Linux commands environment variables

Linux List All Environment Variables Command

1. printenv command – Print all or part of environment.
2. env command – Display all exported environment or run a program in a modified environment.
3. set command – List the name and value of each shell variable.

Tutorial details
Difficulty level	Easy
Root privileges	No
Requirements	Linux or Unix
Est. reading time	4 mintues

Linux list all environment variables command

I recommend that you use the printenv command. The syntax is:

Fig.01: Command to see a list of all currently defined environment variables in a Linux bash terminal

A list of the commonly used variables in Linux

We use the printf command/echo command to display values of the shell varible in Linux.

System Variable	Meaning	To view variable value type
BASH_VERSION	Holds the version of this instance of bash.	echo $BASH_VERSION
HOSTNAME	The name of the your computer.	echo $HOSTNAME
CDPATH	The search path for the cd command.	echo $CDPATH
HISTFILE	The name of the file in which command history is saved.	echo $HISTFILE
HISTFILESIZE	The maximum number of lines contained in the history file.	echo $HISTFILESIZE
HISTSIZE	The number of commands to remember in the command history. The default value is 500.	echo $HISTSIZE
HOME	The home directory of the current user.	echo $HOME
IFS	The Internal Field Separator that is used for word splitting after expansion and to split lines into words with the read builtin command. The default value is .	echo $IFS
LANG	Used to determine the locale category for any category not specifically selected with a variable starting with LC_.	echo $LANG
PATH	The search path for commands. It is a colon-separated list of directories in which the shell looks for commands.	echo $PATH
PS1	Your prompt settings.	echo $PS1
TMOUT	The default timeout for the read builtin command. Also in an interactive shell, the value is interpreted as the number of seconds to wait for input after issuing the command. If not input provided it will logou user.	echo $TMOUT
TERM	Your login terminal type.	echo $TERM export TERM=vt100
SHELL	Set path to login shell.	echo $SHELL
DISPLAY	Set X display name	echo $DISPLAY export DISPLAY=:0.1
EDITOR	Set name of default text editor.	export EDITOR=/usr/bin/vim

set and env command

You can use the env / set command too:

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A note about env/set command

The env will only display a list of environment variables that have been exported and it will not show all bash variables. The set command allows you to change the values of shell options and set the positional parameters, or to display the names and values of shell variables. If no options or arguments are supplied, set displays the names and values of all shell variables and functions, sorted according to the current locale, in a format that may be reused as input for setting or resetting the currently-set variables. Hence, I recommend that you use printenv command to dump the list of all shell variables on screen. To save the list of all shell environment variables to a file, enter:

Use the grep command to search for particular variable:

Conclusion

You learned about listing all Linux shell environment variables. See the following resources for more information:

• Bash shell variables from the Linux shell scripting wiki.
• See the following man pages using the man command or help command:
  man ‘printenv(1)’
  man 1 bash
  man 1 env

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Comments on this entry are closed.

Thank you aref ghobadi Aug 18, 2015 @ 8:33

Thank you for this useful information.

Thank you.It’s really helpful.

Thank you. This is a very informative.

Note that set will show all unexported shell variables (e.g. like PS1 , TMOUT ) whereas env or printenv will not.

Thanks for the input 🙂

With environment variables, what’s the maximum amount of characters a environment variable can have?
and is it possible to set this higher?

The theoretical max length of an environment variable is around 32,760 characters. The maximum size of an environment variable value depends upon execve(). Try:
false | xargs —show-limits
Which gives out:

On my box it went up to 512MiB and failed with the following message (see image here)[1]:

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How To – Linux Set Environment Variables Command

1. Configure look and feel of shell.
2. Setup terminal settings depending on which terminal you’re using.
3. Set the search path such as JAVA_HOME, and ORACLE_HOME.
4. Create environment variables as needed by programs.
5. Run commands that you want to run whenever you log in or log out.
6. Set up aliases and/or shell function to automate tasks to save typing and time.
7. Changing bash prompt.
8. Setting shell options.

Tutorial details
Difficulty level	Easy
Root privileges	No
Requirements	Linux
Est. reading time	11 minutes

Two types of shell variables

• Environment variables (GLOBAL): Typically, end-users shouldn’t mess with Environment variables as they are available system-wide, and subshells and child processes can access them. In certain scenarios, we can modify them as per our needs. For example, we set up a system-wide path for the JAVA app or PATH for searching binaries. In almost all cases, we use the export command to define or modify environment variables.
• Shell and user-defined variables (LOCAL) : As the name suggests, these are defined by users and currently apply to the current shell session.

You can use the following commands to view and configure the environment.

