From 0ba9a301b0db81a1c98e34184315c51c18dddf57 Mon Sep 17 00:00:00 2001
From: Joseph Jon Booker <joe@neoturbine.net>
Date: Mon, 25 Mar 2024 22:03:26 -0500
Subject: [PATCH] expr: fix panic for "empty substitution" test case

---
 src/uu/expr/src/syntax_tree.rs | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/uu/expr/src/syntax_tree.rs b/src/uu/expr/src/syntax_tree.rs
index 30d50fb26..d333e6c2f 100644
--- a/src/uu/expr/src/syntax_tree.rs
+++ b/src/uu/expr/src/syntax_tree.rs
@@ -148,7 +148,7 @@ impl StringOp {
                 .map_err(|_| ExprError::InvalidRegexExpression)?;
                 Ok(if re.captures_len() > 0 {
                     re.captures(&left)
-                        .map(|captures| captures.at(1).unwrap())
+                        .and_then(|captures| captures.at(1))
                         .unwrap_or("")
                         .to_string()
                 } else {
@@ -609,4 +609,14 @@ mod test {
             Err(ExprError::ExpectedClosingBraceInsteadOf("a".to_string()))
         );
     }
+
+    #[test]
+    fn empty_substitution() {
+        // causes a panic in 0.0.25
+        let result = AstNode::parse(&["a", ":", r"\(b\)*"])
+            .unwrap()
+            .eval()
+            .unwrap();
+        assert_eq!(result.eval_as_string(), "");
+    }
 }