Perl 101 (part 6) - The Perl Toolbox - Aardvark, Anyone? (
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The
example you just saw was pretty cut-and-dried - decide search term, decide
replacement term, shove both into Perl script, bang bang and Bob's your uncle.
But what happens if you need to replace a class of words, rather than a single
word? If, for example, you need to replace not just the letter "a", but words
beginning with one or more "a" and ending with a "k"...like "aardvark", for
example?
The special characters you'll use to modify your pattern are
called "metacharacters", which is another of those words that sounds impressive
but means absolutely nothing useful. We'll explain some of them here, and point
you to a resource for more information a little further down.
Two of the
more useful metacharacters in Perl are the "+" and "*" characters, which match
"one or more" instances and "zero or more" instances of the preceding pattern
respectively.
For example,
/boo+/
would match "book", and "booo" but not "bottle", while
/bo*/
would match all of "bottle", "bog", "book", and "booo". One common use of Perl
pattern-matching is to remove unnecessary blank spaces from a block of text.
This is accomplished using the "\s" metacharacter, which matches whitespace, tab
stops and newline characters. The simple substitution
/\s+/ /
would "substitute zero or more occurrences of whitespace with
nothing"
Perl also has two important "anchor" characters, which allow you
to build patterns which specify which characters come at the beginning or end of
a string. The ^ character is used to match the beginning of a string, while the
$ character is used to match the end. So,
/^h/
would match "hello" and "house", but not "shop"
while
/g$/
would match "dig" and "bog", but not "gold" or "eagle"
And you can even
specify more than one pattern to match with the | operator.
/(the|a)/
would return true if the string contained either "the" or "a".
Obviously,
regular expressions is a topic in itself - if you're interested, we've put
together a well-written, comprehensive guide to the topic at
So What's A $#!%% Regular Expression, Anyway?!
This article
copyright Melonfire 2000. All rights
reserved.
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