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.

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

cat > file.txt <<EOF
987-123-4567
(123) 456-7890
0(001) 345-0000
(001) 123-345
123 456 7890
EOF

匹配形如(xxx) xxx-xxxx or xxx-xxx-xxxx的模式


第一种,使用awk：
awk '/^(\([0-9]{3}\) |[0-9]{3}-)[0-9]{3}-[0-9]{4}$/' file.txt 
等同于
awk '/^(\([[:digit:]]{3}\) |[[:digit:]]{3}-)[[:digit:]]{3}-[[:digit:]]{4}$/' file.txt 

用awk命令+RE解决。 
开始及结尾处的 / 是正则表达式的定界符（在一些语言里要求使用）。 
^ 表示无其他前缀。 
$ 表示无其他后缀。 
| 表示两种匹配选一个。 
这里匹配中的 ( 需要转义。

第二种，用基本正则表达式：

grep "^\(([0-9]\{3\}) \|[0-9]\{3\}-\)[0-9]\{3\}-[0-9]\{4\}$" file.txt
等价于
grep "^\((\d\{3\}) \|\d\{3\}-\)\d\{3\}-\d\{4\}$" file.txt

第三种，用扩展的正则表达式：

grep -E "^(\([0-9]{3}\)\s|[0-9]{3}-)[0-9]{3}-[0-9]{4}$" file.txt
等价于
grep -E "^(\(\d{3}\)\s|\d{3}-)\d{3}-\d{4}$" file.txt