What does export variable without an equals sign do?

Question

There's a bash script on my linux machine with these two lines:

[ -r /etc/java/java.conf ] && . /etc/java/java.conf
export JAVA_HOME

What does the export JAVA_HOME do? Usually I thought export VARIABLE_NAME=something sets the variable to something.

What does running export JAVA_HOME without setting it to something do?

I tried running it on the commandline, but nothing happens.

Answer 1

The two lines of code (better to use double brackets):

[[ -r /etc/java/java.conf ]] && . /etc/java/java.conf
export JAVA_HOME

...equates to this:

-r checks if /etc/java/java.conf exists and read permission is granted.

&& if the condition above is true then source the file.

export JAVA_HOME takes the previously-assigned value of $JAVA_HOME from the sourced file making it available to subprocesses rather than only within the shell.

• What does "export" do in shell programming?
• What does "source" do?
• Conditional statements in bash