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

I find things like this are most simply done using the @- and @+ built-in arrays in conjunction with substr as an lvalue

$-[1] contains the offset within the string where the first capture began, while $+[1] contains the offset where it ended. Hence $+[1]-$-[1] is the length of the captured section

This program finds all occurrences of /START(.+?)END/ and edits the captured section -- the region between START and END -- by applying a regex substitution to that substring

You may need to chnage this slightly depending on the real-world data that you're working with

use strict;
use warnings 'all';
use feature 'say';

my $str = 'xx START xx bingo xx bingo xx END xx bingo xx START xx bingo xx END bingo';
my ($start, $end, $pattern, $replacement) = qw/ START END bingo okyes /;

while ( $str =~ /\b$start\b(.+?)\b$end\b/gs ) {
     substr($str, $-[1], $+[1]-$-[1]) =~ s/$pattern/$replacement/g;
}

say $str;

output

xx START xx okyes xx okyes xx END xx bingo xx START xx okyes xx END bingo