Bash vs other shells

Your login shell might be zsh on macOS or fish on a personal machine, but Bash remains the lingua franca for portable scripts and CI images.

Common shells

• sh — POSIX subset; maximum portability for minimal scripts
• bash — extensions: arrays, [[ ]], process substitution
• zsh — macOS default login shell; strong completion and globbing
• fish — friendly UX; not POSIX—poor fit for generic CI scripts

Check your shell

echo "$SHELL"
ps -p $$ -o comm=

$SHELL is your login shell path. ps shows what is running this session.

When to pick Bash

Use Bash when a script must run on generic Linux CI runners and tutorials assume #!/bin/bash. Use zsh/fish locally if you prefer—keep project scripts on Bash unless the team standardizes otherwise.

Important interview questions and answers

1. Q: Why do CI images default to Bash?
   A: Scripts and docs target Bash; POSIX sh is used when portability beats Bash-only features.
2. Q: Can zsh run Bash scripts?
   A: Often yes for simple scripts, but Bash-only syntax breaks—test in Bash explicitly.

Self-check

1. What does the shebang line tell the kernel?
2. Why might a macOS user still learn Bash if zsh is the login shell?

Tip: Write portable project scripts for bash unless your team standardizes on POSIX sh only.