diff --git a/tarback/docker.sh b/tarback/docker.sh
index eb8d02a..f8a748b 100644
--- a/tarback/docker.sh
+++ b/tarback/docker.sh
@@ -1,8 +1,8 @@
 #!/bin/sh
 
-_tarback_plugin_docker_use_container=false
+_tarback_plugin_docker_use_container=
 
-short_options='c'
+short_options='c:'
 while getopts "$short_options" arg; do
     case "$arg" in
         c)
@@ -11,13 +11,12 @@ while getopts "$short_options" arg; do
     esac
 done
 
-if "$_tarback_plugin_docker_use_container"; then
-    _tarback_plugin_docker_cmd='docker exec -i "$1" '
+if [ -n "$_tarback_plugin_docker_use_container" ]; then
+    _tarback_plugin_docker_cmd="docker exec -i '$_tarback_plugin_docker_use_container' "
     TARBACK_TAR_CREATE_COMMAND="$_tarback_plugin_docker_cmd $TARBACK_TAR_CREATE_COMMAND"
     TARBACK_TAR_EXTRACT_COMMAND="$_tarback_plugin_docker_cmd $TARBACK_TAR_EXTRACT_COMMAND"
 else
     _tarback_plugin_docker_cmd='docker run -i --rm --workdir=/mnt --volume="$1":/mnt/"$1" alpine '
-
     TARBACK_TAR_CREATE_COMMAND="$_tarback_plugin_docker_cmd $(echo "$TARBACK_TAR_CREATE_COMMAND" | sed 's_$1_/mnt/$1_g')"
     TARBACK_TAR_EXTRACT_COMMAND="$_tarback_plugin_docker_cmd $(echo "$TARBACK_TAR_EXTRACT_COMMAND" | sed 's_$1_/mnt/$1_g')"
 fi