I need to parse a file line by line on given rules. Here is a requirement. file can have multiple lines with different data.. 01200344545143554145556524341232131 1120034454514355414555652434123213101200344545143554145556524341232131 2120034454514 and rules can be like this. if byte[0,1] == "0" then extract this line to /tmp/record0.dat if byte[0,1] == "1" then extract this line to /tmp/record1.dat if byte[0,1] == "2" then extract this line to /tmp/record2.dat I am looking for any language which can do this in a fast manner with a very long file size like 2 GB. Appreciate all the help in advance. Thanks