0.File Permission Modes
Files have three kinds of permissions: read (r), write (w), execute (x). These are generally represented as in rwx.
This kind of syntax can be difficult to type and remember
so one often uses a shorthand which lets you set all the permissions in one step.
4 if read permission is desired.
2 if write permission is desired.
1 if execute permission is desired.
Thus 7 means read/write/execute, 6 means read/write, and 5 means read/execute.
When you apply this to the chmod command you have to give three digits for each degree of freedom, such as in
有三個檔案file-1, file-2, temp