ExitStatus

ExitStatus is a representation of how a program or child process terminated. It encodes information about the outcome of execution, typically including an exit code that indicates success or failure and, on some systems, additional details such as termination by a signal.

In POSIX and Unix-like systems, the exit status is delivered to the parent process via wait or waitpid. The status value is examined with a set of macros: WIFEXITED indicates normal termination, WEXITSTATUS yields the exit code (usually in the range 0–255), and WIFSIGNALED indicates termination by a signal, with WCOREDUMP signaling a core dump. The low 8 bits generally carry the exit code, while other bits encode the reason for termination. In shells, the exit status of the most recent foreground command is exposed as a special variable (commonly used as $?).

Windows reports exit codes through the GetExitCodeProcess API. An exit code is a 32-bit value; zero typically means success, but specific programs define nonzero codes to indicate particular errors. Because Windows and POSIX conventions are not identical, portable interpretation of exit statuses must be careful.

In programming languages there are language-specific representations. For example, Rust provides a type named ExitStatus in the standard library to represent the exit status of a child process started with std::process. The code method returns an Option<i32> with the exit code when the child exited normally. On Unix, there is an extension trait that exposes additional details, such as the terminating signal and whether a core dump occurred.

Overall, exit status conveys whether a process finished cleanly and, if not, why it did not succeed. Programs that rely on exit codes should handle the variability across platforms by checking for normal exit first and then interpreting the code accordingly.