how to sed replace whole line with the string as variable?

Question

how to sed replace whole line with the string as variable ?

#!/bin/bash
ssh $1 ssh-keyscan -t rsa $1 > /tmp/$1
RSA=$(cat /tmp/$1)
echo $RSA
sed -i 's:'^"$1".*':'"$RSA"':' /etc/ssh/ssh_known_hosts
cat /etc/ssh/ssh_known_hosts | grep $1

It is storing the variable in RSA but not replacing, not sure what's wrong with sed part.

Answer 1

You can use the following command.

#!/bin/bash
ssh $1 ssh-keyscan -t rsa $1 > /tmp/$1
RSA=$(cat /tmp/$1)
echo $RSA
sed -i -e "/$1/ d" -e "/^$1/ a $RSA" /etc/ssh/ssh_known_hosts
cat /etc/ssh/ssh_known_hosts | grep $1

I modified as per your requirement to add if not line exists and replace if it exists.