hyperref: How to open a directory view with href{...}?

The root of the problem is that hyperref tries to be smart. If no file extension is found, hyperref adds .pdf, so the link becomes either abc.pdf or abc/.pdf depending on whether there is trailing / in the call.

You can define your own command, say, \HREF, which simply constructs the link and does not do anything else.

This works for me:

\documentclass{article}
\usepackage{hyperref}
\makeatletter
\newcommand\HREF[2]{\hyper@linkurl{#2}{#1}}
\makeatother

\begin{document}
\HREF{tmp}{open directory \texttt{tmp}}
\end{document}

Note that this works in xpdf. Acrobat disables such links by security reasons. evince works with absolute paths (file:///home/boris/scratch) but balks at relative ones: somehow ../tmp/ works, but ./tmp does not. I guess this is some bug in evince.

As Boris said in his answer, .pdf is appended if no extension is found.

To avoid this, use \href{abc/.}{Open directory}. The . (current directory) looks like a file extension.