Ash eval wierdness

[Paul Smith]

On Wed, 2011-05-25 at 17:20 +0200, Harald Becker wrote:
> In principle you are right, but it depends on the version of bash.
> There exist two strategies which lead to different results in those
> cases. Some shells run the last process in a pipe in the current shell
> others the first process. If the shell runs the first process of a
> pipe, all variable changes done by remaining processes of the pipe are
> lost. If the shell runs the last process of a pipe, variable changes
> in the last process are kept and others are lost.

Is it really the case that there are shells that run the first command
in a pipeline in the current shell?  I've never heard of this.

There are some shells that run the last command in a pipeline in the
current shell: ksh does this for example.  The last time I checked bash
does NOT do this, although maybe this was added in the latest versions?
I don't remember if zsh does this or not.

All other shells I'm aware of fork _all_ the commands in the pipeline.

Either method is acceptable from the standpoint of POSIX, so no shell
script that uses #!/bin/sh should ever depend on the "ksh behavior".

I agree it's a shame because it is so often useful to preserve variables
in the final command.  But, that's the way it is and it seems unlikely
to change.