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

##</code><code>##

c:\@Work\Perl\monks>perl -wMstrict -le
"my $regex = qr/(2[0-4]|1?[0-9])?[0-9]|25[0-5]/;
  while (<>) {
      chomp;
      if ($_ =~ /^$regex$/) {
          print qq{'$_' matched};
      } else {
          print qq{'$_' did not match};
      }
  }
"
0
'0' matched
1
'1' matched
100
'100' matched
1000
'1000' did not match
25
'25' matched
255
'255' matched
256
'256' did not match
a1
'a1' did not match
1a
'1a' did not match
11
'11' matched
111
'111' matched
222
'222' matched
333
'333' did not match