you must use open against a program to read from (pipe sign at the end) open my $cmd,"/path/to/prog|"

If you read carefully the open page you'll find many examples.

Also of interest is this section of perlipc

Then you can read from it as for normal filehandles.

There are many other and refined options like IPC::Open2 and IPC::Open3 but also IPC::Run and Capture::Tiny

L*