expr: Escape '$' characters

Author: frendsick

src/uu/expr/src/syntax_tree.rs

@@ -182,6 +182,13 @@ impl StringOp {
                             ('\\', false) => re_string.push(curr),
                             _ => re_string.push_str(r"\^"),
                         },
+                        '$' => {
+                            if prev_is_escaped || prev != '\\' {
+                                re_string.push_str(r"\$");
+                            } else {
+                                re_string.push('$');
+                            }
+                        }
                         _ => re_string.push(curr),
                     }
 

tests/by-util/test_expr.rs

@@ -770,7 +770,6 @@ mod gnu_expr {
             .stdout_only("3\n");
     }
 
-    #[ignore]
     #[test]
     fn test_bre11() {
         new_ucmd!()