exit0

exit0, or an exit code of 0, refers to the conventional value returned by a program to indicate successful termination. Exit statuses communicate the outcome of a process to its parent process, the operating system, or a calling script.

In POSIX and most Unix-like environments, the exit status is an 8-bit value; 0 signifies success, while non-zero values indicate errors or abnormal termination. Shells and many programming languages follow this convention. Common non-zero codes include 1 for a general error and 127 for command not found; 126 can indicate a command that cannot be executed. Some systems encode the cause of termination by signal numbers, where 128+n indicates termination due to signal n.

In C and related languages, programs typically return 0 from main, or use the EXIT_SUCCESS macro, to signal success, while EXIT_FAILURE or non-zero values indicate failure. The exact numeric meanings of non-zero codes are not standardized across all programs; they are defined by each program.

Usage and implications: scripts examine a command’s exit status (for example, in Bash, the special variable $? holds the last command’s exit code). Continuous integration and build systems rely on exit codes to determine whether a step succeeded. While 0 is widely interpreted as success, some programs may have nuanced semantics; it remains best practice to return 0 only on successful completion.

See also: exit status, exit code, status code.