my @test = ( 'foo m 1 m 2 m 3 m 4 bar',
             'foo m 2 m 4 m 7 bar',
             'foo m 1 bar',
             'm 2 foo m 1 bar',
             'foo m 1 c 2 bar',
             'foo m 1 bar m 2',
             'foo m 1 m 5 m 7',
           );

for my $str (@test) {
  my (@match) = $str =~ /(?:^foo |(?<!^)\G)m (\d+) (?=(?:m \d+ )*bar)/g;
  local $" = ', ';
  print "'$str' => (@match)\n";
}