Show the environment or run a program in a modified environment.

# To show the environment:
env

# To run a program. Often used in scripts after the shebang (#!) for looking up the path to the program:
env <program>

# To clear the environment and run a program:
env -i <program>

# To remove variable from the environment and run a program:
env -u <variable> <program>

# To set a variable and run a program:
env <variable>=<value> <program>

# To set multiple variables and run a program:
env <variable1>=<value> <variable2>=<value> <variable3>=<value> <program>