a) '($str1, $str2) = split/:/ if /:/',
   b) 'if (/:/) {$str1 = $`; $str2 = $\'}',
   c) 'if (/:/) {$str1 = substr($_,0, $-[0]); $str2 = substr($_,$+[0])}'
   d) '($str1,$str2) = m/(\d*):(\d*)/ if /:/'
   e) Too close to call.