[Fontconfig] Catching sans-serif fonts

[ben.guillon]

Hi,

I'm trying to use the fc commands in order to have a list of fonts that  
are sans-serif fonts, or monospaced fonts. I've found that for monospaced  
font the command 'fc-list ":spacing=mono" family' does the trick, but i've  
no idea about how to select sans-serif fonts.

What I don't understand is that there's already a mechanism in font config  
files to associate a generic family like sans-serif alias to actual fonts.

How can I do that with command lines?

Regards,
BG