finding last match in a file

[Dag]

In article <87r8fplvq4.fsf at smtp.blueyonder.co.uk>, Keith O'Connell wrote:
> Dag <dag at animagicnet.no> writes:
> 
>> I have a number of very large files where I have to find the last line
>> which matches a certain experssion.  Currently I'm simply opening the
>> file and looping through it noteing each time a line matches and at the
>> end of the loop I see which was the last match.  However this is very
>> slow and inefficient.  Is there some way to read through the file
>> backwards and simply find first match starting from the end of the file.
>> The files are really too big to read the entire thing into memory.
> 
> 
> Would you not be able to use grep with the "-n" option. It will list
> all your matches with the lines numbered so you can see the last match
> having the highest line number. If you then use wc on the file you will
> get the total number of lines. Take one from the other and you can see
> how far from the end your last match is.
> 
> That seems to easy - Have I misunderstood you question?

The problem is that greping through large files with a fairly complex
regexp is taking far too long, esp. when I know that the last occurance is
almost always within the last 100 lines.

Dag