Bash script: how do I make it fail safely instead of continuing after errors?

Question

My deploy script continued after `npm run build` failed and deployed a broken version. How do I make bash scripts stop on errors?

Accepted Answer

Start every script with **strict mode**:

```bash
#!/usr/bin/env bash
set -Eeuo pipefail
```

- `-e`: exit as soon as any command fails.
- `-u`: error on undefined variables. Catches typos like `rm -rf "$BUILD_DIR/"` when `BUILD_DIR` is empty!
- `-o pipefail`: a pipeline fails if *any* command in it fails, not just the last one.
- `-E`: `ERR` traps also fire inside functions.

Add a trap to report where it failed:
```bash
trap 'echo "❌ Failed at line $LINENO: $BASH_COMMAND" >&2' ERR
```

Other good habits:
- **Quote variables**: `"$file"`, not `$file`.
- Run **ShellCheck** on your scripts. It catches most bash pitfalls.
- When a script grows past ~100 lines or needs real error handling, consider Python or a Makefile or task runner instead.

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