On Fri, Sep 9, 2011 at 10:38 PM, Cyril J. <cyril.varghese.jose / gmail.com> wrote: > What is the most efficient way of reading two large files at the same > time without using too much memory? Also, I need to compare strings in > the header lines throughout one file with the other file to weed out > what is different. Just don't know how to start reading the files at the > same time. Any ideas on how to go about starting this? I was thinking a > while loop but wasn't really sure on how to implement it. Small example > would help. Thanks in advance. What exactly are "header lines" in your case? Without knowing the format and your parsing / processing requirements it's difficult to come up with suggestions. The most generic is File.open f1 do |io1| File.open f2 do |io2| # now what? end end Kind regards robert -- remember.guy do |as, often| as.you_can - without end http://blog.rubybestpractices.com/