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.

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⌗ 

echo "clean file"
rm file.txt

echo "make file to test"
cat << EOF > file.txt
987-123-4567
123 456 7890
(123) 456-7890
EOF

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