sort -n info page

[Dan Jacobson]

We see
`--numeric-sort'
     Sort numerically: the number begins each line; specifically, it
     consists of optional blanks, an optional `-' sign, and zero or more
     digits possibly separated by thousands separators, optionally
     followed by a decimal-point character and zero or more digits.  A
     string of no digits is interpreted as `0'.  The `LC_NUMERIC'
     locale specifies the decimal-point character and thousands
     separator.

"no digits": say "non digits", and mention
"You'll be sorry if your lines don't start with a number, because
...", E.g.,
$ seq -f t%g 33|sort -un
t1

"If you want sort to peer into the line, only considering numbers
buried within, you'll have to do ..."

$ sort --version
sort (GNU coreutils) 5.97