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Environment and Shell variables In Linux

We discuss the differences between environment and shell variables in Linux and provide some examples, as well as discuss how to implement them.
© Wellcome Genome Campus Advanced Courses and Scientific Conferences

In computer operating systems, an environment is an area that contains information about the behaviour of programs and applications.

Linux environment variables are used by applications to get information about the environment, and each environment variable is a variable with a name and an associated value.

Every time the environment is configured a new shell session is created, and this can be used as a learning experience to see how changing Linux environment variables can change things like the appearance of the shell, create paths to executable files, keyboard layout settings, and defining the default home directory for example.

Variables have the following format and by convention have upper case names. Though they are case-sensitive, so it is possible to have lower case names. Also, there is no space around the equals = symbol.

KEY=value KEY=”Another value”

If you assign multiple values to a variable then separate them with a colon : character.

KEY=value1:value2

There are two types of variables:

Environment variables are system wide and are inherited by all system processes and shells.

Shell variables only apply internally to the current shell instance.

How do we use Linux commands to list and set environment variables?

This can be achieved by using the following commands.

env – This allows you to run another program in a custom environment without modifying the current one. When used without an argument it will print a list of the current environment variables.

printenv – This prints all the specified environment variables. For example, to display the value of the HOME environment variable type:

printenv HOME

 

This will print out the path of the currently logged in user.

 

/home/manager

 

You can also pass more than one argument to the printenv command, in the form:

 

printenv <argument1><argument 2>

 

Try this example

 

printenv LANG PWD

 

This will produce an output similar to this one.

 

en_GB.UTF-8

 

Running printenv without any arguments will show a list of all the environment variables.

 

printenv

 

This will produce an extensive output similar to the truncated one below.

 

CLUTTER_IM_MODULE=xim
LS_COLORS=rs=0:di=01;34:ln=01;36:mh=00:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or=40;31;01:mi=00:su=37;41:sg=30;43:ca=30;41:tw=30;42:ow=34;42:st=37;44:ex=01;32:*.tar=01;31:*.tgz=01;31:*.arc=01;31:*.arj=01;31:*.taz=01;31:*.lha=01;31:*.lz4=01;31:*.lzh=01;31:*.lzma=01;31:*.tlz=01;31:*.txz=01;31:*.tzo=01;31:*.t7z=01;31:*.zip=01;31:*.z=01;31:*.Z=01;31:*.dz=01;31:*.gz=01;31:*.lrz=01;31:*.lz=01;31:*.lzo=01;31:*.xz=01;31:*.zst=01;31:*.tzst=01;31:*.bz2=01;31:*.bz=01;31:*.tbz=01;31:*.tbz2=01;31:*.tz=01;31:*.deb=01;31:*.rpm=01;31:*.jar=01;31:*.war=01;31:*.ear=01;31:*.sar=01;31:*.rar=01;31:*.alz=01;31:*.ace=01;31:*.zoo=01;31:*.cpio=01;31:*.7z=01;31:*.rz=01;31:*.cab=01;31:*.wim=01;31:*.swm=01;31:*.dwm=01;31:*.esd=01;31:*.jpg=01;35:*.jpeg=01;35:*.mjpg=01;35:*.mjpeg=01;35:*.gif=01;35:*.bmp=01;35:*.pbm=01;35:*.pgm=01;35:*.ppm=01;35:*.tga=01;35:*.xbm=01;35:*.xpm=01;35:*.tif=01;35:*.tiff=01;35:*.png=01;35:*.svg=01;35:*.svgz=01;35:*.mng=01;35:*.pcx=01;35:*.mov=01;35:*.mpg=01;35:*.mpeg=01;35:*.m2v=01;35:*.mkv=01;35:*.webm=01;35:*.ogm=01;35:*.mp4=01;35:*.m4v=01;35:*.mp4v=01;35:*.vob=01;35:*.qt=01;35:*.nuv=01;35:*.wmv=01;35:*.asf=01;35:*.rm=01;35:*.rmvb=01;35:*.flc=01;35:*.avi=01;35:*.fli=01;35:*.flv=01;35:*.gl=01;35:*.dl=01;35:*.xcf=01;35:*.xwd=01;35:*.yuv=01;35:*.cgm=01;35:*.emf=01;35:*.ogv=01;35:*.ogx=01;35:*.aac=00;36:*.au=00;36:*.flac=00;36:*.m4a=00;36:*.mid=00;36:*.midi=00;36:*.mka=00;36:*.mp3=00;36:*.mpc=00;36:*.ogg=00;36:*.ra=00;36:*.wav=00;36:*.oga=00;36:*.opus=00;36:*.spx=00;36:*.xspf=00;36:
LESSCLOSE=/usr/bin/lesspipe %s %s
XDG_MENU_PREFIX=gnome-
LANG=en_GB.UTF-8
DISPLAY=:0
GNOME_SHELL_SESSION_MODE=ubuntu
COLORTERM=truecolor
USERNAME=manager
XDG_VTNR=1
SSH_AUTH_SOCK=/run/user/1000/keyring/ssh
XDG_SESSION_ID=1
USER=manager
DESKTOP_SESSION=ubuntu
QT4_IM_MODULE=xim
TEXTDOMAINDIR=/usr/share/locale/
GNOME_TERMINAL_SCREEN=/org/gnome/Terminal/screen/f05913a2_61f0_4166_8fd7_9a75b1b624d0……..

