Adding a grid to my math lecture files

I really enjoy using xournal++ for my math course. It allows me to take handwritten notes and annotate my lecture files. While our teacher does a really good job at properly formatting those documents with LaTeX, it always has been hard for me to maintain a straight line on a plain sheet of paper. Unfortunately there is no feature of xournalpp I know of, which would allow me to overlay a grid on top of a pdf file. So I had to come up with something on my own:

grid=$(cat $HOME/docs/grid.svg)

rm -rf /tmp/pdfgrid
mkdir -p $_
mv "$1" $_
cd $_

pdf2svg "$1" %02d.svg all

for page in *.svg; do
	sed -i -e '/<\/svg>/d' $page
	echo "$grid" >> $page
	echo "</svg>" >> $page
done

rsvg-convert -f pdf -o out.pdf *.svg

cd -
mv /tmp/pdfgrid/out.pdf "$1"

I use pdf2svg to slice an entire pdf into an svg file per page. For every page, I append a grid which is just a path with strokes and an opacity. At the end, I use rsvg-convert to assemble the pdf from the svg files again and voilà, all the pages have a grid now!