format: %c prints the first character of a string

src/uucore/src/lib/features/format/argument.rs

@@ -41,14 +41,7 @@ impl<'a, T: Iterator<Item = &'a FormatArgument>> ArgumentIter<'a> for T {
         match next {
             FormatArgument::Char(c) => *c,
             FormatArgument::Unparsed(s) => {
-                let mut chars = s.chars();
+                s.chars().next().unwrap_or('\0')
-                let Some(c) = chars.next() else {
-                    return '\0';
-                };
-                let None = chars.next() else {
-                    return '\0';
-                };
-                c
             }
             _ => '\0',
         }

tests/by-util/test_printf.rs

@@ -162,6 +162,14 @@ fn sub_char() {
         .stdout_only("the letter A");
 }
 
+#[test]
+fn sub_char_from_string() {
+    new_ucmd!()
+        .args(&["%c%c%c", "five", "%", "oval"])
+        .succeeds()
+        .stdout_only("f%o");
+}
+
 #[test]
 fn sub_num_int() {
     new_ucmd!()