an example to use commas as delimiters for 'for' in bash.

comma_for_deliter_tech.sh

#!/bin/bash

CMD_LINE="ro root=/dev/example1,/dev/example2 splash quiet"

for CMD_PARAM in ${CMD_LINE}; do
    case ${CMD_PARAM} in
        root=*)
            ROOT_DEV=${CMD_PARAM#root=}
            ;;
        *)
            echo "parameters other than 'root': ${CMD_PARAM}"
            ;;
    esac
done

echo "==== ROOT_DEV ===="
echo ${ROOT_DEV}
echo "==== DEVICES ===="

################ TECH HERE ################
# replace comma with space to split
for DEV in ${ROOT_DEV//,/ }; do
    echo ${DEV}
done