On 3/25/20 3:02 PM, Richard Ipsum wrote:
On Wed, Mar 25, 2020 at 01:17:19PM -0500, Eric Blake wrote:
On 3/25/20 12:37 PM, Richard Ipsum wrote:
[snip]
See the difference? In the first case, sort is doing its default
case-insensitive comparison of the entire line (because you passed -f but
not -k), AND a stability comparison of the byte values of the entire line
(as shown by the two ____ lines per input). But in the second case, when
you add -s, the stability comparison is omitted. The two lines are indeed
different when the stability comparison is performed, explaining why -c
choked when -s is absent. Or put another way, -f affects only -k, including
the implied -k1 when you don't specify anything, and not -s. So now that we
know that, let's return to your example:
I'm trying to understand this relative to POSIX, which makes no mention
of stability as far as I can see (and there is no -s in POSIX). POSIX
says that -f should override the default ordering rules. I don't
understand why the last-resort comparison is required when -c is in use,
since we're not sorting with -c, just checking if the input is already sorted?
POSIX states [sort description]:
"If this collating sequence does not have a total ordering of all
characters (see XBD LC_COLLATE), any lines of input that collate equally
should be further compared byte-by-byte using the collating sequence for
the POSIX locale."
As I understand it, this is true even when -f modifies the collating
sequence to compare all lowercase characters as their uppercase equivalent.
But POSIX further states [XBD LC_COLLATE]:
"All implementation-provided locales (either preinstalled or provided as
locale definitions which can be installed later) should define a
collation sequence that has a total ordering of all characters unless
the locale name has an '@' modifier indicating that it has a special
collation sequence (for example, @icase could indicate that each upper
and lowercase character pair collates equally).
Notes:
A future version of this standard may require these locales to
define a collation sequence that has a total ordering of all characters
(by changing "should" to "shall").
Users installing their own locales should ensure that they
define a collation sequence with a total ordering of all characters
unless an '@' modifier in the locale name (such as @icase ) indicates
that it has a special collation sequence."
Put another way should -c imply -s ?
Maybe we compromise, and state that -c implies -s only for locales that
do not include @ in their name (that is, if a locale already guarantees
a total ordering of all characters, then even when -f collapses
lowercase into uppercase, we don't need the final-resort comparison; but
if a locale does not guarantee total ordering, the -s has to be explicit)?
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
