Linux commands: export

The export command is used to export variables to child processes.

What does this mean?

Suppose you have a variable TEST defined in this way:

TEST="test"

You can print its value using echo $TEST:

But if you try defining a Bash script in a file script.sh with the above command:

Then you set chmod u+x script.sh and you execute this script with ./script.sh, the echo $TEST line will print nothing!

This is because in Bash the TEST variable was defined local to the shell. Running ./script.sh starts a new child process (a new shell). That shell only receives the exported variables, the environment.

To make the variable available there we need to define TEST not in this way:

TEST="test"

but in this way:

export TEST="test"

Try that, and running ./script.sh now should print “test”:

Sometimes you need to append something to a variable. It’s often done with the PATH variable. You use this syntax:

export PATH=$PATH:/new/path

It’s common to use export when you create new variables in this way, but also when you create variables in the .bash_profile or .bashrc configuration files with Bash, or in .zshenv with Zsh.

In Bash, export -n TEST only removes the export flag. The variable still exists in the current shell. Child processes stop seeing it.

export -n TEST

To remove the variable, use unset:

unset TEST

zsh, the macOS default shell, does not support export -n. Use typeset +x TEST there.

See how to set environment variables in bash and zsh. env runs a command with a custom environment.

Calling export without any option will list all the exported variables.

The export command works on Linux, macOS, WSL, and anywhere you have a UNIX environment

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