regex - Regular expression for certain amount of characters -

I am trying to change many URLs with TextWrangler, which is m.htm m should be lost, but only the total number of characters in the file name is 7. People with fewer characters should not be changed.

I have tried

  /.*? {7} m.htm /   
 but it does not work ...  
 What is the solution?  
 
 
 change  
  href = "([^"] *) Meaning:  href = " after any non   " character until a  /  (better than the latest: greedy) then 6 characters after a  m , then any "  The character is not  
 
  href = "1 \ / \ 2.htm \ 3"   
 mean:    \ 1 = [^ "] * \ 2 = {6} \ 3 = [^ "] *   
 Example  
  & lt; a href =" google.com/foo/bar/urzadjm.  If the files can be  htm  and  php , then I recommend to replace  .htm  with  (.htm | .php) )  (Warning to change the context behind the numbers!)