Shell - sed not replacing variables


Im using this sed command in order to replace a line in the hosts file but as I run the script it looks like its not replacing the variables per their value...

sed -i 's/${host_db}/${new_db}   db-01/' /etc/hosts

Running using sh -x I get this:
+ new_db=
+ host_db='   db-01'
+ sed -i 's/${host_db}/${new_db}   db-01/' /etc/hosts

Anything I might be missing?

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sed -i 's/'${host_db}'/'${new_db}'   db-01/' /etc/hosts

sed -i "s/${host_db}/${new_db}   db-01/" /etc/hosts


The shell does not resolve variables enclosed by single quotes, so you must either take them out of the quotes (first solution) or use double quotes instead (second solution) - if there is nothing which shall be protected from the shell intentionally, that is.

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Shell Scripting

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