c:\@Work\Perl\monks>perl -wMstrict -le
"'zot' =~ m{ (zot) }xms;
 ;;
 for my $s (
   'http://172.20.37.115:8080/se/1.0/pro/subs/198968/',
   'http://172.20.37.115.8080/se/1.0/pro/123456',
   ) {
   my ($var) = $s =~ m{ (\d+) \z }xms;
   print '$var is ', defined($var) ? '' : 'UN', 'defined';
   print qq{'$s' -> '$var' (\$1 is '$1')};
   }
"
$var is UNdefined
Use of uninitialized value $var in concatenation (.) or string at -e line 1.
'http://172.20.37.115:8080/se/1.0/pro/subs/198968/' -> '' ($1 is 'zot')
$var is defined
'http://172.20.37.115.8080/se/1.0/pro/123456' -> '123456' ($1 is '123456')