Supose I want to parse a big log file (~500MB/4mil lines), which one is faster and use less memory: $ ./parser.pl logfile.log or $ grep 'Jun 14 03:' | ./parser.pl Log file is 24 hours and it will be processed every hour. ------ parser.pl: $in_time = 'Jun 14 03:'; while(<>) { if(/^$in_time/ { # do some processing }else { next; } } -- --beast