ubuntu oneiric ocelot write desktop background image file

here is a script which takes in path to one or more directories containing images and writes a gnome desktop background file to show those images

#!/bin/bash

usage()
{
cat << EOF
usage: $0 -t transition_time -s static_time (-d dirs|-r recursive_dirs)

OPTIONS:
 -h      Show this message
 -t      required. time of transition between images, in seconds
 -s      required. time each image is show
 -d      comma separated list of directories containing images.
 -r      comma separated list of directories that contain images and
         other directories with more images

Either dirs, recursive_dirs, or both is required
EOF
if [[ -z $1 ]]; then exit 1; else exit $1; fi
}

set_img_paths()
{
 dir_path=$1
 find_opts=$2
 
 for file_path in $(find ${dir_path} ${find_opts} -type f)
 do
  mime_type=$(file --mime-type ${file_path})
  if [[ $mime_type =~ ^.*:[[:space:]]+image/(.*)$ ]]
  then
   img_paths[${#img_paths[*]}]=$file_path
  fi
 done
}

while getopts ":hd:r:t:s:" x
do
 case $x in
  h) usage 0 ;;
  t) transition_time=$OPTARG ;;
  s) static_time=$OPTARG ;;
  d) dirs[${#dirs[*]}]=$OPTARG ;;
  r) recursive_dirs[${#recursive_dirs[*]}]=$OPTARG ;;
 esac
done

if [[ -z $transition_time ]]; then usage; fi
if [[ -z $static_time ]]; then usage; fi
if [[ ${#dirs[*]} -eq 0 && ${#recursive_dirs[*]} -eq 0 ]]; then usage; fi

# array for our image paths
declare -a img_paths

# loop over directories to search non-recursively for images
for ((i=0; i<${#dirs[*]}; i++))
do
 set_img_paths "${dirs[$i]}" "-maxdepth 1"
done

# loop over directories to search recursively for images
for ((i=0; i<${#recursive_dirs[*]}; i++))
do
 set_img_paths "${recursive_dirs[$i]}" ""
done

# make sure we have some images
if [[ ${#img_paths[*]} -eq 0 ]]
then
 echo "Error: could not find any images"
 exit 2
fi

# randomize our array
random_order=$(seq ${#img_paths[*]} | shuf)
i=0
for r in $random_order
do
 randomized[$i]=${img_paths[$r-1]}
 i=$(( $i + 1 ))
done

# write our background xml file to stdout
echo ""
for ((i=0; i<${#randomized[*]}; i++))
do
 img_path=${randomized[$i]}
 echo -n "
 
  ${static_time}
  ${img_path}
 
"
 
 # transition to next image, or, if we are showing the last image, transition back to first image
 [[ $(( $i + 1 )) -lt ${#randomized[*]} ]] && next_img=${randomized[$i+1]} || next_img=${randomized[0]}
 echo -n "
 
  ${transition_time}
  ${img_path}
  ${next_img}
 
"
done
echo ""