Re: [bug #17457] "grep -r foo . > somefile" goes into an infinite loop

[Paolo Bonzini]

> Actually, how about detecting this and diagnosing
> the problem rather than falling into the infloop?
>
> This currently evokes an infloop for me:
>
>      $ seq 1000000>  k
>      $ grep 111 k>>  k
>
> However, simply detecting when the output FD is also an input FD is
> not enough, since this variant does not get stuck:
>
>      $ seq 1000>  k
>      $ grep 111 k>>  k

Whether it gets stuck is mainly a function of the buffer size for the 
file.  Certainly whatever is added at the end of "k" matches, so it will 
be added over and over.

This is a problem for every Unix utility that reads files sequentially 
(e.g. sed or, from coreutils, cut, cat, fmt, tail, comm).

Paolo