The export command is used to set environment variables in a Linux or Unix shell. Environment variables are variables that are set in the shell and are available to all processes that are started from the shell.
To set an environment variable, you can use the export command followed by the variable name and value. For example, to set the FOO variable to bar, you can use the following command:
export FOO=bar
This will set the FOO variable to bar for the current shell session. To make the change permanent, you can add the export line to your Bash profile file, such as ~/.bashrc or ~/.bash_profile.
You can also set multiple variables at once by separating them with a space. For example:
export FOO=bar BAZ=qux
This will set the FOO variable to bar and the BAZ variable to qux.
To view the current value of an environment variable, you can use the echo command. For example:
echo $FOO
This will print the value of the FOO variable to the console.
To unset an environment variable, you can use the unset command followed by the variable name. For example:
unset FOO
This will unset the FOO variable and remove it from the environment.
Keep in mind that environment variables are specific to the shell and are not inherited by child processes. If you want to set an environment variable for a child process, you can use the env command to set the variable in the child process's environment.
For example, to start a new shell with the FOO variable set to bar, you can use the following command:
env FOO=bar bash
This will start a new Bash shell with the FOO variable set to bar. The FOO variable will not be set in the parent shell.