Intro To 'env' Command In Linux

2023-05-19 - By Robert Elder

     I use the 'env' command to show the current environment variables.  When I run the 'env' command without arguments like this:

env

     I'll see a list of environment variables like the ones you see below:

SHELL=/bin/bash
QT_ACCESSIBILITY=1
COLORTERM=truecolor
XDG_CONFIG_DIRS=/etc/xdg/xdg-ubuntu:/etc/xdg
GNOME_SHELL_SESSION_MODE=ubuntu
XMODIFIERS=@im=ibus
DESKTOP_SESSION=ubuntu
GTK_MODULES=gail:atk-bridge
PWD=/home/robert
LOGNAME=robert
XDG_SESSION_DESKTOP=ubuntu
XDG_SESSION_TYPE=x11
XAUTHORITY=/run/user/1000/gdm/Xauthority
WINDOWPATH=2
HOME=/home/robert
USERNAME=robert
LANG=en_US.UTF-8
KICAD_PATH=/usr/share/kicad
XDG_CURRENT_DESKTOP=ubuntu:GNOME
VTE_VERSION=6003
MANAGERPID=2510
LESSCLOSE=/usr/bin/lesspipe %s %s
XDG_SESSION_CLASS=user
TERM=xterm-256color
LESSOPEN=| /usr/bin/lesspipe %s
USER=robert
GNOME_TERMINAL_SERVICE=:1.115
DISPLAY=:0
SHLVL=1
QT_IM_MODULE=ibus
XDG_RUNTIME_DIR=/run/user/1000
JOURNAL_STREAM=8:68632
XDG_DATA_DIRS=/usr/share/ubuntu:/usr/local/share/:/usr/share/:/var/lib/snapd/desktop
PATH=/home/robert/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin
GDMSESSION=ubuntu
DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus
_=/usr/bin/env

     These environment variables have important effects on how certain programs run.

Running Commands With Extra Environment Variables Using 'env'

     You can use the 'env' command to run other commands with overridden environment variables:

env date

Tue 16 May 2023 11:44:56 AM EDT

     When I run the 'date' command by itself like this:

date

Tue 16 May 2023 11:45:05 AM EDT

     it defaults to Eastern Standard Time, however, I can use the 'env' command to invoke the date command with the 'TZ' environment variable set:

env TZ='America/Los_Angeles' date

     to achieve a different result:

Tue 16 May 2023 08:45:20 AM PDT

Using 'env' To Run Commands From A Different Directory

     I can also use the '-C' flag to invoke the command as if it ran in a different working directory.  All of the following commands were run from the same directory:

     Here is the output from the regular 'pwd' command:

pwd

/home/robert/important

     And here is the result when 'pwd' is run through the 'env' command:

env pwd

/home/robert/important

     Running a command as if we were in the '/home' directory:

env -C /home pwd

/home

     Running a command as if we were in the '/run' directory:

env -C /run pwd

/run

Reset All Environment Variables With 'env' Command

     By default, the 'env' command inherits the existing environment variables, so if you set a new environment variable with 'env' any other environment variable that were previously set will still be present:

env FOO=VAR env

SHELL=/bin/bash
QT_ACCESSIBILITY=1
USERNAME=robert
LANG=en_US.UTF-8
... Many Other Environment Variables
FOO=VAR

     You can unset all of these other environment variables with the '-i' flag:

env -i FOO=VAR env

FOO=VAR

     And that's why the 'env' command is my favourite Linux command.