Returns the exit status of the child process that open-pipe created.
The function pipe-exit-status returns the exit status of the child process that open-pipe created.
stream must be a pipe stream object which was returned by a call to open-pipe with save-exit-status non-nil.
If wait is t then pipe-exit-status waits until the child process dies. If wait is nil then pipe-exit-status does not wait, and if the child process is still running it returns nil. The default value of wait is t.
On Microsoft Windows, if close was called on the stream before the child process died, then pipe-exit-status returns exit-status :closed. On Unix-like systems it works after close but for compatibility it should be called only before calling close. If you need to send an end-of-file to the child process but also want to read the exit status, use pipe-close-connection before calling pipe-exit-status, and call close afterwards.
If exit-status is not nil or :closed, it is an integer which is the exit status of the child process. See Interpreting the exit status for the interpretation of the exit status and the signal number.
LispWorks User Guide and Reference Manual - 20 Sep 2017