How do I do if statement arithmetic in bash?

Question

I want to do something like this:

if [ $1 % 4 == 0 ]; then
...

But this does not work.

What do I need to do instead?

Answer 1

single brackets ([..]) don't work for some tests, try with double brackets ([[...]]) and enclose the mod in ((..)) to evaluate the % operator properly:

if [[ $(( $1 % 4 )) == 0 ]]; then

More details here:
http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_02.html