#!/usr/bin/perl
use Test2::V0;
#FROM DATABASE TEXT
my $line = "Her house is on 34th Mt. Whitney St. near St. Mt. Helens St.";
#FROM INCOMING FORM INPUTS
my $query = qr'(St\.\s)(Mt\.\s)(?=Helens)';
my $substitution = 'Mount ${1}'; # USER MAY HAVE ENTERED "$1"
#FOR RETURNED HTML HIGHLIGHT OF CHANGES
my $start = '';
my $end = '';
my $replace = $start . $substitution . $end;
# twofold quoting and double eval'ing does the trick:
$line =~ s{$query}{"qq{$replace}"}gee;
is $line, 'Her house is on 34th Mt. Whitney St. near Mount St. Helens St.', 'pattern substitution';
done_testing;