Add dependency check and improve error handling.

start.tmpl

@@ -2,16 +2,38 @@
 
 INSTALLATION_NAME='{INSTALLATION_NAME}'
 TAG='{TAG}'
+DEPENDENCIES='sed awk shuf dirname docker'
 
+conf_file="/etc/$INSTALLATION_NAME.conf"
 
-source "/etc/$INSTALLATION_NAME.conf"
+for cmd in $DEPENDENCIES; do
+    if ! command -v "$cmd" >/dev/null 2>&1;  then
+        echo "$INSTALLATION_NAME: no such command '$cmd'" >&2
+        exit 1
+    fi
+done
 
+## Read the target configuration file name
+# Can mention multiple files in one line seperated by space.
+# Setting the variable multiple times is the same as
+# when all values were set on one line delimited by a space.
+# The final configuration file is drawn randomly from the
+# resulting set of file.
+ovpn_configuration_file="$(sed -n '/^[^#]/ s/OVPN_CONFIGURATION_FILE[^=]*=//p' "$conf_file" | tr ' ' '\n')"
+ovpn_configuration_file="$(echo "$ovpn_configuration_file" | shuf -n1)"
+ovpn_configuration_file="$(echo "$ovpn_configuration_file" | awk '{if (substr($0, 1, 1) != "/") {print "/etc/openvpn/client/"$0} else {print $0}}')"
+ovpn_configuration_file_parent_dir="$(dirname "$ovpn_configuration_file")"
+echo "ovpn_configuration_file=$ovpn_configuration_file"
+if ! stat "$ovpn_configuration_file"; then
+    exit 1
+fi
 
 docker run -it --cap-add NET_ADMIN \
     -v /etc/passwd:/etc/passwd \
-    -v /etc/openvpn/client:/etc/openvpn/client \
+    -v "$ovpn_configuration_file_parent_dir:$ovpn_configuration_file_parent_dir" \
     -v "$HOME:$HOME" \
     -e OVPN_USER="$USER" \
     -e OVPN_HOME="$HOME" \
-    -e OVPN_CONFIGURATION_FILE="/etc/openvpn/client/$OVPN_CONFIGURATION_FILE" \
+    -e OVPN_CONFIGURATION_FILE="$ovpn_configuration_file" \
     "$TAG" sh
+