sudo / permissions (read & write)

[naens]

When trying to save when sudo permission is required, prompt sudo pwd.

Types of sudo:

1. On file open
   (a) file doesn't exist, no right to write directory
   (b) file exists, no right to read/write file
2. On file save
   (a) creating new file: no right to write to directory
   (b) file exists: no right to write file

What if no need for sudo, but no permission to read/write?