@stuff = ('This is Some text.','This is More text.');
$stext = '/some/i';

($null, $text, $mod) = split(/\//, $stext);

if ($mod and $mod !~ /[^ism]/) {  # a little sanity checking on the modifers
  $mod = "(?$mod)";
} else {
  $mod = '';
}

foreach (grep /$mod$text/, @stuff) {
  print $_, "\n";
}