Linux - Replacing spaces in the file names

Question

I have a number of files in a folder, and I want to replace every space character in all file names with underscores. How can I achieve this?

Answer 1

What if you want to apply the replace task recursively? How would you do that?

Well, I just found the answer myself. Not the most elegant solution, (also tries to rename files that do not comply with the condition) but it works. (BTW, in my case I needed to rename the files with '%20', not with an underscore)

#!/bin/bash
find . -type d | while read N
do
     (
           cd "$N"
           if test "$?" = "0"
           then
               for file in *; do mv "$file" ${file// /%20}; done
           fi
     )
done