Display current environment variables on Linux

The printenv command shows all or the given environment variables. Open the terminal prompt and then type:
printenv
printenv VAR_NAME
printenv PS1
printenv ORACLE_HOME
printenv JAVA_HOME
# use the grep command/egrep command to filter out variables #
printenv | grep APP_HOME
printenv | egrep ‘APP_HOME|DOCKER_HOME|NIX_BACKUP_HOST’

env command

The env command runs a Linux command with a modified environment. The syntax is:

Please note that If no command name is specified following the environment specifications, the resulting environment is displayed on screen. This is like specifying the printenv command as discussed earlier. For example:

How to set and list environment variables in Linux using set command

The env command/printenv command displays only the Linux shell environment variables. What if you need to see a list of all variables, including shell, environment, user-defined shell functions? Try the following set command for printing environment variables:
set
set | grep BASH
Here is what we see:

The $PATH defined the search path for commands. It is a colon-separated list of directories in which the shell looks for commands. The $PS1 defines your prompt settings. See the list of all commonly used shell variables for more information. You can display the value of a variable using the printf command or echo command:

Outputs from the last command displaying my home directory location set by the $HOME environment variable on Linux:
/home/vivek

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Linux environment variable tips and tricks

Environment variables exist to enhance and to standardize your shell environment on Linux systems. There are standard environment variables that the system sets up for you, but you can also set up your own environment variables, or optionally change the default ones to meet your needs.

Starting with the env command

If you want to see your environment variables, use the env command and look for the words in all caps in the output’s far left. These are your environment variables, and their values are to the right:

More Linux resources

I have omitted the output of the LS_COLORS variable because it is so long. Try this command on your system to see what the full output looks like.

Many environment variables are set and then exported from the /etc/profile file and the /etc/bashrc file. There is a line in /etc/profile that reads:

To make permanent changes to the environment variables for all new accounts, go to your /etc/skel files, such as .bashrc , and change the ones that are already there or enter the new ones. When you create new users, these /etc/skel files will be copied to the new user’s home directory.

Exploring shell levels ( SHLVL )

To call the value of a single environment variable, enter the following command, using SHLVL (Shell Level) as an example:

This variable changes depending on how many subshells you have open. For example, enter bash twice and then issue the command again:

A shell level of three means that you are two subshells deep, so type exit twice to return to your regular shell.

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Manipulating your PATH variable

The PATH variable contains the search path for executing commands and scripts. To see your PATH , enter:

Temporarily change your PATH by entering the following command to add /opt/bin :

The change is temporary for the current session. It isn’t permanent because it’s not entered into the .bashrc file. To make the change permanent, enter the command PATH=$PATH:/opt/bin into your home directory’s .bashrc file.

When you do this, you’re creating a new PATH variable by appending a directory to the current PATH variable, $PATH . A colon ( : ) separates PATH entries.

Unraveling $USER , $PWD , and $LOGNAME

I had a theory that I think has been dispelled by my own good self. My theory was that the commands pwd and whoami probably just read and echoed the contents of the shell variables $PWD and $USER or $LOGNAME , respectively. To my surprise, after looking at the source code, they don’t. Maybe I should rewrite them to do just that. There’s no reason to add multiple libraries and almost 400 lines of C code to display the working directory. You can just read $PWD and echo that to the screen (stdout). The same goes for whoami with either $USER or $LOGNAME .

If you want to have a look at the source code for yourself, it’s on GitHub and other places. If you find that these programs (or others) do use shell variables, I’d love to know about it. Admittedly, I’m not that great at reading C source code, so they could very well use shell variables and I’d never know it. They just didn’t seem to from what I read and could understand.

Playing the $SHELL game

In this last environment variable overview, I want to show you how the $SHELL variable comes in handy. You don’t have to stay in your default shell, which is likely Bash. You can enter into and work in any shell that’s installed on the system. To find out which shells are installed on your system, use the following command:

All of those are actually Bash, so don’t get excited. If you’re lucky, you might also see entries for /bin/tcsh , /bin/csh , /bin/mksh , /bin/ksh , and /bin/rksh .

You can use any of these shells and have different things going on in each one if you’re so inclined. But, let’s say that you’re a Solaris admin and you want to use the Korn shell. You can change your default shell to /bin/ksh using the chsh command:

Now, if you type echo $SHELL , the response will be /bin/bash , so you have to log out and log in again to see the change. Once you log out and log in, you will receive a different response to echo $SHELL .

You can enter other shells and echo $SHELL should report your current shell and $SHLVL , which will keep you oriented as to how many shells deep you are.

Setting your own environment variables

You can set your own variables at the command line per session, or make them permanent by placing them into the

/.profile , or whichever startup file you use for your default shell. On the command line, enter your environment variable and its value as you did earlier when changing the PATH variable.

Wrapping up

Shell or environment variables are helpful to users, sysadmins, and programmers alike. They are useful on the command line and in scripts. I’ve used them over the years for many different purposes, and although some of them are probably a little unconventional, they worked and still do. Create your own or use the ones given to you by the system and installed applications. They truly can enrich your Linux user experience.

As a side note on variables and shells, does anyone think that those who program in JSON should only be allowed to use the Bourne Shell? Discuss.

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