#!/usr/bin/perl

use strict;

use constant {
    MIF_EXTENSION => "\.mif",
    TXT_EXTENSION => "\.txt"
};

my $s0 = 'abcd.txt';
print "s0 =\t$s0\n";
$s0 =~ s/\.txt/\.mif/;
print "s0 =\t$s0\n";

my $s1 = 'efgh.txt';
print "s1 =\t$s1\n";
$s1 =~ s/TXT_EXTENSION/MIF_EXTENSION/;
print "s1 =\t$s1\n";
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Scalar $s0 is substituted correctly, yet $s1 is not. What is required to get constants within substitutions to behave as desired? I was unsuccessful with specifying \Q...

Thanks.