linux - How can I use grep and regular expression to display names with just 3 characters

Question

I am new to grep and UNIX. I have a sample of data and want to display all the first names that only contain three characters e.g. Lee_example. but I having some difficulty doing that. I am currently using this code cat file.txt|grep -E "[A-Z][a-z]{2}" but it is displaying all the names that contain at least 3 characters and not only 3 characters

Sample data

name	number
Lee_example	1
Hector_exaple	2

Answer 1

You need to match the _ after the first name.

grep -E "[A-Z][a-z]{2}_"