in reply to searching data lines between keywords

Look into the "scalar-context version" of the .. operator in perlop. E.g. 

while ( <> ) {
  if ( my $c = /^(mykeyword1|mykeyword2)$/../^\Q***END***\E$/ ) {
    next if $c == 1 || $c =~ /E/;
    print;
  }
}

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Update: Simplified second regexp slightly.

the lowliest monk

In Section Seekers of Perl Wisdom