Set variable value linux

Setting environment variables in Linux using Bash

What is the equivalent to the tcsh setenv function in Bash? Is there a direct analog? The environment variables are for locating the executable.

5 Answers 5

export VAR=value will set VAR to value. Enclose it in single quotes if you want spaces, like export VAR=’my val’ . If you want the variable to be interpolated, use double quotes, like export VAR=»$MY_OTHER_VAR» .

PS: no need for the double quotes in the last one. The shell does not perform word splitting for variable assignments.

Just for the beginners. I had not understood it directly, here in normal English: interpolate «$X» means here that you already have a variable X that is filled with a value, e.g. «A», and you want to read out that value «A» first, and then assign this value as the value of VAR. You do not want VAR to be a string of «$X» here of course. And then the comment above seems also logical, that you will not even need the «». And for a direct assignment of «A», use ‘A’. Please correct me if I got it wrong.

The reason people often suggest writing

is that the longer form works in more different shells than the short form. If you know you’re dealing with bash , either works fine, of course.

Set a local and environment variable using Bash on Linux

Check for a local or environment variables for a variable called LOL in Bash:

el@server /home/el $ set | grep LOL el@server /home/el $ el@server /home/el $ env | grep LOL el@server /home/el $ 

Sanity check, no local or environment variable called LOL.

Set a local variable called LOL in local, but not environment. So set it:

el@server /home/el $ LOL="so wow much code" el@server /home/el $ set | grep LOL LOL='so wow much code' el@server /home/el $ env | grep LOL el@server /home/el $ 

Variable ‘LOL’ exists in local variables, but not environment variables. LOL will disappear if you restart the terminal, logout/login or run exec bash .

Set a local variable, and then clear out all local variables in Bash

el@server /home/el $ LOL="so wow much code" el@server /home/el $ set | grep LOL LOL='so wow much code' el@server /home/el $ exec bash el@server /home/el $ set | grep LOL el@server /home/el $ 

You could also just unset the one variable:

el@server /home/el $ LOL="so wow much code" el@server /home/el $ set | grep LOL LOL='so wow much code' el@server /home/el $ unset LOL el@server /home/el $ set | grep LOL el@server /home/el $ 

Local variable LOL is gone.

Promote a local variable to an environment variable:

el@server /home/el $ DOGE="such variable" el@server /home/el $ export DOGE el@server /home/el $ set | grep DOGE DOGE='such variable' el@server /home/el $ env | grep DOGE DOGE=such variable 

Note that exporting makes it show up as both a local variable and an environment variable.

Exported variable DOGE above survives a Bash reset:

el@server /home/el $ exec bash el@server /home/el $ env | grep DOGE DOGE=such variable el@server /home/el $ set | grep DOGE DOGE='such variable' 

Unset all environment variables:

You have to pull out a can of Chuck Norris to reset all environment variables without a logout/login:

el@server /home/el $ export CAN="chuck norris" el@server /home/el $ env | grep CAN CAN=chuck norris el@server /home/el $ set | grep CAN CAN='chuck norris' el@server /home/el $ env -i bash el@server /home/el $ set | grep CAN el@server /home/el $ env | grep CAN 

You created an environment variable, and then reset the terminal to get rid of them.

Or you could set and unset an environment variable manually like this:

el@server /home/el $ export FOO="bar" el@server /home/el $ env | grep FOO FOO=bar el@server /home/el $ unset FOO el@server /home/el $ env | grep FOO el@server /home/el $ 

Источник

How to Set Environment Variables in Linux

In this tutorial, you will learn how to set environment variables in Ubuntu, CentOS, Red Hat, basically any Linux distribution for a single user and globally for all users. You will also learn how to list all environment variables and how to unset (clear) existing environment variables.

Environment variables are commonly used within the Bash shell. It is also a common means of configuring services and handling web application secrets.

It is not uncommon for environment specific information, such as endpoints and passwords, for example, to be stored as environment variables on a server. They are also used to set the important directory locations for many popular packages, such as JAVA_HOME for Java.

Setting an Environment Variable

To set an environment variable the export command is used. We give the variable a name, which is what is used to access it in shell scripts and configurations and then a value to hold whatever data is needed in the variable.

For example, to set the environment variable for the home directory of a manual OpenJDK 11 installation, we would use something similar to the following.

export JAVA_HOME=/opt/openjdk11

To output the value of the environment variable from the shell, we use the echo command and prepend the variable’s name with a dollar ($) sign.

And so long as the variable has a value it will be echoed out. If no value is set then an empty line will be displayed instead.

Unsetting an Environment Variable

To unset an environment variable, which removes its existence all together, we use the unset command. Simply replace the environment variable with an empty string will not remove it, and in most cases will likely cause problems with scripts or application expecting a valid value.

To following syntax is used to unset an environment variable

For example, to unset the JAVA_HOME environment variable, we would use the following command.

Listing All Set Environment Variables

To list all environment variables, we simply use the set command without any arguments.

An example of the output would look something similar to the following, which has been truncated for brevity.

