You have some question of ubuntu system.
1. Write a regular expression to match a valid US phone number, assuming there are two acceptable formats: (315)1234567, (800)123-4567.
Test your regular expression using "grep".
2. Modify the regular expression you used in the previous question to only match XXX area codes (315 and 680)
3. Use find command with -regex option to find all files that their names start with a lowercase letter.