expand unix variable inside sed command [duplicate

Question

This question already has an answer here:

• Replace a string in shell script using a variable 9 answers
• sed substitution with bash variables 4 answers

I need to replace current value in configuration file with new value which is assigned to variable ,

like

file_name=abc.txt

needs to be replaced like

file_name=xyz.txt

where $file=xyz.txt

I tried

sed -i 's/file_name=.*/file_name=$file/g'  conf_file.conf

however the variable is not getting expanded, it comes like file_name=$file.

any pointers?

Answer 1

This should work,assuming that variable file has value:xyz.txt assigned to it:

sed "s/file_name=.*/file_name=${file}/g" file_name

Output:

file_name=xyz.txt