You use $_[2] in parse_rvalue in the last elsif. However, you only ever pass it two arguments, so $_[2] will never have anything in it.

The argument list for parse_rvalue is the same as that for parse_command since you call it as &parse_command. In the last line of the sample script, you only pass two arguments to parse_command, so that's all that will show up in parse_rvalue.

How you fix that depends on what everything is supposed to be doing. :)