Femtosecond laser pulses with powers below the blowup threshold for self-focused beams are shown to experience spatial self-action in hollow-core photonic crystal fibers filled with argon, nitrogen, and atmospheric air. Regardless of the transverse field distribution at the input of the fiber, the output beam pattern in this regime tends to a circularly symmetric profile, corresponding to a ground-state waveguide induced by laser pulses inside a hollow fiber.