[bash] convert filename from lower case to upper case

[bash] convert filename from lower to upper

#!/bin/bash
DIR="./leetcode"
for file_name in `ls ./leetcode`;
do
    new_file_name=`echo "$file_name" | tr '[:upper:]' '[:lower:]' `
    if [ "$file_name"x != "$new_file_name"x ]; then
        echo "mv $DIR/$file_name $DIR/$new_file_name"
        `mv $DIR/$file_name $DIR/$new_file_name`
    fi
done