Hi!
As far as I'm aware, there is no direct way to get output from your shader code to your console (remember that GLSL code is running several thousand times a second in parallel on your GPU, there's no way you could evaluate the amount of output that would generate), however, you can "cheat" a little by putting the information you want to output into the color the shader puts out.
There's two ways of doing this, one is making a condition that you want to check (say angle < 0.5) and then, if that condition is true, just set gl_fragment_color to an easily recognizble value (vec4(1, 0, 0, 1) = bright red for example). This can show you, where on your screen a certain condition holds.
The other way is just outputting variables directly into your color (by e.g. using gl_fragment_color = vexc4(angle, 0, 0, 1)) and using a screen-capture tool in combination with any painting tool or color-picker to read the exact values of variables from your screen.
These can really help with debugging GLSL code, even if they may seem a bit convoluted. ;)
Hope that helps a bit!
LG,
Jonathan