Check if a Bash array contains a value

Question

In Bash, what is the simplest way to test if an array contains a certain value?

Answer 1

If you need performance, you don't want to loop over your whole array every time you search.

In this case, you can create an associative array (hash table, or dictionary) that represents an index of that array. I.e. it maps each array element into its index in the array:

make_index () {
  local index_name=$1
  shift
  local -a value_array=("$@")
  local i
  # -A means associative array, -g means create a global variable:
  declare -g -A ${index_name}
  for i in "${!value_array[@]}"; do
    eval ${index_name}["${value_array[$i]}"]=$i
  done
}

Then you can use it like this:

myarray=('a a' 'b b' 'c c')
make_index myarray_index "${myarray[@]}"

And test membership like so:

member="b b"
# the "|| echo NOT FOUND" below is needed if you're using "set -e"
test "${myarray_index[$member]}" && echo FOUND || echo NOT FOUND

Or also:

if [ "${myarray_index[$member]}" ]; then 
  echo FOUND
fi

Notice that this solution does the right thing even if the there are spaces in the tested value or in the array values.

As a bonus, you also get the index of the value within the array with:

echo "<< ${myarray_index[$member]} >> is the index of $member"