Just wrote up a small pseudocode for a previous post here.
[sourcecode type="php"]open (IF, "infile.txt");
open (OF, "outfile.txt");
while (my $line = <IF>) {
$count++;
if ($count == 10) {
# Modify
print OF "somethingelse\r\n";
} else {
# Don't modify
print OF $line;
}
}
close(OF);
close(IF);[/sourcecode]