hostname: fix -d flag (#8657)

* hostname: fix -d flag

* tests/hostname: test -d when no domain

src/uu/hostname/src/hostname.rs

@@ -177,8 +177,10 @@ fn display_hostname(matches: &ArgMatches) -> UResult<()> {
                 } else {
                     println!("{}", &hostname[ci.0 + 1..]);
                 }
-                return Ok(());
+            } else if matches.get_flag(OPT_SHORT) {
+                println!("{hostname}");
             }
+            return Ok(());
         }
 
         println!("{hostname}");

tests/by-util/test_hostname.rs

@@ -37,3 +37,16 @@ fn test_hostname_full() {
 fn test_invalid_arg() {
     new_ucmd!().arg("--definitely-invalid").fails_with_code(1);
 }
+
+#[test]
+fn test_hostname_domain_empty() {
+    let fqdn = new_ucmd!().arg("-f").succeeds();
+    let short = new_ucmd!().arg("-s").succeeds();
+    let domain = new_ucmd!().arg("-d").succeeds();
+    let domain_short = new_ucmd!().arg("-sd").succeeds();
+
+    if fqdn.stdout() == short.stdout() {
+        assert!(domain.stdout().is_empty());
+        assert!(domain_short.stdout().is_empty());
+    }
+}