Can not extract the capture group with neither sed nor grep

Question

I want to extract the value pair from a key-value pair syntax but I can not.
Example I tried:

echo employee_id=1234 | sed \'s/employee_id=\\([0-9]+\\)/\\1/         


        

Answer 1

use sed -E for extended regex

    echo employee_id=1234 | sed -E 's/employee_id=([0-9]+)/\1/g'