BASH=/bin/bash BASHOPTS=checkwinsize:cmdhist:complete_fullquote:expand_aliases:extglob:extquote:force_fignore:globasciiranges:histappend:interactive_comments:login_shell:progcomp:promptvars:sourcepath BASH_ALIASES=() BASH_ARGC=([0]="0") BASH_ARGV=() BASH_CMDS=() BASH_COMPLETION_VERSINFO=([0]="2" [1]="8") BASH_LINENO=() BASH_SOURCE=() BASH_VERSINFO=([0]="5" [1]="0" [2]="3" [3]="1" [4]="release" [5]="x86_64-pc-linux-gnu") BASH_VERSION='5.0.3(1)-release' COLUMNS=208 DIRSTACK=() EUID=1000 GROUPS=() HISTCONTROL=ignoreboth HISTFILE=/home/ubuntu/.bash_history HISTFILESIZE=2000 HISTSIZE=1000 HOME=/home/ubuntu HOSTNAME=ubuntu1904 HOSTTYPE=x86_64 IFS=$' \t\n' LANG=en_US.UTF-8 LESSCLOSE='/usr/bin/lesspipe %s %s' LESSOPEN='| /usr/bin/lesspipe %s' LINES=54

Persisting Environment Variables for a User

When an environment variable is set from the shell using the export command, its existence ends when the user’s sessions ends. This is problematic when we need the variable to persist across sessions.

To make an environment persistent for a user’s environment, we export the variable from the user’s profile script.

Open the current user’s profile into a text editor

export JAVA_HOME=/opt/openjdk11

Adding the environment variable to a user’s bash profile alone will not export it automatically. However, the variable will be exported the next time the user logs in.

To immediately apply all changes to bash_profile, use the source command.

Export Environment Variable

Export is a built-in shell command for Bash that is used to export an environment variable to allow new child processes to inherit it.

To export a environment variable you run the export command while setting the variable.

export MYVAR="my variable value"

We can view a complete list of exported environment variables by running the export command without any arguments.

SHELL=/bin/zsh SHLVL=1 SSH_AUTH_SOCK=/private/tmp/com.apple.launchd.1pB5Pry8Id/Listeners TERM=xterm-256color TERM_PROGRAM=vscode TERM_PROGRAM_VERSION=1.48.2

To view all exported variables in the current shell you use the -p flag with export.

Setting Permanent Global Environment Variables for All Users

A permanent environment variable that persists after a reboot can be created by adding it to the default profile. This profile is loaded by all users on the system, including service accounts.

All global profile settings are stored under /etc/profile. And while this file can be edited directory, it is actually recommended to store global environment variables in a directory named /etc/profile.d, where you will find a list of files that are used to set environment variables for the entire system.

Create a new file under /etc/profile.d to store the global environment variable(s). The name of the should be contextual so others may understand its purpose. For demonstrations, we will create a permanent environment variable for HTTP_PROXY.

sudo touch /etc/profile.d/http_proxy.sh

sudo vi /etc/profile.d/http_proxy.sh

export HTTP_PROXY=http://my.proxy:8080

export HTTPS_PROXY=https://my.proxy:8080

export NO_PROXY=localhost. 1,.example.com

Conclusion

This tutorial covered how to set and unset environment variables for all Linux distributions, from Debian to Red Hat. You also learned how to set environment variables for a single user, as well as all users.

Источник

How to Set an Environment Variable in Linux

Zaira Hira

In programming, you use variables to store information like strings and numbers temporarily.

Variables can be used repeatedly throughout the code or by your operating system to provide values. You can edit them, overwrite them, and delete them.

In this tutorial, I’ll teach you what environment variables are and how to set them in Linux.

What Are Environment Variables?

Environment variables are the variables specific to a certain environment. For example, each user in an operating system has its own environment. An admin user has a different environment than other users do, for example.

You might declare an environment variable only required by your user (for example a secret token) that doesn’t need to be exposed to other users.

Here are some examples of environment variables in Linux:

• USER – This points to the currently logged-in user.
• HOME – This shows the home directory of the current user.
• SHELL – This stores the path of the current user’s shell, such as bash or zsh.
• LANG – This variable points to the current language/locales settings.
• MAIL – This shows the location of where the current user’s mail is stored.

These environment variables vary based on the current user session.

How to List Environment Variables in Linux

The command used to display all the environment variables defined for a current session is env .

Here is the output for my session:

For the changes to take effect, update the .bashrc file using the source command:

Let’s verify by opening a new session.

For the changes to take effect, use the command source /etc/environment .

• /etc/profile – Variables set in this file are read whenever a bash shell is logged in. Edit this file and use the export command:

Now, I’ll switch the user to the root user and verify if I can access the variable GLOBAL_VARIABLE .

root@Zaira:~# echo $GLOBAL_VARIABLE This is a global variable

It worked! I have been able to access the global variable defined by the user Zaira through the root user as well. The same would apply to other users too. So now you also know how to define global environment variables.

Conclusion

In this tutorial, you learned how to create and define environment variables in Linux. You also learned how to make them persistent so that you can use them across multiple sessions.

What’s your favorite thing you learned here? Let me know on Twitter!

You can read my other posts here.

Источник