Easiest way to check for an index or a key in an array?

Question

Using:

set -o nounset

1. Having an indexed array like:

   myArray=( "red" "black" "blue" )
            
   
   
           

Answer 1

To check if the element is set (applies to both indexed and associative array)

[ ${array[key]+abc} ] && echo "exists"

Basically what ${array[key]+abc} does is

• if array[key] is set, return abc
• if array[key] is not set, return nothing

---

References:

1. See Parameter Expansion in Bash manual and the little note

   if the colon is omitted, the operator tests only for existence [of parameter]

2. This answer is actually adapted from the answers for this SO question: How to tell if a string is not defined in a bash shell script?

---

A wrapper function:

exists(){
  if [ "$2" != in ]; then
    echo "Incorrect usage."
    echo "Correct usage: exists {key} in {array}"
    return
  fi   
  eval '[ ${'$3'[$1]+muahaha} ]'  
}

For example

if ! exists key in array; then echo "No such array element"; fi