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
    perlfaq	Perl Freqently Asked Questions list

    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
    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
    perlstyle	Perl style guide

    perlpod	Perl plain old documentation
    perlbook	Perl book information

    perlembed	Perl how to embed perl in your C or C++ app
    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

(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.)

Additional documentation for Perl modules is available in the /usr/local/man/ directory. Some of this is distributed standard with Perl, but you'll also find third-party modules there. You should be able to view this with your man program by including the proper directories in the appropriate start-up files. To find out where these are, type:

    perl -V:man.dir

If the directories were /usr/local/man/man1 and /usr/local/man/man3, you would need to add only /usr/local/man to your MANPATH. If they are different, 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:

Ok, that's definitely enough hype.


See the perlrun manpage.


Larry Wall <>, with the help of oodles of other folks.


 "/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.

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 sprintf. The latter can even trigger a core dump when passed ludicrous input values.

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 <>. 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.