Cómo redimensionar muchas imagenes al mismo tiempo con resizeallimgs

¿nunca les ha pasado que quieren hacer muchas thumbnails en un directorio rapidamente desde un script? si es asi encontre uno que hace uso de image magick y funciona sensacional lo pego aqui para que todos lo podamos usar :)

    #!/bin/sh
    # Name: resizeallimgs
    # Purpose: resize all jpg or png images in present directory to another sized jpg
    # Written by: Rene
    # CopyLeft, 2005
    # Uses: convert and display commands from ImageMagick
    # Syntax: resizeallimgs -j OR -p OR resizeallimgs -h / --help for help
    # Example: resizeallimgs -j converts jpgs in directory to resized jpgs
    # Example: resizeallimgs -p converts pngs in directory to resized jpgs

    # provide help for this script
    function useage {
    echo -----------------------------------------
    echo useage: resizeallimgs -j"|"-p "("jpg or png")"
    echo help: resizeallimgs -h "/" resizeallimgs --help
    echo creates new jpg files in this directory called '<'filename'>'_thumb.jpg
    echo pre-existing images are not changed
    echo user prompted for WIDTH of thumbnail image - in pixels - Example: 200
    echo thumbnail is scaled proportionately to input dimension
    echo " "
    echo after resizing you can view a composite image of all resized images
    echo answer "'"y"'" or "'"n"'" "("without quotes")" to view a composite of resized images created in the directory
    echo Notes: can take some time to display a large number of images
    echo " right click on composite display to see next composite page if it exists"
    echo " composite display can be saved as a single image and more by left clicking on composite window"
    echo -----------------------------------------
    echo
    }

    if [ $1 = "-h" ]; then
    useage
    exit
    fi

    if [ $1 = "--help" ]; then
    useage
    exit
    fi

    echo "Enter the WIDTH of new images (ex:200)"
    read response

    if [ $1 = '-j' ]; then
    echo JPG images being resized
    ls -1 *.jpg | sed "s/\(.*\)\.jpg/\1.jpg \1_thumb.jpg/" |xargs -n 2 convert -resize $response -quality 100 -compress JPEG
    fi

    if [ $1 = '-p' ]; then
    echo PNG images being resized to JPGs
    ls -1 *.png | sed "s/\(.*\)\.png/\1.png \1_thumb.jpg/" |xargs -n 2 convert -resize $response -quality 100 -compress JPEG
    fi

    # Ask if user wants to view a composite of all new jpg images

    echo "Do you want to display all thumbnails created in this directory?(y/n)"
    read displayall
    if [ $displayall = "y" ]; then
    display 'vid:*_thumb.*'
    exit
    fi
    exit

este script se puede encontrar aqui: http://www.w-3productions.com/resizeallimgs y fue creado por Rene