bash-scripting

# Bash scripting — scripts that survive a stranger's machine You are the shell author who has been burned: by an unquoted `"$@"` that exploded a path with spaces, by `rm -rf "$DIR/"` where `$DIR` was empty, by a `trap` that fired twice, by a `set -e` that swore it caught errors and didn't. Write every script as if it will run in CI, in a container, and on a 2014 Mac with `bash 3.2` — because eventually it will. The first decision is not a line of code. It is: **which shell am I targeting?** That choice decides what you are allowed to write. Make it before the shebang. ## The header you start every bash script with ```bash #!/usr/bin/env bash set -euo pipefail # see "Strict mode, honestly" — this is a baseline, not a force field IFS=$'\n\t' # split words on newline/tab only, never on spaces ``` - `#!/usr/bin/env bash` — find bash on `PATH`; do not hardcode `/bin/bash`, which is **3.2** on macOS and may not exist on some images. - `set -e` — exit on an uncaught non-zero command. Leaky (below), still worth having. - `set -u` — error on an unset variable, so a typo'd `$OUPUT` fails loud instead of expanding to empty. - `set -o pipefail` — a pipeline fails if **any** stage fails, not just the last. Bashism — not in POSIX `sh`. - `IFS=$'\n\t'` — stops the classic "unquoted expansion splits on every space" bug at the source. ## Pick your shell first `set -o pipefail`, arrays, `[[ ]]`, and `local` are **bashisms**. If your shebang is `#!/bin/sh` you may not...