I mean to set the default legend font size (and other properties as well) in my Octave script.
Both set (activated separately)
legend_fontsize = 14;
set(0, "defaultlegendlocation", "northoutside");
set(0, "defaultlegendfontsize", legend_fontsize);
produce error: invalid default property specification.
What is the correct syntax?
In Matlab, this suggests it should not throw any error, and it should possibly work.
In theory you are right that this should also work in octave, since according to the manual, octave supports the same syntax, for all kinds of graphical object 'types'.
However, legend is a special case, because it is not implemented as its own graphical object 'type' in octave; instead, as stated in the documentation:
A legend is implemented as an additional axes object with the 'tag'
property set to "legend". Properties of the legend object may be
manipulated directly by using 'set'.
Therefore, this means that the defaultlegendfontsize strategy won't work.
It also means that, since in principle a 'legend' object is an 'axes' object in disguise, set( 0, 'defaultaxesfontsize', 30 ) will work ... but obviously with unintended consequences affecting all axes objects.
You could point that out in the octave bug tracker if you'd like.
In the meantime, you could always do something like the following in your .octaverc as a workaround:
function h = legend( varargin )
% Wrapper to builtin legend function, also setting font to default size of 30
h = builtin( 'legend', varargin{:} )
set( h, 'fontsize', 30 )
endfunction
This effectively shadows the builtin 'legend' command with a custom one, that applies 'default' values as an extra step before returning the handle.
PS: Having said this, one needs to be careful with setting such defaults, in the case of code dissemination and re-use which assumes such defaults are preset in all environments.
This is a common point of caution in R users against creating elaborate .Rprofile files, for instance.
PS 2: Alternatively, a nice approach when you have lots of defaults to apply would be to create a function applydefaults( handle ) which applies all your preferences in one go, and call it at the end of whatever object you want to apply these to. This is what I used to do in my thesis. It may sound like slightly more effort, but you end up thanking yourself 1 month down the line when it's 100% clear what is happening and where the formatting changes came from!