The approach of factoring regex sub-expressions can also be helpful.  $RE{num}{real} is from Regexp::Common. The  $title regex won't properly match something like  '/foo/bar/test.c' so this regex (and the others) may need to be refined; this is easier to do if regexes have been factored into individual components. 

c:\@Work\Perl\monks>perl -wMstrict -le
"use Regexp::Common;
 ;;
 my @lines = (
   'test1.cpp     0.00% of 21     0.00% of 16',
   'test2.c     None   16.53% of 484',
   'test3.h         0.00% of 138    None',
   '/x/y/foo.c      0.00% of 1    None',
   );
 ;;
 my $title   = qr{ \w+ (?: [.] \w+)* }xms;
 my $percent = qr{ $RE{num}{real} % \s+ of \s+ \d+ }xms;
 my $none    = qr{ None }xms;
 ;;
 for my $line (@lines) {
   print qq{line '$line'};
   die qq{bad line: '$line'} unless
     my ($t, $p1, $p2) = $line =~ m{
       \A ($title) \s+ ($percent | $none) \s+ ($percent | $none) \s* \
+z
       }xms;
   print qq{  title: '$t'  pcent1: '$p1'  pcent2: '$p2'};
   }
"
line 'test1.cpp     0.00% of 21     0.00% of 16'
  title: 'test1.cpp'  pcent1: '0.00% of 21'  pcent2: '0.00% of 16'
line 'test2.c     None   16.53% of 484'
  title: 'test2.c'  pcent1: 'None'  pcent2: '16.53% of 484'
line 'test3.h         0.00% of 138    None'
  title: 'test3.h'  pcent1: '0.00% of 138'  pcent2: 'None'
line '/x/y/foo.c      0.00% of 1    None'
bad line: '/x/y/foo.c      0.00% of 1    None' at -e line 1.

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Update: Changed code example to better demonstrate error handling.

In reply to Re: how to extract string by possible groupings? by AnomalousMonk
in thread how to extract string by possible groupings? by adrive

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