Script to add simple text-based watermark to PDF

watermark.sh

#!/bin/bash

if [[ $# -lt 3 ]] || [[ $# -gt 4 ]]; then
  cat > /dev/stderr <<EOD
usage: $(basename $0) <src> <dst> <text> [opacity]
  src: input file to be watermarked
  dst: output file with watermark applied
  text: watermark text
  opacity: transparency, 10-99 (light-dark)
EOD
  exit 1
fi

if [[ ! -f $1 ]]; then
  echo "source file does not exist: $1" > /dev/stderr
  exit 2
fi

if [[ -f $2 ]]; then
  echo "destination file already exists: $2" > /dev/stderr
  exit 3
fi

d=$(mktemp -d)
# pdflatex -output-directory
pushd "$d" > /dev/null

echo -n "generating tex files.. " > /dev/stderr
cat > mark.tex <<EOD
\\documentclass{article}
\\usepackage{xwatermark}
\\usepackage{xcolor}
\\usepackage{transparent}
\\usepackage{calc}
\\newcommand{\\mytext}{$(sed -e 's/ä/\\\"a/g' -e 's/ö/\\\"o/g' -e 's/ü/\\\"u/' <<< "$3")}
\\newlength\\h
\\newlength\\w
\\setlength{\\h}{\\heightof{\\mytext}}
\\setlength{\\w}{\\widthof{\\mytext}}
\\newwallpaper[%
    allpages,fontfamily=qpl,%
    color=black,%
    boxalign=center,angle=45,%
    wallpaper-xoffset=.3\\w,%
    wallpaper-yoffset=-.4\\w,%
    tilexsize=1\\w,tileysize=1\\h,
    tilexoffset=-.25\\w,tileyoffset=2\\h%
]{\\transparent{0.${4:-70}} \\mytext}
\\begin{document}
\\shipout\\null
\\end{document}
EOD
echo done > /dev/stderr

function cmd {
  echo -n "$1.. " > /dev/stderr
  shift
  "$@" >stdout 2> stderr
  ret=$?
  if [[ $ret -ne 0 ]]; then
    echo error > /dev/stderr
    cat stdout > /dev/stderr
    cat stderr > /dev/stderr
    echo "error while running: $@" > /dev/stderr
    exit 128
  else
    echo done > /dev/stderr
  fi
}

for i in 1 2; do
  cmd "rendering pass $i (of 2)" pdflatex -interaction nonstopmode mark.tex
done

popd > /dev/null
cmd "stamping file" pdftk "$1" stamp "$d/mark.pdf" output "$2"
cmd "cleaning up" rm -r "${d:?}/"