In this recipe, we will see how to use the back-referencing operator in order to validate telephone numbers. Suppose telephone numbers in a certain city follow the rule: a number must be of exactly eight digits, and the first and second digit must be the same.
For example, the valid numbers of the city may be 44005600, 88008700, and so on. If the number entered starts with a zero or has length less than eight, an error should be displayed. We will see how a short validation program may be written.
For creating the program that checks the validity of a telephone number according to the given criteria, proceed as follows:
Declare a parameter having the name
tel_nowith eight characters.We then use the
find regexstatement to search for the pattern([1-9])\1[0-9]{6}in the telephone number entered by the user.The
ifstatement is then used for checking the return code. Forsy-subrc, having the value0, the messageNumber is Validis displayed...