It sounds to me like you want a program that does the following:

• Read each line of your data file: see perlintro (see "Files and I/O" and "Conditional and looping constructs")
• Split your line into tokens: see split, perlre
• Compare the sixth element to see if it is what you want to use: see perlop
• Emit the output you want using the data you are interested in: see print

If you don't know what the last residue number is, you will also need to check that three more values exist in your file prior to emitting the output. Update: A FIFO (push data on the front end of an array during your reads, shift it off the back end of the array during your print) would be one structure that could fit this function.

A note on perlmonks: you will find that you will often get a better discussion on your problem if you present code that you have tried and are getting stuck on. What you have provided is a work request ("Write my code for me for free"). There are many monks that will contract for work, given agreeable terms, but also monks that respond poorly to this no-effort-shown type of request.

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