Test if element is in array in bash

In Bash 4, you can use associative arrays:

# set up array of constants
declare -A array
for constant in foo bar baz
do
    array[$constant]=1
done

# test for existence
test1="bar"
test2="xyzzy"

if [[ ${array[$test1]} ]]; then echo "Exists"; fi    # Exists
if [[ ${array[$test2]} ]]; then echo "Exists"; fi    # doesn't

To set up the array initially you could also do direct assignments:

array[foo]=1
array[bar]=1
# etc.

or this way:

array=([foo]=1 [bar]=1 [baz]=1)

It's an old question, but I think what is the simplest solution has not appeared yet: test ${array[key]+_}. Example:

declare -A xs=([a]=1 [b]="")
test ${xs[a]+_} && echo "a is set"
test ${xs[b]+_} && echo "b is set"
test ${xs[c]+_} && echo "c is set"

Outputs:

a is set
b is set

To see how this work check this.

There is a way to test if an element of an associative array exists (not set), this is different from empty:

isNotSet() {
    if [[ ! ${!1} && ${!1-_} ]]
    then
        return 1
    fi
}

Then use it:

declare -A assoc
KEY="key"
isNotSet assoc[${KEY}]
if [ $? -ne 0 ]
then
  echo "${KEY} is not set."
fi