Subject: Re: bug#26422: historical feature or grand daddy bug?

From: Paul Eggert <[email-masked]>
Date: Sun, 9 Apr 2017 12:04:34 -0700

Historically, 'sort' ignored the \n at the end of each line, so that 
empty lines (i.e., lines consisting only of a single \n) collated before 
all other lines. An earlier version of the POSIX spec was (mis)written 
to require treating the \n as part of the data, and during development 
in 1999 GNU sort was briefly changed to conform to that, but this was an 
error in the POSIX spec that was eventually fixed and GNU sort was 
changed back to the traditional behavior, before any release was made 
with the funky behavior.

So, it's not a bug that \t\n collates after \n, since "\t" is 
lexicographically after "".

As I understand it, the empty string should collate before all other 
strings in all POSIX locales, so empty lines should always sort first in 
'sort' output. I'm by no means a collation expert, though, and if I'm 
wrong I'd like to see a counterexample.

Come to think of it, 'sort' might be able to improve performance in the 
common case of sorting text files containing many empty lines, by merely 
counting the lines rather than storing them internally. I suppose this 
is a different topic, though.