template replacement on gnuplot script

#!/bin/bash -eu
typeset -g tempfile
template() {
  local path=$1
  local datetime=$2
  tempfile=$(mktemp -p .)
  cat <<-EOT >${tempfile}
  set terminal png
  set pm3d map
  set output "%d%.png"
  splot "%p%" u 1:2:3 notitle
EOT
  sed -i -e "s;%d%;${datetime};" -e "s;%p%;${path};" ${tempfile}
}

for path in *.txt; do
  datetime=$(head -n 1 ${path} | sed 's/^[^(]*(\([^)]*\)).*$/\1/')
  template ${path} ${datetime}
  gnuplot ${tempfile}
  rm -f ${tempfile}
done