Linux list all 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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Set and List Environment Variables in Linux

In Linux based systems you can set dynamic named values as environment variables. Those values are stored within the system and are used by command line applications. To put it simply, an environment variable is a variable with a name and an associated value. A variable is a symbol, letter, or a word such as «x» or «y,» that represents a value.

The environment variable can store information about the default text editor or browser, the path to executable files, etc.

An environment variable is globally available, in a program and its child programs. A shell variable is only available in the current shell.

In this tutorial, we will explain how to list and set the environment and shell variables.

Environment Variables

Environment variables are variables that are available system-wide and are inherited by all spawned child processes and shells.

The environment variables are implemented as strings that represent key-value pairs. If multiple values are passed, they are typically separated by colon (:) characters. Each pair will generally look something like this:

The names of the variables are case-sensitive and are usually used in an upper case format (MYVAR1, MYVAR2. )

If the value contains white-space, quotations are used:

Shell Variables

Shell variables are variables that are contained exclusively within the shell in which they were set or defined. Each shell such as zsh and bash, has its own set of internal shell variables. They are usually used to keep track of ephemeral data, like the current working directory. Usage is the same as with the global environment variables.

To make a shell variable available as an environment variable, use export MYVAR:

Common Environmental and Shell Variables

Some environmental and shell variables are very useful and are referenced fairly often. Here are some common environmental variables that you will come across:

TERM	This specifies the type of terminal to emulate when running the shell. Different hardware terminals can be emulated for different operating requirements. You usually won’t need to worry about this though.
USER	The current logged in user.
PWD	The current working directory.
OLDPWD	The previous working directory. This is kept by the shell in order to switch back to your previous directory by running cd -.
LS_COLORS	This defines color codes that are used to optionally add colored output to the ls command. This is used to distinguish different file types and provide more info to the user at a glance.
MAIL	The path to the current user’s mailbox.
PATH	A list of directories that the system will check when looking for commands. When a user types in a command, the system will check directories in this order for the executable.
LANG	The current language and localization settings, including character encoding.
HOME	The current user’s home directory.
_	The most recent previously executed command.

In addition to these environmental variables, some shell variables that you’ll often see are:

BASHOPTS	The list of options that were used when bash was executed. This can be useful for finding out if the shell environment will operate in the way you want it to.
BASH_VERSION	The version of bash being executed, in human-readable form.
BASH_VERSINFO	The version of bash, in machine-readable output.
COLUMNS	The number of columns wide that are being used to draw output on the screen.
DIRSTACK	The stack of directories that are available with the pushd and popd commands.
HISTFILESIZE	Number of lines of command history stored to a file.
HISTSIZE	Number of lines of command history allowed in memory.
HOSTNAME	The hostname of the computer at this time.
IFS	The internal field separator to separate input on the command line. By default, this is a space.
PS1	The primary command prompt definition. This is used to define what your prompt looks like when you start a shell session. The PS2 is used to declare secondary prompts for when a command spans multiple lines.
SHELLOPTS	Shell options that can be set with the set option.
UID	The UID of the current user.

List Shell and Environment Variables

There are several commands available that allow you to list environment variables in Linux:

env – The command 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 – The command prints all or the specified environment variables.
set – The command sets or unsets shell variables. When used without an argument it will print a list of all variables including environment and shell variables, and shell functions.

In their default state, env and printenv should function exactly the same:

The difference between env and ‘printenv’ commands is only apparent in their more specific functionality. For instance, with ‘printenv’, you can request the values of individual variables:

env command lets you modify the environment in which programs are running, by passing a set of variables into a command:

The printenv and env commands print only the environment variables. If you want to get a list of all variables, including environment and shell variables, and shell functions you can use the set command:

The command will display a large list of all variables so you probably want to pipe the output to the less command.

Set Shell and Environment Variables

Commands available to set environment variables in Linux are:

set – The command sets or unsets shell variables. When used without an argument it will print a list of all variables including environment and shell variables, and shell functions.
unset – The command deletes shell and environment variables.
export – The command sets environment variables.

To better understand the difference between shell and environmental variables we’ll start with setting shell variables and then move on to the environment variables.

We will begin by defining a shell variable within our current session. You can verify that the variable is set by using echo $MYVAR

Use the printenv command to check whether this variable is an environment variable or not:

No output should be returned. This means that MYVAR variable is not an environment variable.

