use strict;
use warnings;
use v5.12;

my $string = "abcdefggggggggggg";

my $position = length( $string ) - 1;

my $find = substr $string, $position, 1;

$position-- while substr( $string, $position, 1 ) eq $find;

substr( $string, $position + 3, length( $string ) - ( $position + 3 ), '') if length( $string ) - $position > 3;

say $string;