Leetcode: Valid Phone Numbers

Question

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

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Solution

Mistakes made

1. didn’t realize extended regular expression

Correct Solution

Solution 1 (sed)

sed -nr ‘/^([0-9]{3}-){2}[0-9]{4}$|^([0-9]{3}) [0-9]{3}-[0-9]{4}$/p’ file.txt

sed does not support \d in regular expression
It is necessary to use “sed -r (support extended regular expression)” so that we can use {n}.

Solution 2 (grep)

cat file.txt | grep -E ‘^([0-9]{3}-){2}[0-9]{4}$|^([0-9]{3}) [0-9]{3}-[0-9]{4}$’

grep should be used along with -E to support extended regular expression

Solution 3 (awk)

awk –posix ‘/^([0-9]{3}-){2}[0-9]{4}$|^\([0-9]{3}\) [0-9]{3}-[0-9]{4}$/{print $0}’ file.txt

–posix is added to support

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take-home message

When using regular expression, take care about whether it (awk, sed or grep) supports extended regular expression. It is safe to enable it once we want to use regular expresion

sed -r ‘/pattern/p’ filename
awk –posix ‘/pattern/{action}’ filename
cat filename | grep -E ‘pattern