env

The version of env bundled in GNU coreutils was written by Richard Mlynarik, David MacKenzie, and Assaf Gordon.[1] It first appeared in 4.4BSD, and is a part of POSIX.1 (with the -i option only).[2]

GNU's env has been extended to handle signals and the current directory.[1] FreeBSD's env supports a custom search path. Extensions found in both versions include -u, for unsetting variables, and -S, for splitting arguments (mainly in shebang).[2]

To print out a list of all environment variables, simply run env without any arguments:

env

To clear the environment (creating a new environment without any existing environment variables) for a new shell:

env -i /bin/sh

To launch the X application xcalc and have it appear on a different display:

env DISPLAY=foo.bar:1.0 xcalc

Note that this use of env is often unnecessary since most shells support setting environment variables in front of a command:

DISPLAY=foo.bar:1.0 xcalc

env may also be used in the hashbang line of a script to allow the interpreter to be looked up via the PATH. For example, here is the code of a very simple Python script:

#!/usr/bin/env python3
print("Hello, World!")

In this example, /usr/bin/env is the full path of the env command. The environment is not altered.

Note that it is possible to specify the interpreter without using env, by giving the full path of the python interpreter. A problem with that approach is that on different computer systems, the exact path may be different. By instead using env as in the example, the interpreter is searched for and located at the time the script is run (more precisely, env does a system call to execvp, which does the job of locating the interpreter and launching it). This makes the script more portable, but also increases the risk that the wrong interpreter is selected because it searches for a match in every directory on the executable search path. It also suffers from the same problem in that the path to the env binary may also be different on a per-machine basis.

• set

The Wikibook Guide to Unix has a page on the topic of: Commands

• env: set the environment for command invocation – Commands & Utilities Reference, The Single UNIX Specification, Issue 7 from The Open Group
• env(1) – Inferno General commands Manual
• env—manual page from GNU coreutils.
• env(1): run a program in a modified environment – OpenBSD General Commands Manual
• env(1): set and print environment – NetBSD General Commands Manual