How to trim substrings?

Help, please.

I have to query a table to trim a certain field, and to catch its certain substrings. The tool I know is like ltrim() or rtrim(), something like

select ltrim(ltrim(field_1,'a'),'b') from table_1;

or

select count(*) from table_1 where rtrim(field_1,'b') = 'xxc';

I know ltrim() or rtrim() only trim out one character/digit once. How can I get all of the required results if I have more repeated 'a' to the left or 'b' to the right? Like

aHaveOne
aaHaveTwo
abaabHaveMore

...

This must be done purely by SQL*Plus query. Thanks. Received on Thu Mar 16 2006 - 12:32:06 CST