>I can use -perm parameter of find to find writable files but how can I
>find read-only files? thanks!

Read-only files are files that are not writable, so you first write an expression that matches writable files and then negate it:

find ! \( -perm -200 -o -perm -020 -o -perm -002 \)

Barry Margolin

find . ! -perm +0222