better error handling (again)

README.md

@@ -11,7 +11,12 @@ i have an unhealthy relationship with overlayfs. i also like to easily change my
 # Usage
 
 ```sh
-configctl [OPTIONS] <changeset> [unmount]
+configctl [OPTIONS] <changeset_name> [unmount]
+
+options
+  -a, --automount      automatically enable the changeset service file
+  -f, --force          ovewrite existing service file
+  -s, --service-path   the path to write the service file
 ```
 
 by default, the configctl expects the base configuration set to exist in `$XDG_DATA_HOME/config/base` (usually `~/.local/share/config/base`) and the changesets to exist in `$XDG_DATA_HOME/config/changeset`. changes while the configuration is mounted will be written to `$XDG_STATE_HOME/config/{<changeset>,.work_<changeset>}`

configctl

@@ -60,6 +60,11 @@ CHANGESET="$CHANGESET_DIR/$SELECTED"
 UPPER_DIR="$XDG_STATE_HOME/config/$SELECTED"
 WORKDIR="$XDG_STATE_HOME/config/.work_$SELECTED"
 
+if [ -z "$SELECTED" ]; then
+  usage
+  exit
+fi
+
 if [ ! -d "$CHANGESET" ]; then
   echo "'$CHANGESET' not found."
   exit 1