With White or Black?
If Black, then pretty much any Pirc source
If White, then "An attacking repertoire for White" by FM (now IM) Sam Collins recommends Bg5 against both the Pirc and Modern. As well, the more recent "Chess Developments : The Pirc" by FM James Vigus has a detailed chapter dedicated to this line.
I recommend 'The Pirc Defense' by GM Chernin.
I used the modern to avoid this. 5.Qd2 is better than 5.f4 because White has the possibility of playing f4 while removing ...c5 from the equasion.
Black can try h6 and g5 but it's loose and White should have no problems with Black doing something like that anyway. There's 5...c6 but after 6.f4 Black is trying to take on that mass of pawns with tricks on the queenside. It's not easy to play either way imo.
I am white. My opponent plays the pirc with: 1. e4 d6 2.d4 Nf6 3.Nc3 g6. Here 4.Bg5 has benn played one time agianst him, with the game going 4.Bg5 Bg7 5.f4 0-0 6.Nf3?! c5. I wonder where could I improve this: 5.Qd2, 6.Qd2 or something else.
4...c6 was recommended in the first and only Pirc book I have owned, the Smith & Hall one. The idea is to refrain from ..Bg7. Not sure how well this idea holds up today.
The Left Hook Austrian is all right. I have played it before. I discovered that 5...O-O 6.Bd3 is weak due to ..e5! which equalizes pretty much immediately. White just has to play Nf3 anyway and it gets back into a normal position. (albeit one where White's avoided the ..c5 sharp lines)
Black can also play ironically with 5...c5 6.dxc5 Qa5 7.b4 Qc7 as a gambit, trying to show that White's long diagonal is now loose. White can get an advantage, but you have to know the line, don't just take for granted that ..c5 is prevented!
It's called the Byrne Attack as far as I know.
Any article/source where I can study this or analysis??