Understanding the Env Command

The env command in Unix-like operating systems is a powerful utility for managing environment variables. It allows you to view, set, unset, and execute commands within a modified environment. This guide will walk you through its common uses and syntax.

Listing Environment Variables

To display all exported environment variables along with their current values, simply run the env command without any arguments.

env

Setting Environment Variables for a Command

You can set a specific environment variable for the duration of a single command. This is useful for temporarily configuring an application or script without altering your global environment.

env <variable>=<value> <command>

For instance, to set a DEBUG variable to true for a script named my_script.sh:

env DEBUG=true ./my_script.sh

Setting Multiple Environment Variables

The env command also supports setting multiple environment variables simultaneously before executing a command.

env <variable_1>=<value> <variable_2>=<value> <command>

Example:

env API_KEY=abcdef123 USER=admin ./run_app.sh

Unsetting Environment Variables

To execute a command with a specific environment variable removed from its inherited environment, use the -u option.

env -u <variable> <command>

This is helpful when you want to ensure a command does not pick up a particular variable from the parent shell.

Clearing the Environment

The -i option allows you to run a command in an entirely clean environment, meaning it will not inherit any variables from the current shell. This is the most restrictive way to run a command.

env -i <command>

This is often used for testing or ensuring a command runs in a predictable, isolated state.

Further Reading

• env man page
• MDN Web Docs on Dates (for context on time-related variables)