find a pattern not followed by another pattern

[realtest]

Hi,

I have a big file (over a thousand records) e.g.:

store id: A
Processing...
store id: B
Processing...
store id: C
store id: D
Processing...
store id: E
Processing...
....

And for instance in the above example "store id: C" was not followed by the "Processing..." pattern, so I konw "store id: C" was not processed. Is there a one liner that I can use (preferably grep since I am most familiar with) to extract "store id: C" (or stores that are not followed by the "Processing..." pattern?

Any thoughts would be highly appreciated.

Thanks

cheers...

[Cabhan]

Not with grep. grep only supports POSIX regular expressions and extended regular expressions.

What you are looking for is called a negative lookahead assertion. It is basically a zero-length match that asserts that something does not exist. For instance (using Perl syntax):

/A(?!B)/

This matches any instance of 'A' that is NOT immediately followed by 'B'. It does not match the character following 'A' (hence this is a zero-length match).

Perl and Ruby both support these, as do Vim regular expressions. I'm sure that they are supported elsewhere as well.