# The AI-written shell script that ran from the wrong folder and exited 0: `set -euo pipefail`, and where it still won't save you

> Source: <https://dev.to/penloom_studio_829b7817d3/the-ai-written-shell-script-that-ran-from-the-wrong-folder-and-exited-0-set-euo-pipefail-and-349>
> Published: 2026-10-22 15:38:24+00:00

**Result first:** a four-line script whose `cd` failed (because `BUILD_DIR` was unset) kept going. It printed the wrong working directory, ran its "deploy" line, and **exited 0.** Adding one line, `set -euo pipefail`, made it stop on the first error with exit code 1: `BUILD_DIR: unbound variable`.

``` bash
#!/usr/bin/env bash
set -euo pipefail
cd "$BUILD_DIR/out"
```

**What each flag does (bash's own `help set`):**

`-e`: "Exit immediately if a command exits with a non-zero status."`-u`: "Treat unset variables as an error when substituting."`-o pipefail`: "the return value of a pipeline is the status of the last command to exit with a non-zero status, or zero if no command exited with a non-zero status." Without it, `false | true` counts as success.
**Where `-e` still won't save you (GNU Bash manual):** the shell does not exit when the failing command is part of the test in an `if`, inside a `while`/` until` condition, any command in a `&&` or `||` list except the final one, or a command inverted with `!`. The demo shows `if false; then …; fi` carrying on under `set -e`. Don't treat strict mode as a substitute for checking the commands that matter.

**For AI-assisted scripting:** ask your agent to start every bash script with `set -euo pipefail`, and to quote variables. Then read any `cd`, `rm` or deploy line yourself before running it.

**Do this now:** run `head -3` on your repo's `.sh` files and add strict mode to any that lack it. Then test each one, because scripts that relied on ignored errors will now stop.

*From Penloom Studio's free AI lessons: [penloomstudio.com](https://penloomstudio.com/landing-cogloom-motion.html)*