Be aware that each element in @lines
will have the trailing newline from the file. You probably want to chomp(@lines);
before you compare it against anything.
In addition, your grep statement is non-sensical. See the documentation for it. If you want to loop through @lines and compare it against $ARGV (why not $zero_arg?), you'll have to either explicitely set up a loop to do it, or modify your grep statement to compare against $_, which will iteratively contain each element in @lines in turn.