There is a chmod command to set file permissions, but can I get file permissions in octal mode (such as 755) from the command line?
You can try
From the man page of stat,
File permissions in Linux can be displayed in octal format using Linux stat command.
Just press Ctrl+Alt+T on your keyboard to open Terminal. When it opens, Navigate to the directory where you want to find the file permissions in octal mode.
%A Access rights in human readable form
%a Access rights in octal
%n File name
As detailed here, you can create an alias