What Is an Exit Code? How Commands Report Success

An exit code is a small integer a program returns when it finishes, where 0 means success and any non-zero value means some kind of failure.

When a command finishes, it hands back a number that tells the shell whether it worked. Zero means success; anything else means failure. This single number is what CI uses to decide whether a step passed or failed, which makes exit codes the heartbeat of every pipeline.

What an exit code is

It is the status a process returns on exit, an integer from 0 to 255. The shell stores the most recent exit code in the special variable $?, which you can inspect right after a command runs.

Zero versus non-zero

By convention 0 means the command succeeded. Any non-zero value signals a failure, and different numbers can mean different problems, like a missing file or bad arguments.

Some common codes

0: success.
1: a general, catch-all error.
127: command not found.
130: terminated by Ctrl-C (signal interrupt).

Exit codes and control flow

The shell uses exit codes for logic. cmd && next runs next only if cmd succeeded; cmd || fallback runs fallback only if cmd failed. This is how scripts branch on success.

Exit codes in CI

A CI step passes if its final exit code is 0 and fails otherwise. With set -e, the script aborts on the first non-zero exit, so a failing command immediately fails the job instead of being ignored.

Pass and fail on managed runners

Latchkey runners report a job as failed when a step exits non-zero. Because genuine failures surface as exit codes, transient infrastructure issues can be distinguished and retried while real test or build failures stop the run.

Key takeaways

An exit code is the number a program returns; 0 is success, non-zero is failure.
The shell stores the last exit code in $? and branches on it with && and ||.
CI decides pass or fail from a step's exit code, especially under set -e.