use strict;
use warnings;

local $/ = 'HEADER(';

while (<DATA>) {
    chomp;

    next unless /(.*\bGENRE_BY\b\(.*\)\s*\))/s;
    print "HEADER($1";
}


__DATA__
HEADER(
   LIBDAT("GTASK")
   VENDOR("DeltaQ")
   Environment("zeronom")
   TASK_VERSION("5.2")
   GENRE_BY("dumpTc")
)

other stuff here

HEADER(
   LIBDAT("GTASK")
   VENDOR("DeltaQ")
   Environment("zeronom")
   TASK_VERSION("5.2.1")
   GENRE_BY("dumpTc")
)