原文：
https://leetcode.com/problems/valid-phone-numbers/
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: -- () -
Your script should output the following valid phone numbers:
--
() -
简单点说，就是只要符合那两种的都是合格的号码，输出来就可以。
答案
cat file.txt |grep -E "(^\([0-9]{3}\) [0-9]{3}-[0-9]{4}$)|(^([0-9]{3}-){2}[0-9]{4}$)"
这其中使用了grep -E命令，其表示命令中使用正则。
正则有^(表示开头)和$(表示结尾)，[0-9]表示从0开始到9之间的数包括0和9，{n}表示匹配n次。
其中\(\)表示小括号转义。