adjust_size convenience function

gistfile1.sh

adjust_size() {
    size=$1
    shift

    if [ "x" = "x$size" -o -f "$size" ]; then
        echo "Usage: adjust_size size_spec file [file2 [file3...]]"
        return 1
    fi

    for P in "$@"; do
        O="${P%\.*}-$size.${P##*\.}"
        if [ -e "$O" ]; then
            echo "Info: '$O' already exists, skipping.";
            continue
        fi
        convert "$P" -resize $size -rotate 0 "$O"
    done
}