Manga converter for Kindle screen

manga.sh

#!/bin/bash

if [ ! -x $(which gm) ]
then
    echo "GraphicsMagick is required."
    exit 1
fi

TMPDIR=$(mktemp -d)

for file in *
do
    resolution=($(gm identify -format "%w %h" "$file" 2>/dev/null))
    if [ $? -eq 0 ] # Make sure if it's a valid image.
    then
        cp "$file" $TMPDIR/

        gm convert -rotate "-90>" "$TMPDIR/$file" "$TMPDIR/$file"

        gm mogrify -depth 4 -colorspace gray -type palette -geometry x800 "$TMPDIR/$file"
    fi
done

zip $(basename $(pwd)).cbz $TMPDIR/* > /dev/null
 
rm -r $TMPDIR