Multi-disk audio CD ripper script using VLC

rip.lua

--Rips an audio cd using VLC
--Tested on Arch Linux, may or may not work on other Unix systems
local outdir="out/Welcome-to-Night-Vale/Book"
local fout=outdir.."/Chapter-%04d.mp3"
local sessionLimit=math.huge

os.execute( "mkdir -vp "..outdir )

local dev="/dev/cdrom"
local offset=0
do
	local f=io.open'offset'
	if f then
		offset=assert(tonumber(f:read'*a'),"Invalid saved offset")
	end
	print('offset',offset)
end
local sessionI=1
local globalI=offset+sessionI
print('globalI',globalI)


local fcmd=[[
cvlc --cdda-track %s cdda://%s ':sout=#transcode{vcodec=none,acodec=mp3,channels=2}:std{access=file,mux=raw,dst=%s}' 'vlc://quit' 2>&1]]
--redirect stderr to stdout, there is no other way to read io.popen's errors on the fly

while sessionI<=sessionLimit do
	local out=fout:format( globalI )
	local cmd=fcmd:format( sessionI, dev, out )
	print( cmd )
	local vlcout=io.popen( cmd )
	local vlcInvalidTrack=false
	for line in vlcout:lines() do
		if line:match'invalid track number' then
			vlcInvalidTrack=true
			break
		end
	end
	if vlcInvalidTrack then
		--clean up
		os.execute( 'rm -v '.. out)
		break
	end
	sessionI, globalI = sessionI + 1, globalI + 1
end

os.execute 'echo End of CD. Please insert the next one! | festival --tts'

assert(io.open('offset','w')):write(globalI-1)