       1mbsearch 4m22mfileId24m 4mkey24m ?4mretvar24m? ?4mcompare_proc24m?
              Search  an  opened  file  4mfileId24m containing lines of text sorted
              into ascending order for a match.  4mKey24m contains  the  string  to
              match.   If  4mretvar24m is specified, then the line from the file is
              returned in 4mretvar24m, and the command returns 1m1 22mif 4mkey24m was  found,
              and  1m0  22mif  it  wasn't.  If 4mretvar24m is not specified or is a null
              name, then the command returns the line that was  found,  or  an
              empty string if 4mkey24m wasn't found.

              By  default,  the  key  is matched against the first white-space
              separated field in each line.  The field is treated as an  ASCII
              string.   If 4mcompare_proc24m is specified, then it defines the name
              of a Tcl procedure to evaluate against each line read  from  the
              sorted  file  during the execution of the 1mbsearch 22mcommand.  4mCom-0m
              4mpare_proc24m 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 ascending order  according  to
              the  same criteria 4mcompare_proc24m uses to compare the key with the
              line, or erroneous results will occur.

              This command does not  work  on  files  containing  binary  data
              (bytes of zero).
