Re: the context of expansion for output redirection

[Chet Ramey]

Lewis Hyatt wrote:
> Hello-
> 
> I was somewhat surprised to see the following behavior (this is 3.1.17):
> 
> $ x=0; /bin/echo > /tmp/$((++x)); echo $x
> 0
> $ x=0; echo > /tmp/$((++x)); echo $x
> 1
> 
> I guess in the first case the expansion of $((++x)) is taking place after
> forking, whereas in the second case there is no forked process so the 
> expansion
> happens in the context of the current shell. I would have thought that both
> cases would output "1", though. Is this expected or documented anywhere? 
> Thanks
> very much.

The Bash philosophy has always been that redirections are carried out in
the same context as the command they are part of.  That means that a
command that causes a subshell to be created will have its redirections
performed in that subshell environment.  Similarly for builtin commands
in the current shell context.

Chet
-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU    chet@case.edu    http://cnswww.cns.cwru.edu/~chet/