How to underline section-headings in LaTeX?

Question

EDIT: As I see in the first answer, underline is the wrong word. I want a line under the section heading, separating the heading from the following text.

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Answer 1

I've heard that the titlesec is more powerful than sectsty package, so I've just used it. You can put the horizontal line before the section header using:

\usepackage{titlesec}
\titleformat{\section}{\large\bfseries}{\thesection}{1em}{\hrule}

or you can put it after, with the help of newcommand. See section 4.4 of the titlesec manual.