Increase space between two directories from “ls”

You can use the ln tool to create a symbolic link:

ln -s /Users/user1/.bashrc /Users/user2/.bashrc

In this example you are creating a new link for user2 pointing back to the existing file in user1's directory. You may need to use sudo ln ... if the permissions are not set correctly.

Untested

find . -depth -print0 |
while IFS= read -d '' -r file; do
    dir=$(dirname "$file")
    base=$(basename "$file") 
    base=${base//[[:space:]]/_}         # change whitespace to underscores
    base=${base//[^[:alnum:]_.]/}       # delete any chars not alphanumeric _ .
    newname="$dir/$base"
    if [[ -e $newname ]]; then
        echo "'$newname' exists, not renaming '$file'"
    else
        echo mv "$file" "$newname"
    fi
done

If it looks OK, remove the "echo"

The key here is the "-depth" option to find. It will emit "./sub dir/file name" before "./sub dir". Otherwise if "./sub dir" is renamed to "./subdir", then you'll get a 'file not found' error when the while loops gets to "./sub dir/file name". Also, it means you don't need different logic for directories.

The "-print0" option to find and the busy-ness around the read command are to ensure filenames with spaces are handled properly.