diff --git a/.cargo/config.toml b/.cargo/config.toml
index c30d988..f470805 100644
--- a/.cargo/config.toml
+++ b/.cargo/config.toml
@@ -4,4 +4,11 @@ rustflags = ["-C", "link-arg=-fuse-ld=lld"] # sudo apt -y install lld
 
 [target.'cfg(target_os = "macos")']
 # For faster link times ($ brew install michaeleisel/zld/zld )
-rustflags = ["-C", "link-arg=-fuse-ld=/usr/local/bin/zld"]
\ No newline at end of file
+rustflags = ["-C", "link-arg=-fuse-ld=/usr/local/bin/zld"]
+
+# Run time env. vars. see main.rs for usage
+[env]
+FOO = "bar"
+XX = "42"
+PATH_TO_SOME_TOOL = { value = "bin/tool", relative = true }
+USERNAME = { value = "test_user", force = true }
\ No newline at end of file
diff --git a/.vscode/settings.json b/.vscode/settings.json
new file mode 100644
index 0000000..4c9aee3
--- /dev/null
+++ b/.vscode/settings.json
@@ -0,0 +1,6 @@
+{
+    "rust-analyzer.linkedProjects": [
+        "./Cargo.toml"
+    ],
+    "rust-analyzer.showUnlinkedFileNotification": false
+}
\ No newline at end of file
diff --git a/Cargo.toml b/Cargo.toml
index 8a5cf83..f7ebd08 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -56,6 +56,18 @@ clap = "4.0.32"
 [features]
 foo = [] # feature has no explicit dependencies
 
+# Todo: how to use them?
+# Compile time env. vars
+# To use at runtime, ss .cargo/config.toml
+[env]
+RUST_BACKTRACE="1"
+AA=1
+BB=true
+FOO = "bar"
+XX = 42
+PATH_TO_SOME_TOOL = { value = "bin/tool", relative = true }
+USERNAME = { value = "test_user", force = true }
+
 # # All workspace members should inherit these keys for package declarations.
 # [workspace.package]
 # authors = ["Aptos Labs <opensource@aptoslabs.com>"]
diff --git a/src/env.vars.rs b/src/env.vars.rs
new file mode 100644
index 0000000..4e5aa39
--- /dev/null
+++ b/src/env.vars.rs
@@ -0,0 +1,11 @@
+
+// Run time env. vars use
+// .cargo/config.toml
+// [env]
+// ...
+// see main.rs for usage
+
+// Todo
+// Compile time env. vars use
+// Cargo.toml
+// [env]
\ No newline at end of file
diff --git a/src/main.rs b/src/main.rs
index 5473cff..6b6a64d 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -13,6 +13,11 @@ mod closure;
 
 fn main() {
 
+    // 0) Use runtime env. vars. See [env] in Cargo.toml
+    let xx: i32 = env!("XX").parse().unwrap();
+	println!("xx: {:?}", xx);   // 42
+
+
     // 1) Minigrep ---------------------------------------------
     // Usage:
         // cargo r search-str file.txt
diff --git a/src/temp.rs b/src/temp.rs
index cb149e6..fccb258 100644
--- a/src/temp.rs
+++ b/src/temp.rs
@@ -5,3 +5,9 @@
 //     assert_eq!(32, 32);
 // }
 
+
+#[test]
+fn ex1_ww() {
+    // println!("xx: {:?}", xx);
+    assert_eq!(42, 42);
+}