diff --git a/tarback.sh b/tarback.sh
index da691c9..56780e9 100755
--- a/tarback.sh
+++ b/tarback.sh
@@ -28,18 +28,18 @@ TARBACK_PLUGIN_SEARCH_PATH_DEFAULT="$(dirname "$0"):$XDG_DATA_HOME:$XDG_DATA_DIR
 TARBACK_REMOTE="${TARBACK_REMOTE:-$TARBACK_REMOTE_DEFAULT}"
 # maybe the command needs to be transformed before being passed to the
 # remote command, see _transform_ssh_command for an example
-TARBACK_TRANSFORM_REMOTE_COMMAND="${TARBACK_TRANSFORM_REMOTE_COMMAND:-$TARBACK_TRANSFORM_REMOTE_COMMAND_DEFAULT}"
-TARBACK_TRANSFORM_REMOTE_ARGUMENT_COMMAND="${TARBACK_TRANSFORM_REMOTE_ARGUMENT_COMMAND:-$TARBACK_TRANSFORM_REMOTE_ARGUMENT_COMMAND_DEFAULT}"
-TARBACK_TAR_CREATE_COMMAND="${TARBACK_TAR_CREATE_COMMAND:-$TARBACK_TAR_CREATE_COMMAND_DEFAULT}"
-TARBACK_TAR_CREATE_ALT_COMMAND="${TARBACK_TAR_CREATE_ALT_COMMAND:-$TARBACK_TAR_CREATE_ALT_COMMAND_DEFAULT}"
-TARBACK_TAR_CREATE_USE_ALT_COMMAND="${TARBACK_TAR_CREATE_USE_ALT_COMMAND:-$TARBACK_TAR_CREATE_USE_ALT_COMMAND_DEFAULT}"
-TARBACK_TAR_EXTRACT_COMMAND="${TARBACK_TAR_EXTRACT_COMMAND:-$TARBACK_TAR_EXTRACT_COMMAND_DEFAULT}"
-TARBACK_TAR_EXTRACT_ALT_COMMAND="${TARBACK_TAR_EXTRACT_ALT_COMMAND:-$TARBACK_TAR_EXTRACT_ALT_COMMAND_DEFAULT}"
-TARBACK_TAR_EXTRACT_USE_ALT_COMMAND="${TARBACK_TAR_EXTRACT_USE_ALT_COMMAND:-$TARBACK_TAR_EXTRACT_USE_ALT_COMMAND_DEFAULT}"
-TARBACK_COMPRESSION="${TARBACK_COMPRESSION:-$TARBACK_COMPRESSION_DEFAULT}"
-TARBACK_SPLIT="${TARBACK_SPLIT:-$TARBACK_SPLIT_DEFAULT}"
-TARBACK_MERGE="${TARBACK_MERGE:-$TARBACK_MERGE_DEFAULT}"
-TARBACK_PLUGIN_SEARCH_PATH="${TARBACK_PLUGIN_SEARCH_PATH:-$TARBACK_PLUGIN_SEARCH_PATH_DEFAULT}"
+_="${TARBACK_TRANSFORM_REMOTE_COMMAND:=$TARBACK_TRANSFORM_REMOTE_COMMAND_DEFAULT}"
+_="${TARBACK_TRANSFORM_REMOTE_ARGUMENT_COMMAND:=$TARBACK_TRANSFORM_REMOTE_ARGUMENT_COMMAND_DEFAULT}"
+_="${TARBACK_TAR_CREATE_COMMAND:=$TARBACK_TAR_CREATE_COMMAND_DEFAULT}"
+_="${TARBACK_TAR_CREATE_ALT_COMMAND:=$TARBACK_TAR_CREATE_ALT_COMMAND_DEFAULT}"
+_="${TARBACK_TAR_CREATE_USE_ALT_COMMAND:=$TARBACK_TAR_CREATE_USE_ALT_COMMAND_DEFAULT}"
+_="${TARBACK_TAR_EXTRACT_COMMAND:=$TARBACK_TAR_EXTRACT_COMMAND_DEFAULT}"
+_="${TARBACK_TAR_EXTRACT_ALT_COMMAND:=$TARBACK_TAR_EXTRACT_ALT_COMMAND_DEFAULT}"
+_="${TARBACK_TAR_EXTRACT_USE_ALT_COMMAND:=$TARBACK_TAR_EXTRACT_USE_ALT_COMMAND_DEFAULT}"
+_="${TARBACK_COMPRESSION:=$TARBACK_COMPRESSION_DEFAULT}"
+_="${TARBACK_SPLIT:=$TARBACK_SPLIT_DEFAULT}"
+_="${TARBACK_MERGE:=$TARBACK_MERGE_DEFAULT}"
+_="${TARBACK_PLUGIN_SEARCH_PATH:=$TARBACK_PLUGIN_SEARCH_PATH_DEFAULT}"
 TARBACK_PLUGIN_SEARCH_PATH="$(echo "$TARBACK_PLUGIN_SEARCH_PATH" | tr ':'  '\n')"
 
 _transform_split_name() {