About Bash Profile and Bash.Rc on Mac OS

The macOS Terminal.app uses a series of scripts and configuration files to set up the shell environment before you see the command prompt. Here’s an overview of these files and how they are executed:

1. /etc/profile: This is a system-wide configuration file that is executed for all users when they start a new shell session. It sets up environment variables and configurations that are applicable to all users.

2. /etc/bashrc: This file is also system-wide and is typically sourced (executed) by /etc/profile. It can contain additional configurations and environment variables that apply to all users and all shell sessions.

3. /etc/bashrc_Apple_Terminal: This is a macOS-specific extension of the /etc/bashrc file. It contains configurations that are specifically intended for Terminal.app.

4. ~/.bash_profile: This is a user-specific configuration file that is executed when a user logs in. If this file exists, it takes precedence over other configuration files. Users can use this file to set up their own custom environment variables and configurations.

5. ~/.bash_login: If ~/.bash_profile does not exist, the shell looks for ~/.bash_login and executes it if it’s present. This file is another option for users to customize their shell environment.

6. ~/.profile: If neither ~/.bash_profile nor ~/.bash_login exists, the shell will use ~/.profile for user-specific configurations.

7. ~/.bashrc: Users can optionally choose to source (execute) ~/.bashrc from their ~/.bash_profile. This allows them to keep common configurations in ~/.bashrc and have them applied to both login and non-login shell sessions.

These files and their execution order allow users and system administrators to customize and configure their shell environment to meet their specific needs. It’s important to note that these files are typically written in Bash script, so you can use them to define environment variables, customize the prompt, set aliases, and more to tailor your shell experience on macOS.