Use like in PL/SQL : Like « PL SQL Operators « Oracle PL/SQL Tutorial

1. Oracle PL/SQL Tutorial
2. PL SQL Operators
3. Like

SQL> SET ECHO ON
SQL>
SQL> CREATE OR REPLACE FUNCTION area_code (phone_number IN VARCHAR2)
  2  RETURN VARCHAR2 AS
  3  BEGIN
  4    IF phone_number LIKE '___-___-____' THEN
  5      RETURN SUBSTR(phone_number,1,3);
  6    ELSE
  7      RETURN 'none';
  8    END IF;
  9  END;
 10  /

Function created.

SQL>
SQL>