How to perform search-and-replace within given $start-$end ranges?

Question

Say, a text file have many $start-$end pairs, and within each pair there are some text. I want Perl to find-and-replace all $patterns with the

Answer 1

Split each line on START on END, keep a flag that tells you whether you are inside a range or not.

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

my $inside;
while (<>) {
    my @strings = split /(START|END)/;
    for my $string (@strings) {
        if ('START' eq $string) {
            $inside = 1;

        } elsif ('END' eq $string) {
            undef $inside;

        } elsif ($inside) {
            $string =~ s/bingo/okyes/g;

        }

        print $string;
    }
}

Or a bit shorter using a hash as a switch:

#!/usr/bin/perl
use warnings;
use strict;
use Syntax::Construct qw{ // };

my $inside;
while (<>) {
    my @strings = split /(START|END)/;
    for my $string (@strings) {
        $inside = { START => 1,
                    END   => 0,
                  }->{$string} // $inside;

        $string =~ s/bingo/okyes/g if $inside;
        print $string;
    }
}