diff --git a/01_phase_rust_src/sv/src/main.rs b/01_phase_rust_src/sv/src/main.rs
index 20097a0..944a2f1 100644
--- a/01_phase_rust_src/sv/src/main.rs
+++ b/01_phase_rust_src/sv/src/main.rs
@@ -7,6 +7,18 @@ use std::env;
 fn main() {
     let args: Vec<String> = env::args().collect();
 
+    // def env variables.
+    let svdir_env = env::var("SVDIR");
+    //let svwait_env = env::var("SVWAIT");
+
+    let svdir_var = match svdir_env {
+        Ok(var) => var,
+        Err(..) => "/run/runit/service".to_string(),
+    };
+
+    dbg!(svdir_var);
+
+
     // args
     let arg_parser: Vec<String> = parser::parse_args(args);