Circular iteration in bash

Question

I'd have a couple of possible (say string) values: a b c. I'd like a to switch from one to another in a circular way:

if [ "$value" == "a" ]; then value=b
elif [ "$value" == "b"]; then value=c
elif [ "$value" == "c"]; then value=a
fi

With method like this, Can this be done in a more efficient way, so that I could support many options, like a b c ... z?

Answer 1

It can be done like this:

get_next()
{
    __current_i=${__current_i:- 0} # global variable that saves index of current value
    [ $__current_i -ge $# ] && __current_i=0 # if we exceed the number of values, then reset to zero
    shift $__current_i # move to current value
    ((__current_i++)) # increment index
    echo $1
}

val="a b c d"

get_next $val
get_next $val
get_next $val
get_next $val
get_next $val