分析

難度 易

來源

https://leetcode.com/problems/valid-phone-numbers/

題目

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

解答

https://leetcode.com/problems/valid-phone-numbers/discuss/55478/Grep-e-solution-with-detailed-explanation-good-for-those-new-to-regex

1 grep -e '\(^[0-9]\{3\}-[0-9]\{3\}-[0-9]\{4\}$\)' -e '\(^([0-9]\{3\})[ ]\{1\}[0-9]\{3\}-\([0-9]\{4\}\)$\)'  file.txt

1. In Bash, we use \ to escape next one trailing character;
2. ^ is used to denote the beginning of a line
3. $ is used to denote the end of a line
4. {M} is used to denote to match exactly M times of the previous occurence/regex
5. (...) is used to group pattern/regex together

Back to this problem: it requires us to match two patterns, for better readability, I used -e and separate the two patterns into two regexes, the first one matches this case: xxx-xxx-xxxx and the second one matches this case: (xxx) xxx-xxxx

加上-P（使用Perl的正則引擎）即可過濾出目標資料

1 grep -P '^(\d{3}-|\(\d{3}\) )\d{3}-\d{4}$' file.txt

注意上方的空格 

1 grep '^(\d{3}-|\(\d{3}\)[ ]{1})\d{3}-\d{4}$'  file.txt

這裡使用[ ]{1}表示一個空格