from the
man pages
man sort
+POS1 [-POS2]
Specify a field within each line to use as a sort-
ing key. The field consists of the portion of the
line starting at POS1 and up to (but not including)
POS2 (or to the end of the line if POS2 is not
given). The fields and character positions are
numbered starting with 0.
-k POS1[,POS2]
An alternate syntax for specifying sorting keys.
The fields and character positions are numbered
starting with 1.
A position has the form f.c, where f is the number of the
field to use and c is the number of the first character
from the beginning of the field (for +pos) or from the end
of the previous field (for -pos). The .c part of a posi-
tion may be omitted in which case it is taken to be the
first character in the field. If the -b option has been
given, the .c part of a field specification is counted
from the first nonblank character of the field (for +pos)
or from the first nonblank character following the previ-
ous field (for -pos).
A +pos or -pos argument may also have any of the option
letters Mbdfinr appended to it, in which case the global
ordering options are not used for that particular field.
The -b option may be independently attached to either or
both of the +pos and -pos parts of a field specification,
and if it is inherited from the global options it will be
attached to both. If a -n or -M option is used, thus
implying a -b option, the -b option is taken to apply to
both the +pos and the -pos parts of a key specification.
Keys may span multiple fields.
