most extreme grep challenge

% ls
abc abcd q
% grep --version
grep (GNU grep) 2.5.1
% ls | grep ______
abc
========================================
Fill in the blank and no flags fags.  I will judge all entries,
and decide upon the winrars.

oh hi

% touch abc abcd q
% ls
abc  abcd  q
% grep --version
grep (GNU grep) 2.5.1
% man grep
[...]
-w, --word-regexp
Select  only  those  lines containing matches that form whole words.  The test is that the matching substring must either be at the beginning of the line, or preceded by a non-word constituent character.  Similarly, it must be either at the end  of  the  line  or followed by a non-word constituent character.  Word-constituent characters are letters, digits, and the underscore.
[...]
% ls | grep -w abc
abc