ffmpeg: loop a playlist forever using concat demuxer for icecast server

A.txt

ffconcat version 1.0
file 'A'
file 'B.txt'

B.txt

ffconcat version 1.0
file 'B'
file 'A.txt'

radio.sh

#!/bin/bash

SERVER="icecast://source:[email protected]:8000/stream"
ffmpeg \
    -stream_loop -1 \
    -re \
    -f concat -i "A.txt" \
    -ignore_unknown -err_detect ignore_err \
    -c:a libmp3lame -b:a 128k -f mp3 -content_type audio/mpeg      ${SERVER}.mp3 \
    -c:a libvorbis  -b:a 128k -f ogg -content_type application/ogg ${SERVER}.ogg 

the files A and B are symbolic links to another audio, to change it:

rm A && ln -s "/path/audio01.mp3"
rm B && ln -s "/path/audio02.mp3"

How to known what file is playing:

fuser A
fuser B