Whenever you create a file as a normal user, by default, it will have read/write permissions for the user and group, and read permission for others.

chmod u+x donnie_script.sh
chmod g+x donnie_script.sh
chmod o+x donnie_script.sh
chmod u+x,g+x donnie_script.sh
chmod a+x donnie_script.sh

The first three commands add the executable permission for the user, the group, and others. The fourth command adds executable permissions for both the user and the group, while the last command adds executable permissions for everybody (a for all). You can also remove the executable permissions by replacing + with -. Finally, you can also add or remove the read or write permissions, as appropriate.

While this method can be handy at times, it also has a bit of a flaw; that is, it can only add permissions to what's already there, or remove permissions from what's already there. If you need to ensure that all of the permissions for a particular file get set to a certain value, the symbolic method can get a bit unwieldy. And for shell scripting, forget about it. In a shell script, you'd need to add all kinds of extra code just to determine which permissions have already been set. The numerical method can vastly simplify things for us.