use warnings;
use strict;

while (<DATA>)
  {
  my ($part1, $part2, $part3, $part4) = $_ =~
    /"some text (?:\((.*?)\) )?more text (.*?) and dst text (.*?) -flag (.*?)"/;

  $part1 ||= '';
  print "1: $part1\n2: $part2\n3: $part3\n4: $part4\n";
  }
  
__DATA__
"some text (6\'s and 7\'s) more text fred and dst text joe -flag /tmp/filename"
"some text more text fred and dst text joe -flag /tmp/filename"

##</code><code>##

1: 6\'s and 7\'s
2: fred
3: joe
4: /tmp/filename
1: 
2: fred
3: joe
4: /tmp/filename