Allow passing arguments via environment variable

Signed-off-by: Christian König <ckoenig@posteo.de>

docker/Dockerfile

@@ -113,5 +113,3 @@ RUN addgroup -g 29 docker_audio && addgroup shairport-sync docker_audio && addgr
 
 # Remove anything we don't need.
 RUN rm -rf /lib/apk/db/*
-
-ENTRYPOINT [ "/init" ]

docker/README.md

@@ -31,11 +31,12 @@ $ docker run -d --restart unless-stopped --net host --device /dev/snd \
 
 ### Options
 
-Command line options will be passed to Shairport Sync. Here is an example:
+To pass command line options to Shairport Sync they need to be set with `-e ARG=`. Here is an example:
+
 ```
 $ docker run -d --restart unless-stopped --net host --device /dev/snd \
-    mikebrady/shairport-sync:latest \
-    -v --statistics -a DenSystem -d hw:0 -c PCM
+    -e ARG="-v --statistics -a DenSystem -d hw:0 -c PCM" \
+    mikebrady/shairport-sync:latest
 ```
 This will send audio to alsa hardware device `hw:0` and make use of the that device's mixer control called `PCM`. The service will be visible as `DenSystem` on the network.
 

docker/classic/Dockerfile

@@ -91,5 +91,3 @@ RUN addgroup -g 29 docker_audio && addgroup shairport-sync docker_audio && addgr
 
 # Remove anything we don't need.
 RUN rm -rf /lib/apk/db/*
-
-ENTRYPOINT [ "/init" ]

docker/classic/etc/s6-overlay/s6-rc.d/04-shairport-sync/run

@@ -4,4 +4,4 @@ while [ ! -f /var/run/avahi-daemon/pid ]; do
   sleep 1
 done
 echo "Starting shairport-sync"
-exec /usr/local/bin/shairport-sync
+exec /usr/local/bin/shairport-sync $ARG

docker/etc/s6-overlay/s6-rc.d/05-shairport-sync/run

@@ -4,4 +4,4 @@ while [ ! -f /var/run/avahi-daemon/pid ]; do
   sleep 1
 done
 echo "Starting shairport-sync"
-exec /usr/local/bin/shairport-sync
+exec /usr/local/bin/shairport-sync $ARG