The previous replies might be good guesses about the nature of your goal, or about what you're doing wrong, but your main problem is that you haven't told us enough about what you are actually doing (apart from what you are trying to do, which is also a bit vague).

What sort of interactive command are you trying to run? (Hint: if it has anything to do with logging into some remote host, that affects what the solution ought to be.)

Is it your intention that the person running the perl script is supposed to type things (after the perl script starts the "interactive command") and these things are then conveyed to (acted on by) the child command process? If so, what sort of value is the perl script supposed to be adding (that is, why use a perl script at all, rather than just running the "interactive command" directly)? If not, just what are you trying to accomplish?

You might need IPC::Open2 (or Open3), or you might need Expect. When you us only vague information, we can only give you back vague advice.