Perl 101 (part 6) - The Perl Toolbox - Expressing Yourself (
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One of Perl's most
powerful features is the ability to do weird and wonderful things with "regular
expressions". To the uninitiated, regular expressions, or "regex", are patterns
which are built using a set of special characters; these patterns can then be
compared with text in a file, or data entered into a Web form. A pattern match
can trigger some kind of action...or not, as the case may be.
Though
regular expressions can get a little confusing when you're first starting out
with them, a little patience will reap rich rewards, as they can save you a
tremendous amount of work. Our very first example illustrates a simple
pattern-matching operation, and introduces you to Perl's match operator:
#!/usr/bin/perl
# get a line of input
print "Gimme a line!\n";
$line = ;
chomp ($line);
# get a search term
print "Gimme the string to match!\n";
$term = ;
chomp ($term);
# check for match
if ($line =~ /$term/)
{
print "Match found!\n";
}
else
{
print "No match found\n";
}
A quick explanation is in order here. In Perl, the "pattern" is the sequence of
characters to be matched - this pattern is usually enclosed within a pair of
slashes. For example,
/xyz/ represents the pattern "xyz".
The
example above asks for a line of text and a search term - this search pattern is
then used with the match operator =~ to test for a match. The result of the =~
operation is true if the pattern is found in the string, and false if
not.
Here's the output of the example above:
Gimme a line!
I'll be back
Gimme the string to match!
b
Match found!
Perl also has the !~ operator, which does the reverse of the =~ operator - it
returns true if a match is NOT found.
This article copyright Melonfire 2000. All rights
reserved.
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