wait    Behaves like wait(2) on your system: it waits for a child
            process to terminate and returns the pid of the deceased
            process, or -1 if there are no child processes. The status is
            returned in $? and "${^CHILD_ERROR_NATIVE}". Note that a return
            value of -1 could mean that child processes are being
            automatically reaped, as described in perlipc.

            If you use "wait" in your handler for $SIG{CHLD}, it may
            accidentally wait for the child created by qx() or system(). See
            perlipc for details.

            Portability issues: "wait" in perlport.