From cae94028afcfa19b78dfc1072d1a22d8b2c6ca38 Mon Sep 17 00:00:00 2001
From: Sylvestre Ledru <sylvestre@debian.org>
Date: Thu, 18 Dec 2025 21:46:52 +0100
Subject: [PATCH] kill -1 should trigger an error

https://github.com/uutils/coreutils/issues/9699
---
 src/uu/kill/src/kill.rs    |  4 ++--
 tests/by-util/test_kill.rs | 24 ++++++++++++++++++++++++
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/src/uu/kill/src/kill.rs b/src/uu/kill/src/kill.rs
index 809d59b7d..94aa81964 100644
--- a/src/uu/kill/src/kill.rs
+++ b/src/uu/kill/src/kill.rs
@@ -137,8 +137,8 @@ pub fn uu_app() -> Command {
 }
 
 fn handle_obsolete(args: &mut Vec<String>) -> Option<usize> {
-    // Sanity check
-    if args.len() > 2 {
+    // Sanity check - need at least the program name and one argument
+    if args.len() >= 2 {
         // Old signal can only be in the first argument position
         let slice = args[1].as_str();
         if let Some(signal) = slice.strip_prefix('-') {
diff --git a/tests/by-util/test_kill.rs b/tests/by-util/test_kill.rs
index 5fb8fb312..aad1982d6 100644
--- a/tests/by-util/test_kill.rs
+++ b/tests/by-util/test_kill.rs
@@ -395,3 +395,27 @@ fn test_kill_with_signal_and_table() {
         .arg("-t")
         .fails();
 }
+
+/// Test that `kill -1` (signal without PID) reports "no process ID" error
+/// instead of being misinterpreted as pid=-1 which would kill all processes.
+/// This matches GNU kill behavior.
+#[test]
+fn test_kill_signal_only_no_pid() {
+    // Test with -1 (SIGHUP)
+    new_ucmd!()
+        .arg("-1")
+        .fails()
+        .stderr_contains("no process ID specified");
+
+    // Test with -9 (SIGKILL)
+    new_ucmd!()
+        .arg("-9")
+        .fails()
+        .stderr_contains("no process ID specified");
+
+    // Test with -TERM
+    new_ucmd!()
+        .arg("-TERM")
+        .fails()
+        .stderr_contains("no process ID specified");
+}