env

run programs with modified environment variables

TLDR

Show all environment variables

$ env

Run command with environment

$ env VAR=value [command]

Clear environment

$ env -i [command]

Unset variable

$ env -u [VAR] [command]

SYNOPSIS

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.

PARAMETERS

-i, --ignore-environment

Start with empty environment

-u var, --unset=var

Remove variable from environment

-0, --null

End lines with NUL, not newline

-C dir, --chdir=dir

Change directory before running command

-S string

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

-v, --verbose

Print verbose information for each processing step

WORKFLOW

$ # Display all environment variables
env

# Set variable for one command
env DEBUG=1 ./program

# Multiple variables
env VAR1=value1 VAR2=value2 command

# Clear environment
env -i command

# Clean environment with specific variables
env -i PATH=/usr/bin HOME=/home/user command

# Unset variable
env -u DISPLAY command

# Change directory first
env -C /tmp ls

# In shebang for portability
#!/usr/bin/env python3

COMMON USES

Shebang lines:

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

Temporary variables:

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

Clean environment:

$ env -i PATH="$PATH" command

Debugging:

$ env | grep PATH
env | sort

VARIABLE FORMAT

Variables shown as:

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

COMPARISON WITH EXPORT

env

Runs command with modified environment

export

Sets variables for current shell and children

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

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

INSTALL

sudo apt install coreutils

sudo dnf install coreutils

sudo pacman -S coreutils

sudo apk add coreutils-env

sudo zypper install coreutils

brew install coreutils

nix profile install nixpkgs#coreutils

CAVEATS

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.

HISTORY

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

env