use strict;
use warnings;
use File::Find;

my $bak_ext  = '.bak';
my $root_dir = 'C:/Temp/Chris/';

find(\&fix, $root_dir);

sub fix {
    # if the extension fits...
    return if ! /\.xml?/i;
        
    print "Processing $_\n";
    
    # set up in place edit
    local @ARGV = ($_); # 
    local $^I = $bak_ext;
    
    # Edit the file
    while (<>) {
        # Edit $_ (the current line) as required here
        print; # Write out the new version of the line
    }
}