 by a Tcl extension. The channel must have
been opened for input.
<P>
If <I>varName</I> is omitted the line is returned as the result of the
command.
If <I>varName</I> is specified then the line is placed in the variable by
that name and the return value is a count of the number of characters
returned.
<P>
If end of file occurs while scanning for an end of
line, the command returns whatever input is available up to the end of file.
If <I>channelId</I> is in non-blocking mode and there is not a full
line of 