The export command is used to set Environment variables.

To create an environment variable simply export the shell variable as an environment variable:

You can check this by running:

You can also set environment variables in a single line:

Environment variables created this way are available only for the current session. If you open a new shell, or if you log out, all variables will be lost.

We can also revert an environment variable to shell variable, or even completely (unset) remove it:

Our MYVAR variable is defined as an environmental variable. We can change it back into a shell variable by typing:

It is no longer an environmental variable, however, it is still a shell variable.

If we want to completely unset a variable, either shell or environmental, we can do so with the unset command:

We can verify that it is no longer set:

Nothing is returned because the variable has been unset.

Persistent Environment Variables

We’ve already mentioned that many programs use environmental variables to decide the specifics of how to operate. We do not want to have to set important variables up every time we start a new shell session,
The bash shell reads different configuration files depending on how the session is started.
An interactive shell session is a shell session that is attached to a terminal. A non-interactive shell session is one is not attached to a terminal session.

One distinction between different sessions is whether the shell is being spawned as a “login” or “non-login” session.

In most Linux distributions when you start a new session, environment variables are read from the following files:

/etc/environment — Use this file to set up system-wide environment variables.

/etc/profile — Variables set in this file are loaded whenever a bash login shell is entered.

/.bashrc — Per-user shell specific configuration files. For example, if you are using Bash, you can declare the variables there.

To load the new environment variables into the current shell session use the source command:

If you need to set system-wide variables, you may want to think about adding them to /etc/profile, /etc/bash.bashrc, or /etc/environment.

Conclusion

In this tutorial, we have learned how to set and list environment and shell variables. These variables are always present in your shell sessions and can be very useful for many programs. There are plenty of other, more mundane, but more common scenarios where you will need to read or alter the environment of your system. If you have any questions, please feel free to leave them in the comments below.

The command will display a large list of all variables so you probably want to pipe the output to the less command.

Set Shell and Environment Variables

Commands available to set environment variables in Linux are:

set – The command sets or unsets shell variables. When used without an argument it will print a list of all variables including environment and shell variables, and shell functions.
unset – The command deletes shell and environment variables.
export – The command sets environment variables.

To better understand the difference between shell and environmental variables we’ll start with setting shell variables and then move on to the environment variables.

We will begin by defining a shell variable within our current session. You can verify that the variable is set by using echo $MYVAR

Use the printenv command to check whether this variable is an environment variable or not:

No output should be returned. This means that MYVAR variable is not an environment variable.

The export command is used to set Environment variables.

To create an environment variable simply export the shell variable as an environment variable:

You can check this by running:

You can also set environment variables in a single line:

Environment variables created this way are available only for the current session. If you open a new shell, or if you log out, all variables will be lost.

We can also revert an environment variable to shell variable, or even completely (unset) remove it:

Our MYVAR variable is defined as an environmental variable. We can change it back into a shell variable by typing:

It is no longer an environmental variable, however, it is still a shell variable.

If we want to completely unset a variable, either shell or environmental, we can do so with the unset command:

We can verify that it is no longer set:

Nothing is returned because the variable has been unset.

Persistent Environment Variables

We’ve already mentioned that many programs use environmental variables to decide the specifics of how to operate. We do not want to have to set important variables up every time we start a new shell session,
The bash shell reads different configuration files depending on how the session is started.
An interactive shell session is a shell session that is attached to a terminal. A non-interactive shell session is one is not attached to a terminal session.

One distinction between different sessions is whether the shell is being spawned as a “login” or “non-login” session.

In most Linux distributions when you start a new session, environment variables are read from the following files:

/etc/environment — Use this file to set up system-wide environment variables.

/etc/profile — Variables set in this file are loaded whenever a bash login shell is entered.

/.bashrc — Per-user shell specific configuration files. For example, if you are using Bash, you can declare the variables there.

To load the new environment variables into the current shell session use the source command:

If you need to set system-wide variables, you may want to think about adding them to /etc/profile, /etc/bash.bashrc, or /etc/environment.

Conclusion

In this tutorial, we have learned how to set and list environment and shell variables. These variables are always present in your shell sessions and can be very useful for many programs. There are plenty of other, more mundane, but more common scenarios where you will need to read or alter the environment of your system. If you have any questions, please feel free to leave them in the comments below.

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