shell-error-handling

Error handling in Bash involves checking exit codes, using set -e to exit on failure, and applying trap commands for cleanup. Standard patterns include validating return values, routing errors to stderr, and executing cleanup routines when scripts exit or encounter failures.

Traps are Bash handlers that execute code when the shell receives signals or exits. Use trap 'cleanup_function' EXIT to run cleanup routines—closing files, removing temporary resources, or logging—automatically when your script terminates, whether normally or due to error.

Defensive shell programming checks prerequisites before execution and validates inputs early. Test for required commands, verify file existence, confirm correct argument counts, and validate data formats. This catches problems immediately and prevents scripts from executing with incomplete or invalid state.

Exit codes signal success or failure to calling processes and enable reliable error detection. Standard conventions—0 for success, non-zero for specific failure types—let scripts chain operations, conditionally branch on results, and communicate failures to automation tools and logs.

Use mktemp to generate unique temporary filenames with restricted permissions, preventing race conditions and unauthorized access. Pair it with trap cleanup to remove temporary resources reliably, even if the script fails or is interrupted.