Re: move-if-change and parallel make

[Paul Eggert]

On 01/22/2011 08:03 AM, Ralf Wildenhues wrote:

> -if test -r "$2" && cmp -s -- "$1" "$2"; then
> +if test -r "$2" && $cmpprog -- "$1" "$2" >/dev/null; then
>    rm -f -- "$1"
>  else
> -  mv -f -- "$1" "$2"
> +  if mv -f -- "$1" "$2"; then :; else
> +    # Ignore failure due to a concurrent move-if-change.
> +    $cmpprog "$1" "$2" >/dev/null 2>&1 && rm -f -- "$1"

The two cmpprog invocations should be identical, but they're
not.  Only one has "--", and only one redirects stderr.

The 1st cmppprog invocation is protected by a test -r,
but the second one is not.  That doesn't sound right either.
Either both should be protected, or neither.  For what
it's worth, install-sh doesn't have the test -r.