env

For other uses, see Env (disambiguation).

env is a shell command for Unix and Unix-like operating systems. It is used to either print a list of environment variables or run another utility in an altered environment without having to modify the currently existing environment. Using env, variables may be added or removed, and existing variables may be changed by assigning new values to them.

In practice, env has another common use. It is often used by shell scripts to launch the correct interpreter. In this usage, the environment is typically not changed.

Examples

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 python2
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. 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.

External links

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

Unix command-line interface programs and shell builtins

File system	cat chmod chown chgrp cksum cmp cp dd du df file fsck fuser ln ls mkdir mount mv pax pwd rm rmdir size split tee touch type umask

Processes	at bg chroot cron fg kill killall nice pgrep pkill ps pstree time top

User environment	clear env exit finger history id logname mesg passwd su sudo uptime talk tput uname w wall who whoami write

Text processing	awk banner basename comm csplit cut diff dirname ed ex fmt fold head iconv join less more nl paste printf sed sort spell strings tail tr uniq vi wc xargs yes

Shell builtins	alias cd echo test unset wait

Networking	dig host ifconfig inetd netcat netstat nslookup ping rdate rlogin route ssh traceroute

Searching	find grep locate whatis whereis

Documentation	apropos help man

Miscellaneous	bc dc cal expr lp od sleep true and false

List of Unix utilities

This article is issued from Wikipedia - version of the Wednesday, September 02, 2015. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.

env

Examples

See also

External links