use Tie::File;

sub replace_serialnumbers_in_file($)
{
	my @word = qw( zero one two three four five six seven eight nine );
	my $filename = shift;
	my $serno = join '', map $word[$_], $filename =~ /(\d)/; # assuming no other digits in the filename
	tie my @lines, 'Tie::File', $filename or die;
	s/\\zerozerozero/\\$serno/g for @lines;
}