Is it possible to call a latex macro at the command line in order to return a string, not create a document?

Question

I'm curious as to whether there is a way to pass a small amount of LaTeX code to a compiler at the command line and return the string corresponding to the value of a variable or length.

For instance I would like to pass this code

\usepackage{calc}
\def\contnt{\tt{I wish I knew how much space was occupied by this string when typeset...}
\settowidth{\contntwdth}{\contnt}

and I'd like to indicate that the string output I'm after is the width of the content e.g.

\the\contntwdth

Any suggestions are greatly appreciated.

Answer 1

The texdef tool written by me can be used to display the definition of macros and the value of dimension and other registers. It also allows to add arbitrary other code before (-b) and after the definition/value is printed.

Your example would be (code got refactored):

$ texdef -t latex  -p calc -b '\newdimen\mydim \settowidth{\mydim}{\texttt{I wish I knew how much space was occupied by this string when typeset...}}' -v mydim

\the\mydim:
377.9967pt

If required a wrapper script could be written which inserts the actual text in the position and removes unwanted lines in the output.

Answer 2

Here's a simple Bash script, say getdim

#!/bin/bash
latex << EOF | sed -n -e '/^\*\*\*\*/s///p'
\documentclass{article}
\nofiles
\begin{document}
\settowidth{\dimen0}{\ttfamily $1}\typeout{***\the\dimen0}
\stop
EOF

If you run

bash getdim "test of script"

you get the following output

73.49936pt

(Thanks to Marc van Dongen for suggesting an improvement in the usage of sed.)

Answer 3

You can use \immediate\write18 to output the length. The MWE below yields:

The content width is 377.9967pt.

The same code can be used to evaluate lengths of different strings. Saving the code below as GetLength.tex, and running it from the command line as:

pdflatex -shell-escape "\def\contnt{\tt{Here is a different string}}\input{GetLength.tex}"  | grep "content width"

yields:

The content width is 136.49881pt.

Code:

\ifdefined\contnt
\else
    \def\contnt{\texttt{I wish I knew how much space was occupied by this string when typeset...}}
\fi

\documentclass{article}

\newlength{\contntwdth}
\settowidth{\contntwdth}{\contnt}
\begin{document}
    \immediate\write18{echo ""; echo "The content width is \the\contntwdth."}
\end{document}

Answer 4

Yes you can pass commands on the commandline without using any auxiliary files.

For example the following just outputs 377.9967pt The | sed -e "1,/loaded/d" at the end just deletes the startup banner and list of hyphenation patterns, if you don't have sed then just omit that bit.

$ pdflatex '\batchmode\newlength\contntwdth\def\contnt{\texttt{I wish I knew how much space was occupied by this string when typeset...}}\settowidth{\contntwdth}{\contnt}\scrollmode\typeout{\the\contntwdth}\batchmode\stop' | sed -e "1,/loaded/d"

377.9967pt

Note I changed \tt to \texttt as \tt is not defined in the LaTeX format, if you use the string as given in the question the output is

! Undefined control sequence.
\contnt ->\tt 

(In classes where \tt is defined the usage is not as used in the MWE, the syntax is {\tt text} not \tt{text} but in the base LaTeX format it is not defined at all.)

Answer 5

it is not clear to me what do you really want. However, here is a solution mit a savebox:

\documentclass{article}
\newsavebox\TBox
\newlength\TLength
\def\contnt#1{\savebox\TBox{#1}\setlength\TLength{\wd\TBox}}

\begin{document}

\contnt{\ttfamily I wish I knew how much space was occupied by this string when typeset \ldots}
The contents has a width of \the\TLength

\end{document}