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

You should specify the variable with the following syntax:

MYVAR=74 ./myscript.sh

Within the script, check if it is already set before setting it:

if [ ! -z $MYVAR ]; then
    #do something
fi