tiny patch to prevent head from closing pipes

Jilles Tjoelker jilles at stack.nl
Sun Aug 29 21:00:45 UTC 2010

On Sat, Aug 28, 2010 at 06:42:29PM +0400, Anonymous wrote:
> Alexander Best <arundel at freebsd.org> writes:

> > i just had subversion complain about a broken pipe while piping its
> > output through awk straight to head [1]. i decided to add a switch
> > to head which will tell it to never close a pipe unless the input
> > has stopped [2].

> You can do same with sh(1), e.g.

>   $ svn log | (IFS=; while read li; do [ $((i+=1)) -le 10 ] && echo "$li"; done)

> versus

>   $ svn log | (IFS=; while read li && [ $((i+=1)) -le 10 ]; do echo "$li"; done)
>   ...
>   svn: Write error: Broken pipe

Even easier (and avoiding mangling through read) is
  svn log | { head; cat >/dev/null; }
Beware that the cat command will not necessarily get all of the input.
head may buffer reads and it is unable to push the extra data back onto
the pipe.

> But I think subversion should

I think Subversion should not print an error message for broken pipe on
its stdout.

> > there's probably a much more efficient way of discarding the input
> > without closing the pipe unless the input ceased. it's just a 5
> > minute hack in order to see if people find the idea useful or not.
> > ;)

> Can you give an example of usefulness that does not involve subversion?

Jilles Tjoelker

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