A bash function to check if an item is duplicated in a list. That is to say, it checks to make sure it is not already in the list.

not_duplicated.sh

#!/bin/bash

# A function that checks if an item is not already in a list.
# The first argument is the item to check for, the rest are the list to check in.
# Returns 1 if the item is duplicated in the list, or 0 if it's not.
not_duplicated() {

    # The first argument is the item to check for.
    local ITEM=$1

    # The rest are the list to check in.
    local LIST="${@:2}"

    # If we find the item in the list, return 1.
    for I in ${LIST[@]}
    do 
        if [[ $I == $ITEM ]]; then
            return 1
        fi
    done

    # Otherwise, we're good.
    return 0

}