sub Replace {
    my( $in, $bak ) = @_;
    
    path( $in )-> copy( $bak ); #rename $in to $bak
    
    my $infh  = path( $bak )->openr_raw;
    my $outfh = path( $in )->openrw_raw;
    
    while( <$infh> ) {
        s{&}{&amp;}g; ## will match more than what you want fix it
        s{&amp;amp;}{&amp;}g;
        s{\s>\s}{&gt;}g;
        s{\s<\s}{&lt;}g;
        print $outfh $_;
    }
  
    close $infh;
    close $outfh;
}