 

Some of the more common environment variables are highlighted below.

 

 

Command Description
printenv USER Current logged in user
Printenv HOME Home directory of the current user
Printenv EDITOR The default editor
SHELL The path of the current user’s shell
LOGNAME The name of the current user
PATH A list of directories to be searched when executing commands
LANG The current locales settings
TERM The current terminal emulation
MAIL Location of where the user mail is stored

 

set – This sets or unsets shell variables. If used without an argument then it will print a list of all variables, both shell and environment, and shell functions.

 

Type set in a terminal and it will produce a long list of all the variables.

 

BASH=/bin/bash
BASHOPTS=checkwinsize:cmdhist:complete_fullquote:expand_aliases:extglob:extquote:force_fignore:histappend:interactive_comments:progcomp:promptvars:sourcepath
BASH_ALIASES=()
BASH_ARGC=()
BASH_ARGV=()
BASH_CMDS=()
BASH_COMPLETION_VERSINFO=([0]="2" [1]="8")
BASH_LINENO=()
BASH_SOURCE=()
BASH_VERSINFO=([0]="4" [1]="4" [2]="20" [3]="1" [4]="release" [5]="x86_64-pc-linux-gnu")
BASH_VERSION='4.4.20(1)-release'
CLUTTER_IM_MODULE=xim
COLORTERM=truecolor
COLUMNS=80
DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus
DESKTOP_SESSION=ubuntu
DIRSTACK=()
DISPLAY=:0
EUID=1000
GDMSESSION=ubuntu………

 

unset – This deletes shell and environment variables.

 

export – This command sets environment variables.

 

Examples

 

Below are a few examples highlighting the difference between Environment and Shell variables. We’ll first create a Shell variable and then transform it into an Environment variable.

 

Create a new variable called MY_VARIABLE and give a value of Linux_Variable.

 

MY_VARIABLE=’Linux_Variable’

 

Verify the variable exists by typing:

 

echo $MY_VARIABLE

 

This will display:

 

Linux_Variable

 

Use the printenv command to check whether MY_VARIABLE is an environment variable or not. If the output is empty then it is not an environment variable.

 

printenv MY_VARIABLE

 

This will display no output.

 

Now we have our Shell variable, we can transform it into an Environment variable by typing:

 

export MY_VARIABLE

 

Check MY_VARIABLE exists by typing

 

printenv MY_VARIABLE

 

This time, the variable will now be displayed as it is an Environment variable:
Linux_Variable

 

Please note that variables created in this manner will only be available in the current session, and will be lost when you log out or open a new shell.

 

In order to make the Environment variables persistent you’ll need to add them to specific Linux files.

 

Edit the following file using the nano editor.

 

nano /etc/environment

 

Add MY_VARIABLE=value to a new line and Save. Define your value accordingly. This could be text or a number for example.

 

Another useful method, if you are using Bash, is to declare your variable in the hidden .bashrc profile file.

 

nano ~/.bashrc

 

Add in a new line to the .bashrc file

 

export MYVARIABLE=” value”

 

Save and update the changes to the .bashrc file by typing

 

source ~/.bashrc
© Wellcome Genome Campus Advanced Courses and Scientific Conferences
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