grep bug

[Robin Schoonover]

On Fri, 13 Feb 2004 19:51:23 -0700, Steve Young wrote:
>
> Arguably grep shouldn't eat up all your 
> memory when this happens but that's more of a GNU issue than a FreeBSD 
> issue, and really it would be kind of hard to handle 
> gracefully/portably.  Have you reported this to the gnu bugs mailing 
> address? It may conceivably use 100% CPU but it shouldn't try and grab 
> 100% memory too.
> 

grep has to pull in the entire line, and /dev/zero is a line with no
end, so it tries pulling it all into memory until there is no more memory
for a line to go into.  (This part has been mentioned on this list before.)

The reason is simple: regular expressions.  You may have a regex that
matches from beginning to end (^ to $), which means we need the entire line
before we can determine if there is a match or not.  plain grep (as far as
I know) shouldn't require an entire line to operate on, just the length of
the search.  (There may be other reasons too)

However, you rarely have lines long enough to make enough of a difference
to cause problems.  (1000 char lines? 1000000 char lines?)  IMHO, it
wouldn't be worth making the grep code more complex to handle such rare
cases.  

-- 
Robin Schoonover (aka End)
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