Given a text file file.txt that contains list of phone numbers (one per line), write a one liner bash script to print all valid phone numbers.

You may assume that a valid phone number must appear in one of the following two formats: (xxx) xxx-xxxx or xxx-xxx-xxxx. (x means a digit)

You may also assume each line in the text file must not contain leading or trailing white spaces.

For example, assume that file.txt has the following content:

987-123-4567
123 456 7890
(123) 456-7890

Your script should output the following valid phone numbers:

987-123-4567
(123) 456-7890

直接grep实现，使用-P选项，使用perl正则表达式。

#!/bin/bash
grep -P '(^(\d{3}-){2}\d{4}$)|(^\(\d{3}\) \d{3}-\d{4}$)' file.txt