A helper for converting CSV files into a LaTeX command format, so that the data can be used for mail merge letters.

LaTeX is a phantastic tool for composing and writing mail merges. The LaTeX document classes letter and scrlttr2 provide the implementation of typesetting letters of all kind.

For writing a mail merge, it has been a common way to wrap the letter class into a created command and then call this command multiple times. In composition with the ifthen-package, a minimal example looks like this:

\documentclass[paper=a4, fontsize=12pt]{scrlttr2}
% other packages
\usepackage{ifthen}
% ...
% set letter options
\begin{document}
% create command mallmerge with two arguments: (1) last name, (2) first name
\newcommand{mailmerge}[2]{
    \begin{letter}{#2 #1}
    \opening{Dear #2,}
    This is a minimal mail example of creating multiple personalized letters.
    \closing{With Kind Regards}
    \end{letter}
}
\end{document}
% input data.tex which contains the data
\input{data}

Note the last line of this minimal working example: We included an other TeX-file called data.tex which is supposed to call the created \mailmerge-command. An example content would be:

\mailmerge{Newton}{John}
\mailmerge{James}{Mary}
\mailmerge{Smith}{Anthony}

This would create three letters with the adapted content. But where does the data come from? Mostly we would use Excel/Calc-Sheets where we have tables of customers, friends, etc. which we would like to address. In this case, it would be very complicated to manually create an adapted LaTeX command for each entry. Here latexmailmerge steps in. It can convert a CSV file into a TeX file with the appropriate content which then can be used to create a mail merge.

A basic usage would look like that:

latexmailmerge -f1 -d "," --latex-command="\mailmerge" data.csv > data.tex

The argument -f specifies the first line (for skipping headlines) and is zero based. The argument -d specifies the delimater which is most likely "," or ";". data.csv is the source file and data.tex is the file where the output will be saved.

You can see a complete list of possible options via latexmailmerge --help.

The program is written in Rust. Clone the repository and compile the project using Cargo:

git clone https://github.com/reckel-jm/latexmailmerge.git
cargo build --release

If you manage a LaTeX project, it can become inconvinient to rerun the helper everytime when the CSV file has changed. You can let make do this for you. Create a Makefile with for example the following content:

letter.pdf: letter.tex data.tex
    latexmk -pdf letter.tex

data.tex: data.csv
	latexmailmerge -d ";" -f 1 -c "\mailmerge" data.csv > data.tex 

At compilation, Rust creates both an executable file which is the program as well as a dynamic library from the lib.rs file. This file has an exported function pub extern "C" fn convert_csv_file(c_str_filename: *const c_char, c_str_delim: *const c_char, c_uint_startline: c_uint, c_str_latex_command: *const c_char) -> *mut c_char which can be called from other programing languages. For example, in Python you could call the function via:

def convert2csv(filename, delim, firstline, latexcommand):
	import ctypes
	rust_lib = ctypes.CDLL("./liblatexmailmerge.so") # or any other file path depending on OS
	rust_lib.convert_csv_file.restype = ctypes.c_char_p
	return(rust_lib.convert_csv_file(filename.encode('utf-8'),
		delim.encode('utf-8'),
		ctypes.c_uint(firstline),
		latexcommand.encode('utf-8')).decode("utf-8"))