Well, the general answer to your question is: regular expresion. Below is an example of your question/answer:

#!/usr/bin/perl -w

use strict;

my @test_strings = ("One flew over the cuckoo's nest", "1 flew over th
+e cuckoo's nest");

foreach my $match_string (@test_strings) {
if ($match_string =~ /\d+/) {
print "My matching string is\: $match_string\n";
 }
}
[download]

If you run this, it will print:

"My matching string is: 1 flew over the cuckoo's nest",

because the regular expression /\d+/ matched the "1" in that string. Notice, that it completely ignored "One flew over the cuckoo's nest", because it did not match our regular expression.
\d means digit character, while "+" means one, or more.

For more on regexen, see this, or this, do a Super Search on regular expressions, or, if on a *nix machine, type perldoc perlre.

HTH,
Steve