[SOLVED] Shell script - loop in batches

Issue

I have a sample script like below, where I pass the server names as comma separated stings and execute the functions for each server. Now I need to execute this in batches, e.g. in first batch functions will call with a,b,c,d. Once finished they will take next 4 and call the functions and at last they will call last 2. I can't change the 'servers' variable. Any ides/suggestions.

servers = a,b,c,d,e,f,g,h,i,j
OIFS=$IFS;
IFS=",";
for server in ${servers}
do
 function1 server
done
for server in ${servers}
do
 function2 server
done
for server in ${servers}
do
 function3 server
done
IFS=$OIFS;

Please note that server variable length is not fixed and based on the environment it loads different servers.

Solution

Read the server list into an array, then use substring expansion (aka "slicing"). You can also store the names of the functions to call in an array, if I (now) understand your concern over the size of the list of servers.

IFS=, read -a s <<< "$servers"

bs=4  # batch size
for ((i=0; i<=${#s[@]}; i+=bs)); do
    function1 "${s[@]:i:bs}"
    function2 "${s[@]:i:bs}"
    function3 "${s[@]:i:bs}"
done

Answered By - chepner