Using seek() is in general not a good idea and particularly not for text input.

That is a byte oriented thing and not a character oriented thing.
There are many complications that can arise between bytes and characters.
The translations between "\n" or "\r" or "\r\n" in different O/S'es are well known, but "messy".

open(FILE, "<", "textfile.txt") or die "Cannot open textfile: $!";

while (<FILE>)
{
  print;  #just to get started...
  # something..
}

# using a seek() is almost never "right".
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Show some example input and what you want to do.