193. Valid Phone Numbers

https://leetcode.com/problems/valid-phone-numbers/description/
^   start with
$   end with

basic regex
(   {   |    are regular characters matching ( { |
\(  \{  \| ...  are special operations
grep '^\([0-9]\{3\}-\|([0-9]\{3\}) \)[0-9]\{3\}-[0-9]\{4\}$' file.txt

extended regex
(   {   |    are special operations
\(  \{  \| ...  are escape characters matching ( { |
grep -E '^([0-9]{3}-|\([0-9]{3}\) )[0-9]{3}-[0-9]{4}$' file.txt