paolobrasolin/antex

\documentclass{article}
\pagestyle{empty}

\newbox\snippet
\setbox\snippet=\hbox{\rule{1em}{1ex}}

\newdimen\oneem
\oneem=1em
\newdimen\oneex
\oneex=1ex

\newwrite\metrics
\immediate\openout\metrics=\jobname.yml
\immediate\write\metrics{ex: \the\oneex}
\immediate\write\metrics{em: \the\oneem}
\immediate\write\metrics{ht: \the\ht\snippet}
\immediate\write\metrics{dp: \the\dp\snippet}
\immediate\write\metrics{wd: \the\wd\snippet}
\immediate\closeout\metrics

\begin{document}\box\snippet\end{document}

%\newsavebox\snippet
%\newlength\height
%\newlength\depth
%\newlength\width
%
%\begin{lrbox}{\snippet}\rule{1ex}{1ex}\end{lrbox}
%
%\settoheight\height{\usebox\snippet}
%\settodepth \depth {\usebox\snippet}
%\settowidth \width {\usebox\snippet}
%\makeatletter
%\newwrite\file
%\immediate\openout\file=\jobname.yml
%\immediate\write\file{ex: \strip@pt\dimexpr 1ex}
%\immediate\write\file{dp: \strip@pt\depth}
%\immediate\write\file{ht: \strip@pt\height}
%\immediate\write\file{wd: \strip@pt\width}
%\addtolength{\height} {\depth}
%\immediate\write\file{th: \strip@pt\height}
%\closeout\file
%\makeatother