How to print contents of variables?

It is often useful to print out the values of variables in the log file or on the terminal. Three possible ways to print out the contents of \textheight variable are:

1. \showthe\textheight
2. \message{The text height is \the\textheight}
3. \typeout{The text height is \the\textheight}

These techniques use the TeX primitives \the (which provides the value of a variable), \showthe (print a variable to the terminal and the log, on a line of its own), and \message, which interpolates something into the log. The command \typeout is LaTeX’s general message output mechanism.

In each case, the variable’s value is printed as a number of points.

To typeset the value of \textheight, just \the\textheight is enough, but a more flexible alternative is to use the printlen package. Printlen allows you to choose the units in which you print a variable; this is useful, given that the most ordinary people don’t think in points (particularly Knuth’s points, of which there are 72.27 to the inch).

So, using printlen, we could say:

\newlength{\foo}
\setlength{\foo}{12pt}
\verb|\foo| is \printlength{\foo}

and get: \foo is 12pt while, if we say:

\newlength{\foo}
\setlength{\foo}{12pt}
\uselengthunit{mm}
\verb|foo| is \printlength{\foo}

we get: \foo is 4.21747mm

FAQ ID: Q-printvar
Tags: latex–macros