In the beginning, Perl was a language that Larry Wall wrote to print formatted reports.
Due to the extreme report formatting capabilities of the language, Wall decided to call it
the Practical Extract Report Language. Today, Perl is better known as the
Pathological Eclectic Rubbish Lister.
Perl inherits its eclectic nature from languages such as AWK, SED, sh and C. The
combination of these languages made Perl into its own unique language. You will find that
many of your gripes about languages such as C or C++ have been eliminated in Perl. For
example:
- There is no need to compile your Perl scripts explicitly before running them.
- There are many, many useful built-in functions.
- Integers and Strings are cast internally.
- There are fewer core dumps.
- There are no pointers!
On the other hand, Perl does very little error-checking by default, and hence bugs can
easily cause your program to misbehave without producing any error messages. The next
section tells you how to make the Perl interpreter pay a bit more attention to what your
code is doing, so it will detect many of these mistakes and produce an error message.
You may find Perl to be a different, and possibly more "natural" programming language
than some of the other programming languages that you are familiar with. This is in part
due to being designed by someone familiar with linguistics.
- The syntax of Perl allows you write the same statement in many different ways, just as
in English there are many different ways of constructing a sentence with a given meaning.
This is where the Perl slogan comes from: There's More Than
One Way of Doing It -- TIMTOWDI (pronounced "tim-toady"). This
allows you to write code in a way that is most natural to you, instead of making you
conform strictly to a particular style.
- In a natural language such as English, the meaning of a word is dependent on its
context. For example, the word "fish" can be used as a verb, noun, adjective, or adverb:
"You can fish out a fish from a fishy fish-farm, but you can't fish the farm out of a
fished-out farmer". In a similar way, the meaning that Perl gives to an expression often
depends on the surrounding context. For instance, Perl is not very picky about the
differences between numbers and strings, and will convert one into the other whenever it
is required. That is, 2 + "66" will evaluate to
68, and "xyz" . 2 to
the string "xyz2" (the period is the string
concatenation operator).
Perl can be used for small jobs (scripts), or for much larger applications. For
instance, the original version of WebCT consisted of over 50,000 lines of Perl. But one of
the nicest things about learning Perl and using it to make your life easier is that very
useful programs can be squeezed into a single line. For example,
% perl -i -pe 's@search pattern@replace pattern@g' file
replaces all occurrences of search pattern with
replace pattern in file,
something that is often useful but difficult to do in UNIX without some
scripting knowledge (do not worry about the syntax for now). As another example, just
recently HotWired's Webmonkey
published an entire search engine written in 4 lines of Perl. However, this programming
practice often makes for unreadable "write-only" programs, and we strongly urge you
not to attempt this kind of feat.
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Why is it that Perl is so often associated with a camel? There are numerous
explanations, ranging from Biblical references to a random selection. The camel is a
funny and awkward looking animal at first glance, and not the most attractive animal
in the wild kingdom. But, when you find yourself in the extreme harshness of the
desert, it won't take long for you to appreciate this extremely well adapted and
versatile creature. At times the desert seems a much more tranquil and safe place
than a UNIX environment. Here is a quote playing on the idea of a camel being
designed by a committee:
No committee could ever come up with anything as revolutionary as a camel --
anything as practical and as perfectly designed to perform effectively under such
difficult conditions.
--Laurence J. Peter
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How To Run and Debug a Perl Script
Back to the introduction