Problem
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

Solution

# Read from the file file.txt and output all valid phone numbers to stdout.
egrep -e ^'\([0-9]{3}\) [0-9]{3}-[0-9]{4}'$ -e ^'[0-9]{3}-[0-9]{3}-[0-9]{4}'$ file.txt

Discussion

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

Using sed:

sed -n -r '/^([0-9]{3}-|\([0-9]{3}\) )[0-9]{3}-[0-9]{4}$/p' file.txt

Using awk:

awk '/^([0-9]{3}-|\([0-9]{3}\) )[0-9]{3}-[0-9]{4}$/' file.txt