1 files changed, 9 insertions, 2 deletions
diff --git a/src/run/mod.rs b/src/run/mod.rs
index c7414a8..e041066 100644
--- a/src/run/mod.rs
+++ b/src/run/mod.rs
@@ -305,7 +305,11 @@ impl Executor {
 impl parse::Expander for Executor {
     type Error = ExecError;
 
-    fn expand_var(&mut self, var: BString) -> Result<BString, Self::Error> {
+    fn expand_var(
+        &mut self,
+        var: BString,
+        default: Option<BString>,
+    ) -> Result<BString, Self::Error> {
         if var.is_empty() {
             return Err(ExecError::UnknownVariable(var));
         }
@@ -331,7 +335,10 @@ impl parse::Expander for Executor {
 
         match std::env::var_os(OsStr::from_bytes(&var)) {
             Some(val) => Ok(val.as_bytes().to_vec()),
-            None => Err(ExecError::UnknownVariable(var)),
+            None => match default {
+                Some(d) => Ok(d),
+                None => Err(ExecError::UnknownVariable(var)),
+            },
         }
     }