How to execute mongo commands through shell

Lets say you need to find out which is the primary node in the mongo cluster in your shell script,

mongo –host 10.126.71.162 –username=userid –password=secret –eval “db.runCommand(‘ismaster’).primary”

This would quickly open the mongo shell and execute the commands, and give the output as the last line

MongoDB shell version v4.0.5
connecting to: mongodb://10.126.71.162:27017/?gssapiServiceName=mongodb
Implicit session: session { “id” : UUID(“65f2e5ab-aa97-4306-8a20-afd70a4ceeb0”) }
MongoDB server version: 4.0.5
10.126.71.162:27017