Remote SSH commands with for loop

Question

I'm running running ssh commands from client machine on a remote machine:

ssh  -o "StrictHostKeyChecking no" -i $key 'user'@$public_ip "    
i=1;
workerips: "ip1 ip2";
for ip in $worker_ips; do
    echo \"ipis: ${ip} and i is ${i}\"
done;"

My problem is that '$ip' and '$i' are empty inside the 'for' loop. '$i' keeps its value outside the for loop. What am I doing wrong?

should the 3rd line not read workips="ip1 ip2";? Actually, you probably need to escape those quotes: workerips=\"ip1 ip2\";. You probably also need to escape each $ to \$ so that it's interpreted on the remote machine rather than locally. — joanis
– joanis, Commented Jul 3, 2019 at 22:27
thanks escaping $ to \$ fixed it. I already had the 3rd line with escape quotes in code, didn't include that in the question. — codebee
– codebee, Commented Jul 3, 2019 at 22:34

William Pursell · Accepted Answer · 2019-07-03 22:51:11Z

3

It's a lot easier to do this sort of thing with a heredoc:

$ ssh -o "StrictHostKeyChecking no" -i "$key" user@$public_ip << \EOF
> i=1
> workerips="ip1 ip2"
> for ip in $workerips; do echo "ipis: ${ip} and i is ${i}"
> done
> EOF

answered Jul 3, 2019 at 22:51

William Pursell

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3 Comments

codebee Over a year ago

thanks, but I want to run it in an automated script and not an interactive session.

William Pursell Over a year ago

You can use heredocs just fine in a script. The fact that I've displayed an interactive session doesn't change anything. Just remove the first two columns of prompt.

codebee Over a year ago

Do you know why the 'for' loop is not working inside the heredoc: << \EOF i=1 for ip in $worker_ips; do echo "ip is ${ip} and i is ${i}" $ip >> ~/uniquefile $i >> ~/uniquefile i=$((i+1)) done EOF commands outside the for loop are working.

kit.sirota · Accepted Answer · 2019-07-03 23:06:13Z

1

Depending on what you are trying to do, parallel ssh program (pssh) could work for you.

https://linux.die.net/man/1/pssh

The idea is you can execute the same command across the nodes you define (either across the board or in batches). Basic workloads might be updating a config file across several nodes, more complex cases include things like snapshots across a Cassandra cluster to make sure you have these run at nearly the same time.

answered Jul 3, 2019 at 23:06

kit.sirota

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