Question

Here is this line in perl:

open my $fh_echo, '-|' or exec "$sshstr \"$str\"";

Basically it exec’s $sshstr and then the output goes into $fh_echo, somehow. I am curious as to the mechanisms that go behind this operation. Can someone explain what the ‘-|’ means?

Also how does this loads the output into $fh_echo? Does it output it little by little or is $fh_echo simply a handle to the output of exec?

Haha I can’t even google this cuz -| don’t show up in the results.

Answer 1

See perlfork. That’s a forking pipe open.

Basically, |- pipes output to a forked child process, and -| reads (within the child process) from the parent.

From perldoc -f open:

If you open a pipe on the command ‘-‘, i.e., either ‘|-‘ or ‘-|’ with 2-arguments (or 1-argument) form of open(), then there is an implicit fork done, and the
return value of open is the pid of the child within the parent process, and 0 within the child process.

In your example, you’re opening a pipe to read from a child process, then forking, then in the child, replacing the process with $sshstr.