Ternary operator (?:) in Bash

ternary operator ? : is just short form of if/else

case "$b" in
 5) a=$c ;;
 *) a=$d ;;
esac

Or

 [[ $b = 5 ]] && a="$c" || a="$d"

Code:

a=$([ "$b" == 5 ] && echo "$c" || echo "$d")