shell to split a skycube generated in Blender to 6 files to use in skycube game environments

gistfile1.sh

#!/bin/bash
#########################################################################
# crop_sky.sh                                                           #
#########################################################################
#                        This file is part of:                          #
#                         WILD WITCH PROJECT                            #
#                     http://www.wildwitchproject/                      #
#########################################################################
#                             CC-BY-SA                                  #
#   Wild Witch Project by Marcos Augusto Bitetti is licensed under a    #
#   Creative Commons Attribution-ShareAlike 4.0 International License.  #
#   Based on a work at http://www.wildwitchproject.com/.                #
#   Permissions beyond the scope of this license may be available at    #
#   http://www.wildwitchproject.com/p/direitos-da-obra.html.            #
#########################################################################

if [ ! $1 ]
then
        echo Usage:
        echo ./crop_sky.sh input_image_file
        echo
        echo Select a skybox cube generated in Blender \(3x2 images\) and put the six generated images into your project.
        echo Ex.:
        echo ./crop_sky.sh mycube.png
        echo
        echo Dependencies: imagemagick
        echo     sudo apt-get install imagemagick
        exit 0
fi

WIDTH=$(convert $1 -print "%w" /dev/null )
HEIGHT=$(convert $1 -print "%h" /dev/null )
SIZE=$(expr $HEIGHT / 2)

COMMAND="convert $1 -crop "
COMMAND+=$SIZE
COMMAND+=x
COMMAND+=$SIZE

eval "$COMMAND+0+0 +repage -define png:color-type=2 left.png"
eval "$COMMAND+$SIZE+0 +repage -define png:color-type=2 front.png"
eval "$COMMAND+$HEIGHT+0 +repage -define png:color-type=2 right.png"
eval "$COMMAND+0+$SIZE +repage -define png:color-type=2 bottom.png"
eval "$COMMAND+$SIZE+$SIZE +repage -define png:color-type=2 top.png"
eval "$COMMAND+$HEIGHT+$SIZE +repage -define png:color-type=2 back.png"