Can i know about logic framed to get output using the Regexp?

Question

Hi ,
I am now only studing the working concept of Regexp. I had seen best solution from Mr. Blus. Can i know how it is working. I need that logic of wild cards functionality in Regexp Matching sting (wild card Matching string).
SQL> ed
Wrote file afiedt.buf
  1  WITH test_data AS (
  2  SELECT 'c:\temp\folderA\fileA.txt' t FROM DUAL UNION ALL
  3  SELECT 'c:\temp\fileA.txt' t FROM DUAL UNION ALL
  4  SELECT '\\mymachine\A\fileB.txt' t FROM DUAL UNION ALL
  5  SELECT '\\mymachine\A\B\fileB.txt' t FROM DUAL UNION ALL
  6  SELECT '\\mymachine\A\B\C\image.jpg' t FROM DUAL UNION ALL
  7  SELECT '\\mymachine\A\B\C\D\music.mpg' t FROM DUAL UNION ALL
  8  SELECT 'c:\myfolder\folderD\folderE\4969-A.txt' t FROM DUAL
  9  )
10  select regexp_replace(t, '^.*[\]([^\]*)[\][^\]*$','\1')
11* from test_data
SQL> /
REGEXP_REPLACE(T,'^.*[\]([^\]*)[\][^\]*$','\1')
folderA
temp
A
B
C
D
folderE
7 rows selected.
SQL>Please help me in this regards.
Kanish

Answer 1

Kanish wrote:
One more question what is the mean of
The final '\1' in
select regexp_replace(t, '^.*[\]([^\]*)[\][^\]*$','\1') kanishthis is a back reference.
see here:
http://download.oracle.com/docs/cd/B19306_01/appdev.102/b14251/adfns_regexp.htm#CHDHCIGH
and in the middle of the table here:
http://download.oracle.com/docs/cd/B19306_01/appdev.102/b14251/adfns_regexp.htm#CHDIEGEI
Matches the nth preceding subexpression, that is, whatever is grouped within parentheses, where n is an integer from 1 to 9. The parentheses cause >an expression to be remembered; a backreference refers to it. A backreference counts subexpressions from left to right, starting with the opening >parenthesis of each preceding subexpression. The expression is invalid if the source string contains fewer than n subexpressions preceding the \n.
Oracle supports the backreference expression in the regular expression pattern and the replacement string of the REGEXP_REPLACE function.
The expression (abc|def)xy\1 matches the strings abcxyabc and defxydef, but does not match abcxydef or abcxy.
A backreference enables you to search for a repeated string without knowing the actual string ahead of time. For example, the expression ^(.*)\1$ >matches a line consisting of two adjacent instances of the same string.
As explained in Table 4-2, back references store matched subexpressions in a temporary buffer, thereby enabling you to reposition characters. You access buffers with the \n notation, where \n is a number between 1 and 9. Each subexpression is contained in parentheses and is numbered from left to right.