The += operator appeared in Bash version 3.1.

• In older versions you can either assign to the element after array's last element:

    NODES[${#NODES[@]}]="$WAS_IP"
  

  If you append new values in one certain place, you may use a separate counter variable:

    NODES=()
    NODES_length=0
    NODES[NODES_length++]="$WAS_IP"
  

  But this is just moderately faster than asking the array's length with ${#NODES[@]}.

• Or you can assign the whole array to the existing elements and the new one:

    NODES=("${NODES[@]}" "$WAS_IP")
  

  Needless to say, better avoid this later one.

The += operator appeared in Bash version 3.1.

• In older versions, if the array is not sparse, you can either assign to the element after the array's last element:

    NODES[${#NODES[@]}]="$WAS_IP"
  

  If you append new values in one certain place, you may use a separate counter variable:

    NODES=()
    NODES_length=0
    NODES[NODES_length++]="$WAS_IP"
  

  But this is just moderately faster than asking the array's length with ${#NODES[@]}.

• Or you can assign the whole array to the existing elements and the new one:

    NODES=("${NODES[@]}" "$WAS_IP")
  

  Needless to say, better avoid this latter one. If the array was initially sparse, the array indices will have changed after that assignment.

The += operator appeared in Bash version 3.1.

In older versions you can either assign to the element after array's last element:

NODES[${#NODES[@]}]="$WAS_IP"

Or assign the whole array to the existing elements and the new one:

NODES=("${NODES[@]}" "$WAS_IP")

Needless to say, better avoid the later one.

The += operator appeared in Bash version 3.1.

• In older versions you can either assign to the element after array's last element:

    NODES[${#NODES[@]}]="$WAS_IP"
  

  If you append new values in one certain place, you may use a separate counter variable:

    NODES=()
    NODES_length=0
    NODES[NODES_length++]="$WAS_IP"
  

  But this is just moderately faster than asking the array's length with ${#NODES[@]}.

• Or you can assign the whole array to the existing elements and the new one:

    NODES=("${NODES[@]}" "$WAS_IP")
  

  Needless to say, better avoid this later one.