allow setting user flag at runtime

entrypoint.sh

@@ -1,17 +1,29 @@
 #!/bin/bash
 
+# if non-root user specified at runtime with user flag, just execute CMD and exit
+if [ $(id -u) -ne 0 ]; then
+  exec "$@"
+  return
+fi
+
 # OUID and OGID are the original user and group ids set during the image
 # build and are replaced here at runtime if PGID and PUID are set
-if [ -n "$PGID" ] && [ "$PGID" -ne 0 ]; then
-  sed -i "s/nonroot:x:$OUID:$OGID:/nonroot:x:$OUID:$PGID:/" /etc/passwd
-  sed -i "s/nonroot:x:$OGID:/nonroot:x:$PGID:/" /etc/group
+if [ -n "$PGID" ] && [ "$PGID" -ne 0 ] && [ "$PGID" -ne "$OGID" ] ; then
+  # if group id doesn't already exist, set nonroot gid = $PGID, otherwise just use existing group name for $PGID
+  if ! grep ":x:$PGID:" /etc/group 2>&1 >/dev/null; then
+    sed -i "s/nonroot:x:$OUID:$OGID:/nonroot:x:$OUID:$PGID:/" /etc/passwd
+    sed -i "s/nonroot:x:$OGID:/nonroot:x:$PGID:/" /etc/group
+  fi
 fi
 
-if [ -n "$PUID" ] && [ "$PUID" -ne 0 ]; then
-  sed -i "s/nonroot:x:$OUID:/nonroot:x:$PUID:/" /etc/passwd
+if [ -n "$PUID" ] && [ "$PUID" -ne 0 ] && [ "$PUID" -ne "$OUID" ]; then
+  # if user id doesn't already exist, set nonroot uid = $PUID, otherwise just use existing username for $PUID
+  if ! grep ":x:$PUID:" /etc/passwd 2>&1 >/dev/null; then
+    sed -i "s/nonroot:x:$OUID:/nonroot:x:$PUID:/" /etc/passwd
+  fi
 fi
 
-chown nonroot: /app /app/*
+chown $PUID:$PGID /app /app/*
 
 # Use su-exec to execute the command as nonroot user
-exec su-exec nonroot "$@"
+exec su-exec $PUID:$PGID "$@"