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NAME
perl - Practical Extraction and Report Language
SYNOPSIS
perl [ -sTuU ] [ -hv ] [ -V[:*configvar*] ] [ -cw ] [
-d[:*debugger*] ] [ -D[*number/list*] ] [ -pna ] [ -F*pattern* ]
[ -l[*octal*] ] [ -0[*octal*] ] [ -I*dir* ] [ -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
perl5004delta Perl changes in version 5.004
perlfaq Perl frequently asked questions
perltoc Perl documentation table of contents
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
perlopentut Perl open() tutorial
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
perlreftut Perl references short introduction
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
perlthrtut Perl threads tutorial
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.
DESCRIPTION
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
(sometimes called "associative arrays") grow as necessary to
prevent degraded performance. Perl can use 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:
* 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". Anonymous subroutines exhibit
deep binding of lexical variables (closures).
* 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.
* 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.
* 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 for just autoloading.
* 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.
* 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.
* 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.
AVAILABILITY
Perl is available for the vast majority of operating system
platforms, including most Unix-like platforms. The following
situation is as of February 1999 and Perl 5.005_03.
The following platforms are able to build Perl from the standard
source code distribution available at
http://www.perl.com/CPAN/src/index.html
AIX Linux SCO ODT/OSR
A/UX MachTen Solaris
BeOS MPE/iX SunOS
BSD/OS NetBSD SVR4
DG/UX NextSTEP Tru64 UNIX 3)
DomainOS OpenBSD Ultrix
DOS DJGPP 1) OpenSTEP UNICOS
DYNIX/ptx OS/2 VMS
FreeBSD OS390 2) VOS
HP-UX PowerMAX Windows 3.1 1)
Hurd QNX Windows 95 1) 4)
IRIX Windows 98 1) 4)
Windows NT 1) 4)
1) in DOS mode either the DOS or OS/2 ports can be used
2) formerly known as MVS
3) formerly known as Digital UNIX and before that DEC OSF/1
4) compilers: Borland, Cygwin32, Mingw32 EGCS/GCC, VC++
The following platforms have been known to build Perl from the
source but for the Perl release 5.005_03 we haven't been able to
verify them, either because the hardware/software platforms are
rather rare or because we don't have an active champion on these
platforms, or both.
3b1 FPS Plan 9
AmigaOS GENIX PowerUX
ConvexOS Greenhills RISC/os
CX/UX ISC Stellar
DC/OSx MachTen 68k SVR2
DDE SMES MiNT TI1500
DOS EMX MPC TitanOS
Dynix NEWS-OS UNICOS/mk
EP/IX Opus Unisys Dynix
ESIX Unixware
The following platforms are planned to be supported in the
standard source code distribution of the Perl release 5.006 but
are not supported in the Perl release 5.005_03:
BS2000
Netware
Rhapsody
VM/ESA
The following platforms have their own source code distributions
and binaries available via
http://www.perl.com/CPAN/ports/index.html.
Perl release
AS/400 5.003
MacOS 5.004
Netware 5.003_07
Tandem Guardian 5.004
The following platforms have only binaries available via
http://www.perl.com/CPAN/ports/index.html.
Perl release
Acorn RISCOS 5.005_02
AOS 5.002
LynxOS 5.004_02
ENVIRONMENT
See the perlrun manpage.
AUTHOR
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>.
FILES
"@INC" locations of perl 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. 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?
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 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 251
characters. Line numbers displayed by diagnostics are internally
stored as short integers, so they are limited to a maximum of
65535 (higher numbers usually being affected by wraparound).
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.
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 principal virtues of a programmer are Laziness,
Impatience, and Hubris. See the Camel Book for why.