env

Updated

September 4, 2026

Overview

env runs a program in a modified environment, or prints the current environment variables when given no command. It is essential for shebangs (#!/usr/bin/env bash), clearing the environment (-i), and injecting variables for a single command without exporting them permanently in the shell.

Syntax

env [options] [NAME=VALUE]... [command [args...]]
env                       # print environment

Common Options

Option	Description
`-i`, `--ignore-environment`	Start with an empty environment
`-u NAME`, `--unset=NAME`	Remove variable
`-0`, `--null`	NUL-delimit output
`-C dir`, `--chdir=dir`	Change directory before exec (newer coreutils)
`-S string`	Split string on shebang lines (see man)
`-v`	Verbose
`--`	End of options

Examples with Explanations

Print environment

env
env | sort
env | grep -E '^(PATH|HOME|USER)='
printenv PATH               # single var alternative

Run with extra variables

env FOO=bar BAZ=1 ./script.sh
env NODE_ENV=production node app.js

Equivalent to shell FOO=bar ./script.sh for simple cases; env shines with cleared environments and shebangs.

Clear environment

env -i PATH=/usr/bin:/bin HOME="$HOME" bash --noprofile --norc
env -i $(cat allowed.env | xargs) command

Useful for clean builds and debugging “works in my shell” issues.

Unset for one command

env -u http_proxy -u https_proxy curl -I https://example.com

Shebang portability

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

env locates the interpreter via PATH, avoiding hard-coded /usr/bin/python3 when layouts differ. (Security-sensitive contexts may prefer absolute paths.)

Chdir then run (when supported)

env -C /var/www -i PATH=/usr/bin:/bin ./deploy.sh

NUL-safe dump

env -0 | tr '\0' '\n' | sort

Notes / Pitfalls

env -i is easy to over-strip — many programs need PATH, HOME, TERM, LANG.
Shebang line length limits exist; complex env -S usage has edge cases.
Printing env may leak secrets (AWS_*, tokens) — avoid pasting full dumps.
Order of assignment and -u matters; see man page for processing order.
Shell builtins are not found by env — it execs real programs from PATH.

2026-relevant notes

Container entrypoints often use env or exec forms to inject config.
Prefer explicit .env loading tools or systemd Environment= for services.
Security: LD_PRELOAD and similar can be injected via env — hardened systems scrub them for setuid.

Additional Resources

man env