Environment Variables and PATH in Linux

Environment variables are dynamic values used by the shell and programs to configure behavior. They are stored as key-value pairs and affect how processes run.

Common Environment Variables

Viewing Environment Variables

printenv       # List all environment variables
echo $HOME     # Show value of a specific variable
env            # Another way to list current environment

Setting Environment Variables

Temporary (for current session only):

VARIABLE_NAME=value

Example:

MY_VAR=hello
echo $MY_VAR   # Output: hello

Exporting (to make it available to subprocesses):

export VARIABLE_NAME=value

Example:

export MY_NAME="Alice"

Making Variables Permanent

To persist variables across sessions, define them in:

• ~/.bashrc or ~/.bash_profile (for Bash)
• ~/.zshrc (for Zsh)

Example:

export MY_NAME="Alice"

Then reload:

source ~/.bashrc

The PATH Variable

What is PATH?

PATH is an environment variable that tells the shell where to look for executable programs.

echo $PATH

Typical output:

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

Adding a Directory to PATH Temporarily:

export PATH=$PATH:/your/custom/path

Example:

export PATH=$PATH:/opt/myapp/bin

Making PATH Change Permanent:

Add to your shell config file:

echo 'export PATH=$PATH:/opt/myapp/bin' >> ~/.bashrc
source ~/.bashrc

Best Practices

• Use export for variables needed by subprocesses.
• Avoid overwriting PATH entirely; always append or prepend.
• Use lowercase for custom temporary variables to avoid conflicts (e.g., my_var).