SELECT SUBSTR('abc_20130253_5667_[03-defg]_hgtyfd.edrf',5) AS A FROM dual;

SELECT SUBSTR('abc_20130253_5667_[03-defg]_hgtyfd.edrf', -3) AS A FROM dual;

SELECT INSTR('abc_20130253_5667_[03-defg]_hgtyfd.edrf','.', 1, 1) AS A FROM dual;

SELECT SUBSTR('abc_def.doc', INSTR('abc_def.doc','.', 1, 1)+1) AS A FROM dual;

SELECT REGEXP_REPLACE('abc_20130253_5667_[03-defg]_hgtyfd.edrf', '[^[:digit:]]') AS A FROM dual;

SELECT SUBSTR(REGEXP_REPLACE('abc_20130253_5667_[03-defg]_hgtyfd.edrf', '[^[:digit:]]'),1,6) AS A FROM dual;

SELECT REGEXP_SUBSTR('Orhan_Eripek#ora#cle.com','[^\#]+',1,LEVEL) AS A FROM dual
 CONNECT BY LEVEL <=  REGEXP_COUNT('Orhan_Eripek#ora#cle.com', '\#')+1;