pdf-cover v.1.2

#!/bin/bash

###########################################
# NAME:     pdf-cover
# AUTHOR:   RelUnrelated, Copyright 2020
# LICENSE:  Creative Commons Attribution - Share Alike 3.0 http://creativecommons.org/licenses/by-sa/3.0/
#       You are free to use and/or modify this script. If you choose to distribute this script, with or
#       without changes, you must attribute credit to the author listed above.
# REQUIRES: ImageMagick, coreutils, GhostScript
# VERSION:  1.2 [2021-01-10]
# DESCRIPTION:  A script to add a cover created from an existing cover image to an existing PDF file.
###########################################

if [ $# -eq 0 ]
then
    echo "Please state cover image and the PDF file you want to add the cover to."
    exit 0
else

    image_filename=$1
    pdf_filename=$2
    pointsperinch="0.013888888888889"
    # Query files for information
    pagesize=`pdfinfo "$pdf_filename" | grep "Page size"`
    imagesize=`identify -verbose "$image_filename" | grep "Geometry:"`
    echo "Computing page dimensions"
    # Parse PDF "Page Size" into width and height in inches
    pagesize=${pagesize#Page size: }
    pagesize=${pagesize%% pts*}
    pagepts_x=${pagesize%% x *}
    pagepts_y=${pagesize#* x }
    pagein_x=`bc -l <<< "$pagepts_x * $pointsperinch"`
    pagein_y=`bc -l <<< "$pagepts_y * $pointsperinch"`
    # Parse image size and density
    imagesize=${imagesize#  Geometry: }
    imagesize=${imagesize%%\+*\+*}
    imagepx_x=${imagesize%%x*}
    imagepx_y=${imagesize#*x}
    # Calculate desired image density
    newdensity_x=`bc -l <<< "$imagepx_x / $pagein_x"`
    newdensity_y=`bc -l <<< "$imagepx_y / $pagein_y"`

    echo "PDF width:" $pagein_x "in"
    echo "PDF height:" $pagein_y "in"
    echo "Image Size:" $imagepx_x "pixels X by" $imagepx_y "pixels Y"
    echo "Desired Image Density:" $newdensity_x "ppi X by" $newdensity_y "ppi Y"

    # Convert the image print size using the new density
    echo "Rewriting image print size"
    convert "$image_filename" -density "$newdensity_x"x"$newdensity_y" -units PixelsPerInch "$image_filename"
    # Convert the new cover image to a PDF
    echo "Converting cover image to PDF"
    convert "$image_filename" cover.pdf
    # Combine the cover PDF file with the orignal PDF into a new file
    echo "Combining cover PDF with original PDF into file covered.pdf"
    gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -dAutoRotatePages=/None -sOutputFile=covered.pdf  cover.pdf "$pdf_filename"
    rm cover.pdf

fi

exit 0