use strict;
use warnings;
use Benchmark qw(cmpthese);

my $fileName = "data1";
my $string = $ARGV[0] || die "\nNo Search String Provided.$!\n\n";
my $stringRegex = qr{$string};
my $headerRegex = qw{^Header};  ## Match Headers
my $greenRegex = qr{(^Header).*)};
my $redRegex = qr{($string)};

cmpthese (1, {
    case1 => sub {&case1},
    case2 => sub {&case2},
    },
);

sub case1 {
    my $matches = `grep -h -F -C50 '$grepString' $fileName`;
    my $match; my $data; my $header;

    for (split /^/, $matches) {  ## More efficient than array? (Scalars use less memory)
        if ($_ =~ $headerRegex) {  ## Match headers
            if ($match) {
                $data =~ s/$greenRegex/\033[1;32m$1\033[m/o;  ## Color headers in GREEN
                $data =~ s/$redRegex/\033[1;31m$1\033[m/go;  ## Color string matches in RED
                $data =~ s/\n\n/\n/go;  ## Remove double blanks lines
                print $data, "\n";
                $match = 0;
            }
            $data = ""; $header = 1;
        }
        if (($header) && (0 > index ($_, $string))) {  ## Match body of section
            $data .= $_;
        } elsif ($header) {  ## Match search string
            $data .= $_;
            $match = 1;
        }
    }
}

sub case2 {
    open(my $fh, '<', "$fileName") or die $!;
    my $match; my $data; my $header;

    while (<$fh>) {
        if ($_ =~ $headerRegex) {
            if ($match) {
                $data =~ s/$greenRegex/\033[1;32m$1\033[m/o;
                $data =~ s/$redRegex/\033[1;31m$1\033[m/go;
                $data =~ s/\n\n/\n/go;
                print $data, "\n";
                $match = 0;
            }
            $data = ""; $header = 1;
        }
        if (($header) && (0 > index ($_, $string))) {
            $data .= $_;
        } elsif ($header) {
            $data .= $_;
            $match = 1;
        }
    }
}

case1 4.79 s/iter
case2 46.6 s/iter