I belong to a liberal community and what I have seen, when somebody is in mourning for a parent, is that they wear a "kriah ribbon" instead of tearing an actual garment, and they wear it at least through the period of shiva (I can't remember if they wear it through sh'loshim). I am fortunate to not yet have direct experience in this area, nor have I learned the relevant laws, but a recent question here about that "ribbon" practice made me wonder what the traditional practice really is. (I am aware of the problems with the ribbon practice, which is why I want to know what's correct.)
I know that upon learning of the death one tears his shirt. Does the mourner do it that one time -- the commandment is to tear -- or does he wear a torn garment for some period of time to show that he is in mourning? If the latter, how long? Does he keep wearing the same shirt, or if he changes clothes (as we are more wont to do in modern times) does he tear the other ones too?