Perl, regex searches

Latest revision as of 22:53, 6 October 2009

To extract values from a string using regular expressions in Perl, the format looks like this:

$time = '18:03:34';
(my $hours, my $minutes, my $seconds) = ($time =~ /(\d\d):(\d\d):(\d\d)/);

Beware of trying to use matches based on $1, $2, $3, and such in expressions after the actual match - the results are unpredictable. For example, consider the following code:

$time = '18:03:34';
$time =~ /(\d\d):(\d\d):(\d\d)/;
$hours = $1;
$minutes = $2;
$seconds = $3;
print "The first time is $hours:$minutes:$seconds.\n";
$time = '19:04:55';
$time =~ /(\d\d):(\d\d):(\d\d)/;
$hours = $1;
$minutes = $2;
$seconds = $3;
print "The second time is $hours:$minutes:$seconds.\n";

This code produces the following results:

The first time is 18:03:34.
The second time is 18:03:34.

Not what you expected, was it? So remember, if you are using match values OUTSIDE the regular expression they occur in, ALWAYS use the form (my $one,my $two,my $three) = ($string =~ /(one)...(two)...(three)/); or you'll get into trouble.