perlfaq1.pod

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For others, it serves as a convenient, high-level replacement for most of
what they'd program in low-level languages like C or C++.  It's ultimately
up to you (and possibly your management) which tasks you'll use Perl
for and which you won't.

If you have a library that provides an API, you can make any component
of it available as just another Perl function or variable using a Perl
extension written in C or C++ and dynamically linked into your main
perl interpreter.  You can also go the other direction, and write your
main program in C or C++, and then link in some Perl code on the fly,
to create a powerful application.  See L<perlembed>.

That said, there will always be small, focused, special-purpose
languages dedicated to a specific problem domain that are simply more
convenient for certain kinds of problems.  Perl tries to be all things
to all people, but nothing special to anyone.  Examples of specialized
languages that come to mind include prolog and matlab.

=head2 When shouldn't I program in Perl?

When your manager forbids it--but do consider replacing them :-).

Actually, one good reason is when you already have an existing
application written in another language that's all done (and done
well), or you have an application language specifically designed for a
certain task (e.g. prolog, make).

For various reasons, Perl is probably not well-suited for real-time
embedded systems, low-level operating systems development work like
device drivers or context-switching code, complex multi-threaded
shared-memory applications, or extremely large applications.  You'll
notice that perl is not itself written in Perl.

The new, native-code compiler for Perl may eventually reduce the
limitations given in the previous statement to some degree, but understand
that Perl remains fundamentally a dynamically typed language, not
a statically typed one.  You certainly won't be chastised if you don't
trust nuclear-plant or brain-surgery monitoring code to it.  And Larry
will sleep easier, too--Wall Street programs not withstanding. :-)

=head2 What's the difference between "perl" and "Perl"?

One bit.  Oh, you weren't talking ASCII? :-) Larry now uses "Perl" to
signify the language proper and "perl" the implementation of it,
i.e. the current interpreter.  Hence Tom's quip that "Nothing but perl
can parse Perl."  You may or may not choose to follow this usage.  For
example, parallelism means "awk and perl" and "Python and Perl" look
OK, while "awk and Perl" and "Python and perl" do not.  But never
write "PERL", because perl isn't really an acronym, apocryphal
folklore and post-facto expansions notwithstanding.

=head2 Is it a Perl program or a Perl script?

Larry doesn't really care.  He says (half in jest) that "a script is
what you give the actors.  A program is what you give the audience."

Originally, a script was a canned sequence of normally interactive
commands--that is, a chat script.  Something like a UUCP or PPP chat
script or an expect script fits the bill nicely, as do configuration
scripts run by a program at its start up, such F<.cshrc> or F<.ircrc>,
for example.  Chat scripts were just drivers for existing programs,
not stand-alone programs in their own right.

A computer scientist will correctly explain that all programs are
interpreted and that the only question is at what level.  But if you
ask this question of someone who isn't a computer scientist, they might
tell you that a I<program> has been compiled to physical machine code
once and can then be run multiple times, whereas a I<script> must be
translated by a program each time it's used.

Perl programs are (usually) neither strictly compiled nor strictly
interpreted.  They can be compiled to a byte-code form (something of a
Perl virtual machine) or to completely different languages, like C or
assembly language.  You can't tell just by looking at it whether the
source is destined for a pure interpreter, a parse-tree interpreter,
a byte-code interpreter, or a native-code compiler, so it's hard to give
a definitive answer here.

Now that "script" and "scripting" are terms that have been seized by
unscrupulous or unknowing marketeers for their own nefarious purposes,
they have begun to take on strange and often pejorative meanings,
like "non serious" or "not real programming".  Consequently, some Perl
programmers prefer to avoid them altogether.

=head2 What is a JAPH?

These are the "just another perl hacker" signatures that some people
sign their postings with.  Randal Schwartz made these famous.  About
100 of the earlier ones are available from
http://www.perl.com/CPAN/misc/japh .

=head2 Where can I get a list of Larry Wall witticisms?

Over a hundred quips by Larry, from postings of his or source code,
can be found at http://www.perl.com/CPAN/misc/lwall-quotes.txt.gz .

Newer examples can be found by perusing Larry's postings:

    http://x1.dejanews.com/dnquery.xp?QRY=*&DBS=2&ST=PS&defaultOp=AND&LNG=ALL&format=terse&showsort=date&maxhits=100&subjects=&groups=&authors=larry@*wall.org&fromdate=&todate=

=head2 How can I convince my sysadmin/supervisor/employees to use version 5/5.005/Perl instead of some other language?

If your manager or employees are wary of unsupported software, or
software which doesn't officially ship with your operating system, you
might try to appeal to their self-interest.  If programmers can be
more productive using and utilizing Perl constructs, functionality,
simplicity, and power, then the typical manager/supervisor/employee
may be persuaded.  Regarding using Perl in general, it's also
sometimes helpful to point out that delivery times may be reduced
using Perl compared to other languages.

If you have a project which has a bottleneck, especially in terms of
translation or testing, Perl almost certainly will provide a viable,
quick solution.  In conjunction with any persuasion effort, you
should not fail to point out that Perl is used, quite extensively, and
with extremely reliable and valuable results, at many large computer
software and hardware companies throughout the world.  In fact,
many Unix vendors now ship Perl by default.  Support is usually
just a news-posting away, if you can't find the answer in the
I<comprehensive> documentation, including this FAQ.

See http://www.perl.org/advocacy/ for more information.

If you face reluctance to upgrading from an older version of perl,
then point out that version 4 is utterly unmaintained and unsupported
by the Perl Development Team.  Another big sell for Perl5 is the large
number of modules and extensions which greatly reduce development time
for any given task.  Also mention that the difference between version
4 and version 5 of Perl is like the difference between awk and C++.
(Well, OK, maybe it's not quite that distinct, but you get the idea.)
If you want support and a reasonable guarantee that what you're
developing will continue to work in the future, then you have to run
the supported version.  As of April 2001 that probably means
running either of the releases 5.6.1 (released in April 2001) or
5.005_03 (released in March 1999), although 5.004_05 isn't that bad
if you B<absolutely> need such an old version (released in April 1999)
for stability reasons.  Anything older than 5.004_05 shouldn't be used.

Of particular note is the massive bug hunt for buffer overflow
problems that went into the 5.004 release.  All releases prior to
that, including perl4, are considered insecure and should be upgraded
as soon as possible.

In August 2000 in all Linux distributions a new security problem was
found in the optional 'suidperl' (not built or installed by default)
in all the Perl branches 5.6, 5.005, and 5.004, see
http://www.cpan.org/src/5.0/sperl-2000-08-05/

=head1 AUTHOR AND COPYRIGHT

Copyright (c) 1997, 1998, 1999, 2000, 2001 Tom Christiansen and Nathan
Torkington.  All rights reserved.

When included as an integrated part of the Standard Distribution
of Perl or of its documentation (printed or otherwise), this works is
covered under Perl's Artistic Licence.  For separate distributions of
all or part of this FAQ outside of that, see L<perlfaq>.

Irrespective of its distribution, all code examples here are in the public
domain.  You are permitted and encouraged to use this code and any
derivatives thereof in your own programs for fun or for profit as you
see fit.  A simple comment in the code giving credit to the FAQ would
be courteous but is not required.