Bash assign variable command output depending on index loop

Question

I have something like this:

#!/bin/bash

#numero di nodi cache della edge network
NCACHES=$1

#creo vm manager (dello swarm) e balancer
docker-machine create -d virtualbox manager
docker-machine create -d virtualbox balancer

#creo le restanti NCACHES-1 VM
for i in {0..NCACHES-1}
do 
    echo "Creating VM $i"
    docker-machine create -d virtualbox worker$i
done

docker-machine create -d virtualbox backend

IPManager="$(docker-machine ip manager)"
echo "IP VM swarm manager=$IPManager"

IPBalancer="$(docker-machine ip balancer)"
echo "IP VM balancer=$IPBalancer"

for i in {0..NCACHES-1}}
do
    IPCache$i="$(docker-machine ip worker$i)"
    echo "IP worker$i=IPCache$i"
done

I want that in the last loop, i don't know how to pass i index to the "$(docker-machine ip worker$i)" command, and then set IPCache$i to this returned value. Then i don't know how to echo all these IP addresses.

Why don't you make IPCache an array? Then you can have just one IPCache variable and set `IPCache[$i]` — Charles Duffy, May 31 '17 at 13:04
You're looking for [variable indirection](http://tldp.org/LDP/abs/html/ivr.html), but I second Charles Duffy's suggestion to use an array instead — Aaron, May 31 '17 at 13:04
`for i in {0..NCACHES-1}` will never work! brace expansion will happen _before_ variable expansion — Inian, May 31 '17 at 13:05
@Aaron, *grumble* re: suggesting the ABS as a reference -- it's the W3Schools of bash, full of outdated information and bad-practice examples. I'd strongly suggest [the BashFAQ #6 section on indirect assignment](http://mywiki.wooledge.org/BashFAQ/006#Assigning_indirect.2Freference_variables) instead. — Charles Duffy, May 31 '17 at 13:05
@CharlesDuffy thanks for the info, I'll take care to avoid linking to this site from now on — Aaron, May 31 '17 at 13:08

John Kugelman · Accepted Answer · 2017-05-31T13:52:53.210

1

Use an array.

IPCache=()

for ((i = 0; i < NCACHES; i++))
do
    IPCache+=("$(docker-machine ip worker$i)")
    echo "IP worker$i=${IPCache[i]}"
done

edited May 31 '17 at 13:52

answered May 31 '17 at 13:05

John Kugelman

349,597
67
533
578

Bash assign variable command output depending on index loop

1 Answers1