in reply to
Reading files n lines a time
Depending on the way your files-which-need-to-be-read-four-lines-at-a-time (henceforward, "fwn") are formatted/organized and the consistency thereof, you might consider setting your $/ record separator...
for ex, if data looks like:
then setting local $/="\n\n" will tell Perl that you want to read a paragraph from the fwn, where paragraph is defined as something ending in two consecutive newlines. Better yet, the special case, $/="" defines para somewhat more broadly and may be suitable to deal with your data.
You'll find many examples here, if you merely SuperSearch for $/