phone number formatter

fmt-phone.sh

#!/bin/bash -

_format_phone_number()
{
    local one
    local phone="$(tr -d '[:punct:]' <<< $1)"

    if [[ $phone = *[!0-9]* ]] ||
       [ ${#phone} -lt 3 ] ||
       [ -z "$phone" ]
    then
      phone=""
    fi

    if [ "${phone:0:1}" = "1" ] &&
       [ ${#phone} -eq 11 ]
    then
       phone="${phone:1}"
       one="1-"
    fi

    case ${#phone} in
      6|7    )  phone="${phone:0:3}-${phone:3}" ;;
      8|9|10 )  phone="${phone:0:3}-${phone:3:3}-${phone:6}" ;;
    esac

    echo "${one}${phone}"
}

_format_phone_number "$@"