$CHILD_ERROR
    $?      The status returned by the last pipe close, backtick (``)
            command, successful call to "wait()" or "waitpid()", or from the
            "system()" operator. This is just the 16-bit status word
            returned by the traditional Unix "wait()" system call (or else
            is made up to look like it). Thus, the exit value of the
            subprocess is really ("$? >> 8"), and "$? & 127" gives which
            signal, if any, the process died from, and "$? & 128" reports
            whether there was a core dump.