env Command Cheat Sheet

env allows you to run a command in a modified environment. It is typically used to set or unset environment variables temporarily for a single command execution, or to list current variables.

Synopsis

env [OPTION]... [NAME=VALUE]... [COMMAND [ARG]...]

Basic Usage

List All Environment Variables

Running env without arguments prints all exported environment variables.

env

Run Command with Specific Variable

Set VAR to value only for the duration of command.

env EDITOR=nano crontab -e

Modifying the Environment

Set Multiple Variables

env USER=test PATH=/bin:/usr/bin script.sh

Unset a Variable (-u)

Remove a variable from the environment for the command.

env -u EDITOR crontab -e

Clear Entire Environment (-i)

Run with an empty environment. Useful for testing scripts in isolation to ensure they don't rely on user-specific settings.

env -i /bin/bash

Or combining with specific variables:

# Start with empty env, but add PATH and TERM
env -i PATH=/bin:/usr/bin TERM=xterm /bin/bash

The Shebang Usage

env is standard for shebang lines in scripts because absolute paths to interpreters vary (e.g., python might be in /usr/bin or /usr/local/bin).

Python Script

#!/usr/bin/env python3

Node.js Script

#!/usr/bin/env node

Bash Script

#!/usr/bin/env bash

Debugging

Print Specific Variable

Use printenv generally, but env with grep works too.

env | grep PATH

Trace Execution (-v)

Verbose mode prints processing steps (GNU coreutils 8.30+).

env -v ls

Options Cheat Sheet

Advanced: Breaking Arguments in Shebangs (-S)

Standard shebangs only accept one argument. To pass multiple flags (e.g., awk -f), use -S.

#!/usr/bin/env -S awk -f

Comparison: env vs printenv vs export

Practical Examples

Testing Compilation in Clean Environment

Ensure your build doesn't depend on accidental environment variables.

env -i PATH=$PATH make

Changing Directory Before Running (-C)

Similar to (cd /tmp && ls).

env -C /tmp ls

Force English Locale

Run a command with default English output, ignoring user's language settings.

env LC_ALL=C date
# Output: Sat Feb 14 12:00:00 UTC 2026
# Instead of localized format

Exit Status

Notes

• env is external (/usr/bin/env), unlike export which is a shell builtin.
• Altering PATH with env is a common security risk if untrusted directories are added first.