PERL(1)PERL(1)NAMEperl - Practical Extraction and Report Language
SYNOPSIS
For ease of access, the Perl manual has been split up into a number of
individual man pages:
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.
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:
· Many usability enhancements
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.
· Simplified grammar
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.
· Lexical scoping
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".
· Arbitrarily nested data structures
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.
· Modularity and reusability
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.
· Object-oriented programming
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.
· Embeddible and Extensible
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.
· POSIX compliant
A major new module is the POSIX module, which provides access to
all available POSIX routines and definitions, via object classes
where appropriate.
· Package constructors and destructors
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.
· Multiple simultaneous DBM implementations
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.
· Subroutine definitions may now be autoloaded
In fact, the AUTOLOAD mechanism also allows you to define any
arbitrary semantics for undefined subroutine calls. It's not just
for autoloading.
· Regular expression enhancements
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
HOME Used if chdir has no argument.
LOGDIR Used if chdir has no argument and HOME is not set.
PATH Used in executing subprocesses, and in finding the script
if -S is used.
PERL5LIB 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.
PERL5DB The command used to get the debugger code. If unset, uses
BEGIN { require 'perl5db.pl' }
PERLLIB 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.
3rd Berkeley DistributionPERL(1)
