Rotate an animated gif by a chosen amount, while maintaining the animation

gif_rotate.sh

#!/bin/bash

# Rotate an animated gif by a chosen amount, while maintaining the animation

if [ "$1" == "-h" ]; then
    echo "Usage: `basename $0` [rotation in degrees] [input file] [output file]"
    exit 0
fi

ROTATION=$1
INPUT=$2
OUTPUT=$3

TMP_DIR=$(mktemp -d)

# Arg checks
if ! [[ "$ROTATION" =~ ^[0-9]+$ ]]
then
    echo "Sorry integers only for rotation"
fi

# Split original gif
convert $INPUT -scene 1 +adjoin "$TMP_DIR/tmp_%02d.gif"

# Rotate frames
mogrify -rotate $ROTATION -alpha set -background none "$TMP_DIR/tmp_*.gif"

# Combine frames
convert "$TMP_DIR/tmp_*.gif" -loop 0 $OUTPUT