Linux Environment Variables

Environment Variables¶

The names of variables are case sensitive.
By convention environment variables have upper case names.
When assigning multiple values to the variable they must be separated by the colon : character.
There is no space around the equals = symbol.
Variables can be classified into two main categories,
- Environment variables: are variables that are available system-wide and are inherited by all spawned child processes and shells.
- Shell variables: are variables that apply only to the current shell instance.

Some commands¶

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.
unset → The command deletes shell and environment variables.
export → The command sets environment variables.

Print a specific environment variable¶

printenv NAME

echo $NAME

The echo command can print environment and shell variables whereas printenv can only print environment variables.

Setting shell variables¶

TEST_VARIABLE='value'

We can display it using echo. If we do

printenv | grep TEST_VARIABLE

We will get no output since it is not an environment variable.
If you close the shell the variable will be deleted.

Setting environment variables¶

export TEST_VARIABLE='value'

If you close the shell the environment variable will be lost.
One of the most common use of the export command is when you want to add something to the path so that your Linux system will find the certain command/executable file.
- What does it do? It adds this directory location to the path. When you try to run a command in Linux, your system searches for its executable (usually in bin directory) in the directories mentioned in the PATH variable.

Creating persistent environment variables¶

Different ways of creating persistent environment variables:

Use of `export`¶

export makes the variable available to sub-processes.

export name=value

- This means that the variable name is available to any process you run from that shell process. - If you want a process to make use of this variable, use export, and run the process from that shell.

name=value

The above means the variable scope is restricted to the shell, and is NOT available to any other process.
You would use this for (say) loop variables, temporary variables etc.

Exporting a variable DOESN'T make it available to parent processes.

That is, specifying and exporting a variable in a spawned process doesn't make it available in the process that launched it.

Example

Last updated: 2023-05-15