+POS1 [-POS2]
Specify a field within each line to use as a sortÂ
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.
From the FreeBSD 2.1 man page [1]
[1] https://www.freebsd.org/cgi/man.cgi?query=sort&apropos=0&sek...