Exit codes and command chaining — &&, ||, and ; explained

When any command finishes, it sets an exit code — a number from 0 to 255 that the shell can check. 0 means success. Anything else means some kind of failure, with the specific non-zero value sometimes indicating which kind (though that convention varies by program). You can see the exit code of the last command with a special shell variable:

This is why mkdir new-folder && cd new-folder is a genuinely safer habit than running the two as separate commands: if mkdir fails (the folder already exists, or you lack permission), cd never runs, instead of silently cd-ing into whatever directory you happened to already be in and continuing as if nothing went wrong.

A shell script can set its own exit code with exit N, which matters because other tools (CI pipelines, cron, other scripts calling yours) rely on it to know whether your script actually succeeded:

A script that always exits 0 regardless of what actually happened — even after printing an error — will report "success" to anything checking its exit code, silently hiding a real failure from whatever's relying on that signal.

Command chaining with && is one of the most common patterns in real scripts and CI pipelines specifically because it enforces "don't proceed past a failure" without extra if statements — and a CI pipeline stage that shows green despite an underlying command failing is almost always traceable back to a script somewhere not propagating its real exit code correctly.