7.2.1.2. Exporting variables

An individual variable's content is usually displayed using the echo command, as in these examples:

debby:~> echo $PATH
/usr/bin:/usr/sbin:/bin:/sbin:/usr/X11R6/bin:/usr/local/bin

debby:~> echo $MANPATH
/usr/man:/usr/share/man/:/usr/local/man:/usr/X11R6/man

If you want to change the content of a variable in a way that is useful to other programs, you have to export the new value from your environment into the environment that runs these programs. A common example is exporting the PATH variable. You may declare it as follows, in order to be able to play with the flight simulator software that is in /opt/FlightGear/bin:

debby:~> PATH=$PATH:/opt/FlightGear/bin

This instructs the shell to not only search programs in the current path, $PATH, but also in the additional directory /opt/FlightGear/bin.

However, as long as the new value of the PATH variable is not known to the environment, things will still not work:

debby:~> runfgfs
bash: runfgfs: command not found

Exporting variables is done using the shell built-in command export:

debby:~> export PATH

debby:~> runfgfs
--flight simulator starts--

In Bash, we normally do this in one elegant step:

export VARIABLE=value

The same technique is used for the MANPATH variable, that tells the man command where to look for compressed man pages. If new software is added to the system in new or unusual directories, the documentation for it will probably also be in an unusual directory. If you want to read the man pages for the new software, extend the MANPATH variable:

debby:~> export MANPATH=$MANPATH:/opt/FlightGear/man

debby:~> echo $MANPATH
/usr/man:/usr/share/man:/usr/local/man:/usr/X11R6/man:/opt/FlightGear/man

You can avoid retyping this command in every window you open by adding it to one of your shell setup files, see Section 7.2.2.