There are lot of options in Regular Expressions. As Ramin said, please read the Oracle docs regarding Regular Expressions. To search for matching pattern, you could use regexp_like. Similar to normal string operations, we have REGEXP_INSTR, REGEXP_SUBSTR, REGEXP_COUNT in Regular Expressions. Try reading each of these. I can give you an example for REGEXP_LIKE for your scenario. Try exploring how this works.
ELSE 'NOT MATCHING'
END AS PATTERN_RESULTS
( SELECT 'ABC123DEF' STR1 FROM DUAL
SELECT '*/\' FROM DUAL);