How do I make a long underscore in Plain TeX?

Question

I have looked at this question as well as here and here but I cannot figure out how to produce a long underscore in plain TeX, as in the following example.

Date _____________________________

The closest I have come is the obviously undesirable concatenation which leaves gaps in the rendered output.

Date  \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Answer 1

Use a negative height and a slightly bigger depth:

\vrule height -3pt depth 3.4pt width 7cm

Adjust to suit.

The same idea can be used for “raised rules” (with a negative depth). No rule will appear if depth + height is negative.

If you want a “low rule” that fills up a given space, leaders should be used:

\def\lowhrulefill{%
  \leavevmode % be sure to be in horizontal mode
  \leaders\hrule height height -3pt depth 3.4pt\hfill % fill all available space
  \kern0pt % so \par won't remove the rule
}

Note that \leavevmode is necessary because the command appearing in vertical mode would raise an error because of \hfill (and would do nothing good either).

Answer 2

Plain TeX already defines an \hrulefill command that does this. Use it like this:

\noindent
Date \hbox to 3cm{\hrulefill}

\bye

to produce

If you would rather have the line drawn a bit lower down, then try this:

\noindent
Date \lower.2ex\hbox to 3cm{\hrulefill}

\bye

If you were going to use it more than a few times, then you could make a macro:

\def\filler#1{\noindent\lower.3ex\hbox to #1{\hrulefill}}

\noindent
Date \filler{3cm}

\bigskip
\noindent
Name: \filler{2in}

\bigskip
\filler{\hsize}

\bye