Valid Phone Numbers Problem

Problem

Given a text file file.txt that contains a 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.

Examples

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

Method 1 - Using Regex

Code

grep "^\(([0-9]\{3\}) \|[0-9]\{3\}-\)[0-9]\{3\}-[0-9]\{4\}$" file.txt # Basic
grep -E "^(\([0-9]{3}\) |^[0-9]{3}-)[0-9]{3}-[0-9]{4}$"      file.txt # Extended Grep using -E
grep -P "^(\(\d{3}\) |\d{3}-)\d{3}-\d{4}$"                   file.txt # Perl flavoured Grep using -P

Lets look at perl flavoured grep command, as it is easier to read and understand: What in these parentheses should come in the beginning.

grep -P ‘^(\d{3}-

\d{3} - means 3 digits should come in these parenthesis.

grep -P ‘^(\d{3}-|\(\d{3}\) )’

| = Means Or

\(\d{3}\) )’ = \d{3}\ means it should contain 3 digit and a space

grep -P ‘^(\d{3}-|\(\d{3}\) )\d{3}-\d{4}’

\d{3}-\d{4} means 3 digits and 4 digits