Taking It for a Spin
That’s a lot of information to digest at one sitting. Let’s put some of this into practice to help you get a better grasp of it. For this test drive, we’ll be using the script shown in Example 7-1.
Example 7-1. A simple script to demonstrate regular expression behavior
#!/usr/bin/perl -w # regex.plx # test regular expression behavior $string = 'Walnuts are very nutritious.'; if ($string =~ /Walnuts/) { print "Match!\n"; } else { print "No match!\n"; }
Running this script should yield the following output:
[jbc@andros regex]$ regex.plx
Match!
This shouldn’t be terribly surprising. We’re looking for
the literal string Walnuts
, which occurs inside
the string, so we have a match.
Let’s try out that fancy word-boundary backslash sequence
\b
. We can do that by modifying the line
containing the regular expression in regex.plx
to
look like this:
if ($string =~ /Wal\bnuts/) {
Now when we run the script we should get the following:
[jbc@andros regex]$ regex.plx
No match!
The \b
makes it so that the expression can no
longer match, since it doesn’t have a word boundary between
Wal
and nuts
.
Now change that \b
to a \B
(which says there isn’t a word boundary at that location):
if ($string =~ /Wal\Bnuts/) {
When we run the script it should give us:
[jbc@andros regex]$ regex.plx
Match!
Notice how the \B
sequence doesn’t actually
take up any space in the match. That is,
/Wal\Bnuts/
can still match the string
Walnuts
, even though it has that
\B
sequence stuck in the middle of it. The ...
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