptic variable names can be replaced by mnemonic identifiers. Error messages are more informative, and the optional warnings will catch many of the mistakes a novice might make. This cannot be stressed enough. Whenever you get mysterious behavior, try the -w switch!!! Whenever you don't get mysterious behavior, try using -w anyway.
Okay, that's definitely enough hype.
See the perlrun manpage.
Larry Wall <larry@wall.org>, with the help of oodles of other folks.
If your Perl success stories and testimonials may be of help to others who wish to advocate the use of Perl in their applications, or if you wish to simply express your gratitude to Larry and the Perl developers, please write to <perl-thanks@perl.org>.
"/tmp/perl-e$$" temporary file for -e commands "@INC" locations of perl libraries
a2p awk to perl translator
s2p sed to perl translator
The -w switch produces some lovely diagnostics.
See the perldiag manpage for explanations of all Perl's diagnostics. The use
diagnostics pragma automatically turns Perl's normally terse warnings and errors into
these longer forms.
Compilation errors will tell you the line number of the error, with an indication of the next token or token type that was to be examined. (In the case of a script passed to Perl via -e switches, each -e is counted as one line.)
Setuid scripts have additional constraints that can produce error messages such as ``Insecure dependency''. See the perlsec manpage.
Did we mention that you should definitely consider using the -w switch?
The -w switch is not mandatory.
Perl is at the mercy of your machine's definitions of various operations such as type casting,
atof(), and floating-point output with
sprintf().
If your stdio requires a seek or eof between reads and writes on a particular stream, so does Perl. (This doesn't apply to
sysread() and
syswrite().)
While none of the built-in data types have any arbitrary size limits (apart from memory size), there are still a few arbitrary limits: a given variable name may not be longer than 255 characters, and no component of your PATH may be longer than 255 if you use -S. A regular expression may not compile to more than 32767 bytes internally.
You may mail your bug reports (be sure to include full configuration
information as output by the myconfig program in the perl source tree, or
by perl -V) to <perlbug@perl.com>. If you've succeeded in compiling perl, the perlbug script in the
utils/ subdirectory can be used to help mail in a bug report.
Perl actually stands for Pathologically Eclectic Rubbish Lister, but don't tell anyone I said that.
The Perl motto is ``There's more than one way to do it.'' Divining how many more is left as an exercise to the reader.
The three principal virtues of a programmer are Laziness, Impatience, and Hubris. See the Camel Book for why.
If rather than formatting bugs, you encounter substantive content errors in these documents, such as mistakes in the explanations or code, please use the perlbug utility included with the Perl distribution.