Acknowledgement: this comment is here thanks to this post and the resulting thread :)

No need to disable warnings, you don't need chr at all:

#!/usr/bin/perl
use warnings;
use strict;
 
my $str0 = "C:/Build~~/Win/App/Experiments/1_0/";
my $str1 = "${str0}Experiments/Blood Pressure/_pieces";
my $str2 = "${str0}temp/Blood Pressure/_pieces";
 
my $commonLen = 0;
($str0 ^ $str1) =~ /^(\0*)/;
$commonLen = $+[0];
 
my $commonStr = substr $str1, 0, $commonLen, "";
substr $str2, 0, $commonLen, "";
 
print "Common: $commonStr\n";
print "Tail 1: $str1\n";
print "Tail 2: $str2\n";
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