Changing file permission the easy way

You change a file's permissions using the Unix command "chmod" (for "change mode").
The chmod command supports a handy shortcut for setting permissions: You express the permissions
you want as a three-digit number, like "644" or "755", with the first digit giving
the owner's permissions, the second digit giving the group permissions, and the last digit
giving the "everybody else" permissions. The numbers themselves are arrived at by simple addition,
using the following formula:

4 = read permission
2 = write permission
1 = execute permission