matching variables to condition - bash

Question

i want to write a new script but i'm absolutely n00b in bash scripting
for example i want that script do kubectl get cs ( check cluster health ) and stdout of kubectl get cs is here:
administrator#rgv:~$ kubectl get cs
NAME STATUS MESSAGE ERROR
etcd-0 Healthy {"health": "true"}
scheduler Healthy ok
controller-manager Healthy ok
How I'm to parse the STATUS column?
If three nodes are the in cluster and the cluster is healthy I want to print just "cluster healthy.". If one node is down print "cluster is to die."

Answer 1

You could use a tool called awk.
kubectl get cs | awk 'NR>1 && $2=="Healthy"{count++}
END{if(count==3){print "All healthy"}
else{
print "Cluster(s) dead"
}
}'

Answer 2

Simplistic approach:
if kubectl get cs | tail -n +2 | grep -vq Healthy ; then
echo "It's dead, Jim"
else
echo "All is fine in the realm!"
fi
tail -n +2 skips the first line, and the grep looks for lines that don't contain the string Healthy. That is, even one line without it will trigger the warning.
This, of course ignores the columns completely, so it will fail if a dead member can contain that same string elsewhere in the line.

Answer 3

In your example the STATUS field has a Healthy status.
If you want to parse it as to find out which line contains the string you can use grep:
For your example it would be: kubectl get cs | tr -s ' ' | cut -f2 -d ' ' | grep Healthy which would show you all the lines containing a healthy string in the second column which is STATUS.
To check if cluster is down you can use: kubectl get cs | tr -s ' ' | cut -f2 -d ' ' | grep Down.
Note: tr -s ' ' squeezes the spaces and then you pipe-it to cut it with cut -f2 -d ' ' which will give you whole the column. There is space between the two single quotes ('') thank you for noticing #ilkkachu.
If you want to use it in a script you can do create a file using:
vim cluster_check.sh
#!/bin/bash
if kubectl get cs | tr -s ' ' | cut -f2 -d ' ' | grep -q 'Healthy';
then
echo 'cluster healthy!'
else
echo 'cluster is to die!'
fi
Then exit vim with ESC :wq
Change the execution flag for chmod +x cluster_check.sh.
Then you can execute it via: ./cluster_check.sh