How about writing a routine into your myfile.pl to read input.txt into an array, and then feeding the (input) elements as needed/where needed?

But heed Riales: this would be better advice (less of a WAG) were you to post some code showing what's at issue. You'll do better, also, if you tell us something more specific than "doesn't work as expected." That could mean anything from 'no visible response' to 'my computer starts spitting out $20 gold pieces.'