open all files grab all lines from file 2 - split each line into 2 strings( $number, $year) concatenate $number.$year into one $searchvalue make hash with keys of $searchvalue and values=1 for each line in file1: split each line into 3 strings( $number2,$year2,$string2 ) concatenate $number2.$year2 into one $searchvalue2 look for that key in the hash if it is there, spit the line