#!perl -l
use strict;
use warnings;

my $orig =        'a.dll';
my $replacement = 'b.dll';

my $str1 = "foo $orig bar";
my $str2 = $str1;

$str1 =~ s/\Q$orig\E/\Q$replacement\E/g;
$str2 =~ s/\Q$orig/$replacement/g;

print $str1;
print $str2;

##</code><code>##

foo b\.dll bar
foo b.dll bar

##</code><code>##

$str1 =~ s/\Q$orig\E.+/\Q$replacement\E/g;