Override a variable in a Bash script from the command line

Question

How do you override a variable in your Bash script from the command line?

I know how to pass variables in, but I just want something like ./myscript.sh -Dvar=v

Answer 1

I would do it like this:

# if JAVA_HOME not set, then set with default value
if [ "x$JAVA_HOME" = "x" ]; then
    JAVA_HOME=/opt/java
fi