[oops] Document what the ".0" in e.g., "-k 2,3.0" means, and...

* coreutils.texi (sort invocation): ... that it can be applied to the
field-end spec, but not the field-start one.  Patch from Evan Hunt.

Signed-off-by: Jim Meyering <jim@meyering.net>

1 files changed, 25 insertions, 21 deletions

diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index ab95db48a..ae072d74d 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -3584,9 +3584,21 @@ Other options are:
 @cindex sort field
 Specify a sort field that consists of the part of the line between
 @var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
-omitted), @emph{inclusive}.  Fields and character positions are numbered
-starting with 1.  So to sort on the second field, you'd use
-@option{--key=2,2} (@option{-k 2,2}).  See below for more examples.
+omitted), @emph{inclusive}.
+
+Each @var{pos} has the form @samp{@var{f}[.@var{c}][@var{opts}]},
+where @var{f} is the number of the field to use, and @var{c} is the number
+of the first character from the beginning of the field.  Fields and character
+positions are numbered starting with 1; a character position of zero in
+@var{pos2} indicates the field's last character.  If @samp{.@var{c}} is
+omitted from @var{pos1}, it defaults to 1 (the beginning of the field);
+if omitted from @var{pos2}, it defaults to 0 (the end of the field).
+@var{opts} are ordering options, allowing individual keys to be sorted
+according to different rules; see below for details.  Keys can span
+multiple fields.
+
+Example:  To sort on the second field, use @option{--key=2,2}
+(@option{-k 2,2}).  See below for more examples.
 
 @item -o @var{output-file}
 @itemx --output=@var{output-file}
@@ -3725,29 +3737,21 @@ consistency, @option{-M} has been changed in the same way.  This may
 affect the meaning of character positions in field specifications in
 obscure cases.  The only fix is to add an explicit @option{-b}.
 
-A position in a sort field specified with the @option{-k}
-option has the form @samp{@var{f}.@var{c}}, where @var{f} is the number
-of the field to use and @var{c} is the number of the first character
-from the beginning of the field.  In a start position, an omitted
-@samp{.@var{c}} stands for the field's first character.  In an end
-position, an omitted or zero @samp{.@var{c}} stands for the field's
-last character.  If the start field falls after the end of the line
-or after the end field, the field is empty.  If the
-@option{-b} option was specified, the @samp{.@var{c}} part of a field
-specification is counted from the first nonblank character of the field.
-
-A sort key position may also have any of the option letters @samp{Mbdfinr}
-appended to it, in which case the global ordering options are not used
-for that particular field.  The @option{-b} option may be independently
-attached to either or both of the start and
-end positions of a field specification, and if it is inherited
-from the global options it will be attached to both.
+A position in a sort field specified with @option{-k} may have any
+of the option letters @samp{Mbdfinr} appended to it, in which case the
+global ordering options are not used for that particular field.  The
+@option{-b} option may be independently attached to either or both of
+the start and end positions of a field specification, and if it is
+inherited from the global options it will be attached to both.
 If input lines can contain leading or adjacent blanks and @option{-t}
 is not used, then @option{-k} is typically combined with @option{-b},
 @option{-g}, @option{-M}, or @option{-n}; otherwise the varying
 numbers of leading blanks in fields can cause confusing results.
 
-Keys can span multiple fields.
+If the start position in a sort field specifier falls after the end of
+the line or after the end field, the field is empty.  If the @option{-b}
+option was specified, the @samp{.@var{c}} part of a field specification
+is counted from the first nonblank character of the field.
 
 @vindex _POSIX2_VERSION
 @vindex POSIXLY_CORRECT