PERL(1)

NAME
perl - Practical Extraction and Report Language

SYNOPSIS
For ease of access, the Perl manual has been split up into a number of sections:

    perl        Perl overview (this section)
    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
    perlref     Perl references and nested data structures
    perlobj     Perl objects
    perlbot     Perl OO tricks and examples
    perldebug   Perl debugging
    perldiag    Perl diagnostic messages
    perlform    Perl formats
    perlipc     Perl interprocess communication
    perlsec     Perl security
    perltrap    Perl traps for the unwary
    perlstyle   Perl style guide
    perlapi     Perl application programming interface
    perlguts    Perl internal functions for those doing extensions
    perlcall    Perl calling conventions from C
    perlovl     Perl overloading semantics
    perlembed   Perl how to embed perl in your C or C++ app
    perlpod     Perl plain old documentation
    perlbook    Perl book information
(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/lib/perl5/man/man3 directory. You can view this with a man(1) program by including the following in the appropriate start-up files. (You may have to adjust the path to match $Config{'man3dir'}.)

    .profile (for sh, bash or ksh users):
        MANPATH=$MANPATH:/usr/local/lib/perl5/man
        export MANPATH
    .login (for csh or tcsh users):
        setenv MANPATH $MANPATH:/usr/local/lib/perl5/man
If that doesn't work for some reason, you can still use the supplied perldoc script to view module information.

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.

DESCRIPTION
Perl is an interpreted 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). It 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 hash tables used by 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 associative arrays (where dbm is available). 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. The new yacc grammar is one half the size of the old one. Many of the arbitrary grammar rules have been regularized. The number of reserved words has been cut by 2/3. Despite this, nearly all old Perl scripts will continue to work unchanged. Perl variables may now be declared within a lexical scope, like "auto" variables in C. Not only is this more efficient, but it contributes to better privacy for "programming in the large". Any scalar value, including any array element, may now contain a reference to any other variable or subroutine. You can easily create anonymous variables and subroutines. Perl manages your reference counts for you. The Perl library is now defined in terms of modules which can be easily shared among various packages. A package may choose to import all or a portion of a module's published interface. Pragmas (that is, compiler directives) are defined and used by the same mechanism. A package can function as a class. Dynamic multiple inheritance and virtual methods are supported in a straightforward manner and with very little new syntax. Filehandles may now be treated as objects. Perl may now be embedded easily in your C or C++ application, and can either call or be called by your routines through a documented interface. The XS preprocessor is provided to make it easy to glue your C or C++ routines into Perl. Dynamic loading of modules is supported. A major new module is the POSIX module, which provides access to all available POSIX routines and definitions, via object classes where appropriate. The new BEGIN and END blocks provide means to capture control as a package is being compiled, and after the program exits. As a degenerate case they work just like awk's BEGIN and END when you use the -p or -n switches. A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB files from the same script simultaneously. In fact, the old dbmopen interface has been generalized to allow any variable to be tied to an object class which defines its access methods. In fact, the AUTOLOAD mechanism also allows you to define any arbitrary semantics for undefined subroutine calls. It's not just for autoloading. You can now specify non-greedy quantifiers. You can now do grouping without creating a backreference. You can now write regular expressions with embedded whitespace and comments for readability. A consistent extensibility mechanism has been added that is upwardly compatible with all old regular expressions.

Ok, that's definitely enough hype.

ENVIRONMENT
Used if chdir has no argument. Used if chdir has no argument and HOME is not set. Used in executing subprocesses, and in finding the script if -S is used. A colon-separated list of directories in which to look for Perl library files before looking in the standard library and the current directory. If PERL5LIB is not defined, PERLLIB is used. The command used to get the debugger code. If unset, uses

        BEGIN { require 'perl5db.pl' }
A colon-separated list of directories in which to look for Perl library files before looking in the standard library and the current directory. If PERL5LIB is defined, PERLLIB is not used.

Apart from these, Perl uses no other environment variables, except to make them available to the script being executed, and to child processes. However, scripts running setuid would do well to execute the following lines before doing anything else, just to keep people honest:

    $ENV{'PATH'} = '/bin:/usr/bin';    # or whatever you need
    $ENV{'SHELL'} = '/bin/sh' if defined $ENV{'SHELL'};
    $ENV{'IFS'} = ''          if defined $ENV{'IFS'};

AUTHOR
Larry Wall <lwall@netlabs.com., with the help of oodles of other folks.

FILES

 "/tmp/perl-e$$"        temporary file for -e commands
 "@INC"                 locations of perl 5 libraries

SEE ALSO

 a2p    awk to perl translator
 s2p    sed to perl translator

DIAGNOSTICS
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?

BUGS
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().

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 identifier 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.

Perl actually stands for Pathologically Eclectic Rubbish Lister, but don't tell anyone I said that.

NOTES
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 principle virtues of a programmer are Laziness, Impatience, and Hubris. See the Camel Book for why.