    Read lines from the standard input into an indexed array variable.
    
    Read lines from the standard input into the indexed array variable ARRAY, or
    from file descriptor FD if the -u option is supplied.  The variable MAPFILE
    is the default ARRAY.
    
    Options:
      -n count	Copy at most COUNT lines.  If COUNT is 0, all lines are copied.
      -O origin	Begin assigning to ARRAY at index ORIGIN.  The default index is 0.
      -s count 	Discard the first COUNT lines read.
      -t		Remove a trailing newline from each line read.
      -u fd		Read lines from file descriptor FD instead of the standard input.
      -C callback	Evaluate CALLBACK each time QUANTUM lines are read.
      -c quantum	Specify the number of lines read between each call to CALLBACK.
    
    Arguments:
      ARRAY		Array variable name to use for file data.
    
    If -C is supplied without -c, the default quantum is 5000.  When
    CALLBACK is evaluated, it is supplied the index of the next array
    element to be assigned and the line to be assigned to that element
    as additional arguments.
    
    If not supplied with an explicit origin, mapfile will clear ARRAY before
    assigning to it.
    
    Exit Status:
    Returns success unless an invalid option is given or ARRAY is readonly or
    not an indexed array.
