echo: add support for \NNN octal escape sequence

src/uu/echo/src/echo.rs

@@ -54,6 +54,16 @@ fn print_escaped(input: &str, mut output: impl Write) -> io::Result<bool> {
             continue;
         }
 
+        // This is for the \NNN syntax for octal sequences.
+        // Note that '0' is intentionally omitted because that
+        // would be the \0NNN syntax.
+        if let Some('1'..='8') = iter.peek() {
+            if let Some(parsed) = parse_code(&mut iter, 8, 3) {
+                write!(output, "{parsed}")?;
+                continue;
+            }
+        }
+
         if let Some(next) = iter.next() {
             let unescaped = match next {
                 '\\' => '\\',

tests/by-util/test_echo.rs

@@ -253,3 +253,30 @@ fn wrapping_octal() {
         .succeeds()
         .stdout_is("A\n");
 }
+
+#[test]
+fn old_octal_syntax() {
+    new_ucmd!()
+        .arg("-e")
+        .arg("\\1foo")
+        .succeeds()
+        .stdout_is("\x01foo\n");
+
+    new_ucmd!()
+        .arg("-e")
+        .arg("\\43foo")
+        .succeeds()
+        .stdout_is("#foo\n");
+
+    new_ucmd!()
+        .arg("-e")
+        .arg("\\101foo")
+        .succeeds()
+        .stdout_is("Afoo\n");
+
+    new_ucmd!()
+        .arg("-e")
+        .arg("\\1011")
+        .succeeds()
+        .stdout_is("A1\n");
+}