env

env [options] [VAR=value]... [command]

env runs a program in a modified environment. It can display current environment variables, set new ones, unset existing ones, or run commands with a clean environment.The command is useful for setting variables temporarily or debugging environment issues.

-i, --ignore-environment

Start with empty environment

Remove variable from environment

End lines with NUL, not newline

Change directory before running command

Process and split string into arguments (useful in shebang lines)

Print verbose information for each processing step

Shebang lines:

$ #!/usr/bin/env bash
#!/usr/bin/env python3
#!/usr/bin/env node

$ env NODE_ENV=production npm start
env DATABASE_URL=postgres://... rails console

$ env -i PATH="$PATH" command

$ env | grep PATH
env | sort

Variables shown as:

$ NAME=value
PATH=/usr/bin:/bin
HOME=/home/user

env

Runs command with modified environment

Sets variables for current shell and children

$ # env (one command only)
env VAR=value command

# export (persistent)
export VAR=value
command  # VAR is available

Variables set with env don't persist after command exits. Shell built-ins (like `cd`, `alias`) cannot be run via env since it uses `execvp`. When using `-i`, PATH must be explicitly set for commands to be found. Values containing spaces must be quoted. The `-C` and `-S` options are GNU extensions not available on all platforms.

env has been part of Unix since the early days, included in POSIX standards for environment manipulation.

export(1), printenv(1), set(1)