Well, you question as written makes very little sense, but I'm wondering if you want something like this:

open FILE, 'myfile.txt' or die "Urgh: $!\n";

while (<FILE>) {
  if (/START TEXT/ .. /END TEXT/) {
    # Do something with the text in $_
    # This will be one line from the file
    # after the line containing 'START TEXT'
    # but before the line containing 'END TEXT'
  }
}
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<http://www.dave.org.uk>

"Perl makes the fun jobs fun
and the boring jobs bearable" - me