set-dpi.sh

#!/bin/bash
#==========
# Uses the GIMP to set the specified DPI value on the specified image without
# changing the dimensions of the image.
#
# This is useful as Inkscape provides no means of changing the DPI of an exported
# image without altering its pixel count, and also defaults to 90dpi.
#
# Note that gimp-console must be in your $PATH.

dpi=$1
img=$2
if [ "$dpi" -a "$img" ]; then
  echo "Setting DPI of \"$img\" to $dpi... ";
  gimp-console -i -b "
    (let* (
      (image (car (gimp-file-load RUN-NONINTERACTIVE \"$img\" \"$img\")))
      (drawable (car (gimp-image-get-active-layer image)))
    ) (
      (gimp-image-set-resolution image $dpi $dpi)
      (gimp-file-save RUN-NONINTERACTIVE image drawable \"$img\" \"$img\")
      (gimp-quit 0)
    ))
  "; 
else
  echo "Usage: $0 <dpi> <img>";
fi