Re: Re[2]: [9fans] weird print(2) problems...

["Boyd Roberts" <boyd@fr.inter.net>]

> Re: zero length messages on pipes
>
> I understood that read would return 0 for a zero length message,
> and -1 on a read of a hungup (broken) pipe.

on unix a broken pipe is when the reader goes away.  the writer
then gets sigpiped/epipe on the next write.  the writer can exit
before the reader, with no ill effects.

err, if you were using a version of csh (all versions?) this could
bite you badly 'cos a pipeline was incorrectly constructed;  csh
would wait on the first process and not the _last_.  you have to
fork the pipeline in reverse to get the right semantics, but csh
did not do this.  sh did.

if your pipeline is:

    cmd | grep something > /dev/null

it's the exit status of the grep that you want, not the exit
status of cmd.

8th ed was modified to deal with dumb readers/writers by sigpipe,
then sigkill after some number of bogus i/o's -- this was to
trap programs that ignored error conditions.  i guess this was
initially added to limit the consumption of stream resources.

dennis will correct me.  it's early, i haven't even finished
my first coke.