Editing Exit status (section)

===POSIX===
In [[Unix]] and other [[POSIX|POSIX-compatible systems]], the parent process can retrieve the exit status of a child process using the <code>[[Wait (system call)|wait()]]</code> family of system calls defined in [[wait.h]].<ref name="BD_syswait"/>  Of these, the <code>waitid()</code><ref name="SH_waitid"/> call retrieves the full exit status, but the older <code>wait()</code> and <code>waitpid()</code><ref name="SH_wait"/> calls retrieve only the least significant 8 bits of the exit status.

The <code>wait()</code> and <code>waitpid()</code> interfaces set a ''status'' value of type <code>int</code> packed as a [[bitfield]] with various types of child termination information.  If the child terminated by exiting (as determined by the <code>WIFEXITED()</code> macro; the usual alternative being that it died from an uncaught [[signal (computing)|signal]]), [[Single UNIX Specification|SUS]] specifies that the low-order 8 bits of the exit status can be retrieved from the status value using the <code>WEXITSTATUS()</code> macro.

In the <code>waitid()</code> system call (added with SUSv1), the child exit status and other information are no longer in a bitfield but in the structure of type <code>siginfo_t</code>.<ref name="OpenGroup"/>

POSIX-compatible systems typically use a convention of zero for success and nonzero for error.<ref name="ExitStatus"/>  Some conventions have developed as to the relative meanings of various error codes; for example GNU recommend that codes with the high bit set be reserved for serious errors.<ref name="glibc"/>

BSD-derived OS's have defined an extensive set of preferred interpretations: Meanings for 15 status codes 64 through 78 are defined in [[sysexits.h]].<ref name="FreeBSD"/> These historically derive from [[sendmail]] and other [[message transfer agent]]s, but they have since found use in many other programs.<ref name="sysexits"/>  It has been deprecated and its use	is discouraged.<ref name="FreeBSD"/>

The Advanced Bash-Scripting Guide has some information on the meaning of non-0 exit status codes.<ref name="SpecialMeanings"/>