the GNU version of look(1) does this:<p><pre><code>  NAME
     look — display lines beginning with a given string

     -b      Use a binary search on the given word list. If you are ignoring case with -f or ignoring non-alphanumeric characters with -d, the file must
             be sorted in the same way. Please note that these options are the default if no filename is given. See sort(1) for more information on
             sorting files.</code></pre>