c:\@Work\Perl\monks>perl -wMstrict -le
"my $regex = '(2[0-4]|1?[0-9])?[0-9]|25[0-5]';
while (<>) {
    chomp;
    if ($_ =~ /^$regex$/) {
        print qq{'$_' matched};
    } else {
        print qq{'$_' did not match};
    }
}
100
'100' matched
z100
'z100' did not match
z255
'z255' matched
z250
'z250' matched
100z
'100z' matched
99
'99' matched
9999999
'9999999' matched
99Yikes!99
'99Yikes!99' matched
1
'1' matched
11
'11' matched
111
'111' matched
22
'22' matched
222
'222' matched
33
'33' matched
333
'333' matched