

          bsearch filehandle key [retvar] [compare_proc]
               Search an opened sorted data file, filehandle, for a
               line matching key. If retvar is specified, then the
               line from the file is returned in retvar and the
               command returns 1 if key was found, and 0 if it was not
               found.  If retvar is not specified or is a null name,
               then the command returns the line that was found, or an
               empty string if key is not found.

               By default, the key is matched against the first
               white-space seperated field in each line.  The field is
               treated as an ASCII string.  If compare_proc is
               specified, then it is the name of a Tcl procedure to
               evaluate against each line read from the file.  This
               compare_proc takes two arguments, the key and a line
               extracted from the file.  The compare routine should
               return a number less than zero if the key is less than
               the line, zero if the key matches the line or greater
               than zero if the key is greater than the line.  The
               file must be sorted in assending order by whatever
               criteria compare_proc uses to compare the key with the
               line.
