#!/usr/bin/env perl
use strict;
use warnings;
use diagnostics;

my @blocklines;
my $inblock = 0;

open(my $IFH, '<', 'blockextract.txt') or die($!);
while((my $line = <$IFH>)) {
    chomp $line;

    if($line =~ /parameters\ after\ change/) {
        # Start of a block we want to read
        $inblock = 1;
        next;
    }

    # Skip handling line unless we are in a block
    next unless($inblock);

    if($line =~ /NRG\ location/) {
        # Block ends here
        # Do whatever you want to do to the block lines
        # stored in @blocklines.
        # I'm just dumping them to STDOUT
        print "*** START ***\n";
        print join("\n", @blocklines), "\n";
        print "*** END ***\n\n";

        # Clean up block
        @blocklines = ();
        $inblock = 0;
        next;
    }

    # just some line within the interesting block
    # remember it for later in @blocklines
    push @blocklines, $line;
    next;
}

close $IFH;

exit(0);