#!/usr/bin/perl
use strict;
use warnings;

my $dir     = 'c:\top\dir\file';
my $oldroot = 'c:\top';
my $newroot = 'c:\newtop';

my $newdir = $dir;

print "Oldroot will be used as the pattern; It is '$oldroot'\n";
print "newdir was: '$newdir'\n";
$newdir =~ s/$oldroot/$newroot/
    or warn "Can't find pattern '$oldroot' in dir string '$newdir'";
print "newdir now: '$newdir'\n\n";

my $oldroot_regex = quotemeta $oldroot;
#$oldroot_regex = '^' . $oldroot_regex; # I would do this to be safe.
print "Escaped pattern is '$oldroot_regex'\n";

print "newdir was: '$newdir'\n";
$newdir =~ s/$oldroot_regex/$newroot/
    or warn "Can't find pattern '$oldroot_regex' in dir string '$newdir'";
print "newdir now: '$newdir'\n\n";

##</code><code>##

    Oldroot will be used as the pattern; It is 'c:\top'
    newdir was: 'c:\top\dir\file'
    Can't find pattern 'c:\top' in dir string 'c:\top\dir\file' at pm_790602_03.pl line 13.
    newdir now: 'c:\top\dir\file'

    Escaped pattern is 'c\:\\top'
    newdir was: 'c:\top\dir\file'
    newdir now: 'c:\newtop\dir\file'