How to check the presence of a parameter in the config and if it is not filled, then add it?

Question

linux

I have a config like this:

PARAM_1 = 'one'
PARAM_2 = 'two'
PARAM_3 = ''
PARAM_4 = 'four'
...
PARAM_X = 'x'

In the given example, it is necessary to check the PARAM_3 string for the presence of the text 'three' in it, and if the string is empty, as in the given example, then write this value there.

Answer 1

sed -i "s|^PARAM_3 = ''|PARAM_3 = 'three'|" /path/to/file