Bio3D is a package written for the R platform. Details are in thegrantlab.org/bio3d/index.php
library(bio3d, lib.loc = "~/R")
library(bio3d, lib.loc = "~/R")
pdb < - read.pdb("File.pdb")
atom.select(pdb,"calpha")$atom ---- Gives the atom index of all alpha carbons
pdb$atom$resid -- Gives the residue ID of all atoms
pdb$atom$resid(atom.select(pdb,"calpha")$atom) --- Combines the two