Bug 2457

I was trying today to filter my access.log apache log with some coreutils
and was annoyed by the default buffering applied by glibc.
I was trying to do `tail -f ~/access.log | cut ... | uniq` but I was
only getting output when cut had more than 4K written to stdout.

So how to control this? Well each app could add an extra config
parameter (see grep --line-buffered for example), but this doesn't
seem general, and just requires duplicating both logic and documentation
for each application. What would be ideal IMHO would be to
add the config logic in glibc (which would have to be controlled
with environment variables). There seems to be resitance to that though:
http://sources.redhat.com/ml/bug-glibc/1999-09/msg00041.html

Anyway whether it's implemented in libc or the application (coreutils lib),
I think they should have the same config interface which would
be environment variables with something like the following format:
    BUF_X_=Y
Where X = the fd number
and Y = 0 for unbuffered, 1 for line buffered and >1 for a specific
buffer size.

So for my particular problem I could do:

tail -f ~/access.log | BUF_1_=1 cut ... | uniq