Bash

Bash (Bourne Again Shell) is a shell and scripting language. It is the program that actually interprets and runs the commands you type in the CLI. When you type ls, cd, git push, or npm install, bash is what processes those commands.

Bash is the default shell on most Linux systems and was the macOS default until 2019 (now zsh, which is nearly identical). Beyond single commands, bash lets you write scripts: sequences of commands saved in a file that run together.

Why AI agents use it. Bash is the execution primitive. When an AI agent needs to do something on your system, from running tests to deploying code, it does it through bash commands. Claude Code’s Bash tool, Codex’s sandboxed execution, every agent runtime’s ability to take action on your machine runs through a shell. Bash is how agents go from reasoning to doing.

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