Current Perl documentation can be found at

Here is our local, out-dated (pre-5.6) version:

It does, but probably not how you expect it to. On systems that follow the standard fork()/exec() paradigm (such as Unix), it works like this: open() causes a fork(). In the parent, open() returns with the process ID of the child. The child exec()s the command to be piped to/from. The parent can't know whether the exec() was successful or not - all it can return is whether the fork() succeeded or not. To find out if the command succeeded, you have to catch SIGCHLD and wait() to get the exit status. You should also catch SIGPIPE if you're writing to the child -- you may not have found out the exec() failed by the time you write. This is documented in the perlipc manpage.

On systems that follow the spawn() paradigm, open() might do what you expect - unless perl uses a shell to start your command. In this case the fork()/exec() description still applies.