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

    Runtime: 8 ms, faster than 100.00% of Bash online submissions for Valid Phone Numbers.

    1. # Read from the file file.txt and output all valid phone numbers to stdout.
    2. grep -P '^(\d{3}-|\(\d{3}\) )\d{3}-\d{4}$' file.txt