Valid Phone Numbers

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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:

987-123-4567123 456 7890(123) 456-7890

Your script should output the following valid phone numbers:

987-123-4567(123) 456-7890

匹配形如(xxx) xxx-xxxx or xxx-xxx-xxxx的模式

主要用grep（基本正则表达式和扩展的正则表达式）

第一种，用基本正则表达式

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

第二种，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

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