PERL(1)
NNAAMMEE
perl - Practical Extraction and Report Language
SSYYNNOOPPSSIISS
ppeerrll [ --ssTTuuUU ] [ --hhvv ] [ --VV[:configvar] ]
[ --ccww ] [ --dd[:debugger] ] [ --DD[number/list] ]
[ --ppnnaa ] [ --FFpattern ] [ --ll[octal] ] [ --00[octal] ]
[ --IIdir ] [ --mm[--]module ] [ --MM[--]'module...' ]
[ --PP ] [ --SS ] [ --xx[dir] ]
[ --ii[extension] ]
[ --ee '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 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
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 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
(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 --ww
switch first. It will often point out exactly where the
trouble is.
DDEESSCCRRIIPPTTIIOONN
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, sseedd, aawwkk, and sshh, so people
familiar with those languages should have little
difficulty with it. (Language historians will also note
some vestiges of ccsshh, 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 sseedd or aawwkk
or sshh, 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 sseedd and aawwkk scripts into Perl
scripts.
But wait, there's more...
Perl version 5 is nearly a complete rewrite, and provides
the following additional benefits:
+o 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 --ww switch!!! Whenever you don't
get mysterious behavior, try using --ww anyway.
+o 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.
+o 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". Anonymous
subroutines exhibit deep binding of lexical variables
(closures).
+o 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.
+o 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.
+o 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.
+o Embeddable 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, and Perl itself can be made
into a dynamic library.
+o 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.
+o 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 --pp or --nn
switches.
+o 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.
+o 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 for just autoloading.
+o Regular expression enhancements
You can now specify nongreedy 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.
+o Innumerable Unbundled Modules
The Comprehensive Perl Archive Network described in
the perlmodlib manpage contains hundreds of plug-and-
play modules full of reusable code. See
http://www.perl.com/CPAN for a site near you.
+o Compilability
While not yet in full production mode, a working
perl-to-C compiler does exist. It can generate
portable byte code, simple C, or optimized C code.
Okay, that's definitely enough hype.
EENNVVIIRROONNMMEENNTT
See the perlrun manpage.
AAUUTTHHOORR
Larry Wall lt;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 lt;perl-thanks@perl.org.
FFIILLEESS
"/tmp/perl-e$$" temporary file for -e commands
"@INC" locations of perl libraries
SSEEEE AALLSSOO
a2p awk to perl translator
s2p sed to perl translator
DDIIAAGGNNOOSSTTIICCSS
The --ww 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 --ee switches, each --ee 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 --ww switch?
BBUUGGSS
The --ww 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 --SS. 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
lt;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.
NNOOTTEESS
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.