cp -if a b: should it prompt? POSIX says `yes', most don't

[Jim Meyering <yyy@xxxxxxxxxxxx>]

There is a discrepancy between POSIX and common practice
with respect to how `cp -if a b' should work.

According to POSIX,
  http://www.opengroup.org/onlinepubs/007904975/utilities/cp.html
cp must prompt the user in this case (GNU cp and Solaris cp do this):

  $ touch a b; /bin/cp -if a b
  cp: overwrite b (yes/no)?

However, many[1] existing implementations of cp do not prompt
because they define -f to override any preceding -i option:

  $ touch a b; /bin/cp -if a b
  $

POSIX says that -i means `prompt' and that -f is unrelated.
POSIX requires cp's -f option to make it so that if an existing
destination file cannot be opened, cp removes it and tries again.

But bear in mind that for both rm and mv, the -f and -i options
*are* related.  For both of those tools, a -f option cancels the
effect of any preceding -i option.

Note that RedHat has been using a patch that makes cp's behavior
non-POSIX, yet consistent with that of most other systems, for years.

I'm inclined to change the `upstream' GNU cp to be non-conforming, too.

Should POSIX permit the existing behavior of cp on all of those
other non-Solaris systems?

Jim

-------------
[1] The following systems provide an implementation of cp that is not
POSIX compliant in that `cp -if a b' completes without prompting:
  Tru64 V5.1
  openbsd 3.2
  netbsd 1.6
  HPUX B.11.23
  Darwin 7.2.0
  RedHat

On the other side of the fence:

  solaris-5.9 /bin/cp
  solaris-5.9 /usr/xpg4/bin/cp
  cp from the GNU coreutils package