Bash 3.0 not supporting lists?

Question

I have written a small script that add particular IP addresses taken from a config file and then puts it in a list :

  WAS_IP=$(grep "<was_ip>" $CONFIG| cut -d '>' -f 2 | cut -d '<' -f 1 | xargs)

  NODES=()
  NODES+=("$WAS_IP")

On bash 3.2.25this works fine but on 3.0 where I have my production environment this gives an error :

./config.sh: line 3154: syntax error near unexpected token `"$WAS_IP"'
./config.sh: line 3154: `      NODES+=("$WAS_IP")'

How can I avoid this issue ?

Answer 1

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.