sed - Replace Line which contains the Pattern match with a new line

Shell Programming and Scripting
1

I need to replace the line containing "STAGE_DB" with the line
"STAGE_DB $DB # database that contains the table being loaded ($workingDB)"

Here $DB is passed during the runtime.

How can I do this?

Thanks,
Kousikan

2 
sed "s/STAGE_DB/STAGE_DB    $DB    # database that contains the table being loaded ($workingDB)/" FILE > tempfile
3

sed 's/find_string/replace_string/g' file_name

it is used to repalce all strings