In most cases it works fine...

Further to choroba's post: MARVion: Your regex doesn't really work at all because almost everything in it is optional (i.e., has the  ? quantifier) except the  (\d+) bit at the end, so it is happy to match with and capture the first group of decimal digits in anything. What are you really after here?

>perl -wMstrict -le
"my @in = (
   'TFS100',
   'TFS 100',
   'TFS-CR100',
   'TFS-CR 100',
   'TFS_100',
   'TFS ID 100',
   'TFS CR 100',
   'TFS ID100',
   'TFS-ID 100',
   'TFS ID:100',
   'TFS-ID: 100',
   '- TFS CR634: STRESS: H 17326,21600,',
   'CR0080588',
   'TFS0080588',
   qw(1234  xxx1234  123xxx  xxx123xxx  123xxx456  xxx123xxx456),
   );
 ;;
 for my $s (@in) {
   $s =~ m{
     [Tt]? [Ff]? [Ss]? [-_\s]? [Cc]? [Rr]? [Ii]? [Dd]? :? \s? (\d+)
     }xms;
   print qq{'$1' <- '$s'};
   }
"
'100' <- 'TFS100'
'100' <- 'TFS 100'
'100' <- 'TFS-CR100'
'100' <- 'TFS-CR 100'
'100' <- 'TFS_100'
'100' <- 'TFS ID 100'
'100' <- 'TFS CR 100'
'100' <- 'TFS ID100'
'100' <- 'TFS-ID 100'
'100' <- 'TFS ID:100'
'100' <- 'TFS-ID: 100'
'634' <- '- TFS CR634: STRESS: H 17326,21600,'
'0080588' <- 'CR0080588'
'0080588' <- 'TFS0080588'
'1234' <- '1234'
'1234' <- 'xxx1234'
'123' <- '123xxx'
'123' <- 'xxx123xxx'
'123' <- '123xxx456'
'123' <- 'xxx123xxx456'
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