Functions can be defined by entering code on the command line, a feature not supported by Matlab. For example, you may type:
octave:1> function s = hello_string (to_who)
> ## Say hello
> if nargin<1, to_who = "World"; end
> s = ["Hello ",\
> to_who];
> endfunction
octave:2> hello_string ("Moon")
ans = Hello Moon