Understanding Path, Shell, and Enviroment Variables in MacOS/Linux

PATH: $PATH in macOS and Linux is like a list of folders your computer looks through to find and run programs or commands.

How It Works:

1. Imagine a Toolbox:

   • The PATH is a list of “toolboxes” (folders) where tools (programs or commands) are kept.
   • When you type a command like python3, the system searches through the folders listed in the PATH to find it.

2. Order Matters:

   • The system looks in the folders in the order they appear in the PATH. The first match it finds is the one it runs.
   • If two versions of python3 are in different folders, the one in the folder listed earlier in the PATH is used.

3. Where Is the PATH?:

   • The PATH is stored in an environment variable called PATH.
   • To see it, type:

     echo $PATH
     

   • Example output:

     /usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin
     

4. Colon as a Separator:

   • Each folder in the PATH is separated by a :.

Why the PATH Matters:

If a program isn’t in a folder listed in the PATH, you’ll get an error like:

command not found

How to Add to the PATH:

If you install a new program and want your system to find it, you add its folder to the PATH.

1. Open your shell configuration file (like ~/.zshrc or ~/.bashrc):

   nano ~/.zshrc
   

2. Add a line to include the folder:

   export PATH="/new/folder:$PATH"
   

   This puts /new/folder at the start of the PATH.

3. Save and reload:

   source ~/.zshrc
   

Now, your computer knows to look in /new/folder first for commands.

Shell: To find out which shell you are using, you can run the following command in your terminal:

echo $SHELL

Output Example:

• /bin/zsh: You’re using Zsh (Z Shell).
• /bin/bash: You’re using Bash.
• /bin/fish: You’re using Fish.
• /bin/sh: You’re using Sh.

To Check the Default Shell:

If you want to know your default shell (the one that starts when you open a new terminal), run:

echo $0

This will also indicate the shell running in the current session.

How to Change the Default Shell:

If you want to switch to a different shell (like Zsh or Bash):

1. List available shells:

   cat /etc/shells
   

   Example output:

   /bin/bash
   /bin/zsh
   /usr/local/bin/fish
   

2. Change your shell (e.g., to Zsh):

   chsh -s /bin/zsh
   

3. Restart your terminal to use the new default shell.

Env: To view environment variables on macOS or Linux, you can use the following commands in your terminal:

1. Show All Environment Variables

To display all currently set environment variables:

printenv

or

env

Both commands output a list of environment variables and their values.

Example output:

PATH=/usr/local/bin:/usr/bin:/bin
HOME=/Users/yourusername
SHELL=/bin/zsh

2. Check a Specific Environment Variable

If you want to see the value of a specific variable, use echo:

echo $VARIABLE_NAME

For example:

echo $PATH

This displays the directories listed in your PATH.

4. Temporarily Set an Environment Variable

To set an environment variable for the current session only:

export MY_VAR="value"
echo $MY_VAR

5. Persist Environment Variables

To make a variable permanent, add it to your shell configuration file (~/.zshrc, ~/.bashrc, etc.):

export MY_VAR="value"

Save the file and reload it:

source ~/.zshrc

6. **Temporarily Adjust Path **

export PATH="/temporary/directory:$PATH"

This will add the temporary directory path to the begining of the $PATH list. This will only be present for the zshell session

• Linux
• Macos