Add return value handling and some tests

Signed-off-by: Malhar Vora <mlvora.2010@gmail.com>

Author: vbmade2000

src/uu/kill/src/kill.rs

@@ -14,14 +14,26 @@ use uucore::{error::UResult, format_usage, help_about, help_usage};
 const ABOUT: &str = help_about!("kill.md");
 const USAGE: &str = help_usage!("kill.md");
 
-
 #[uucore::main]
 pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     let matches = uu_app().try_get_matches_from(args)?;
 
     if let Some(pids) = matches.get_many::<i32>("pid") {
         for pid in pids {
             unsafe { libc::kill(*pid, libc::SIGTERM) };
+
+            let err = std::io::Error::last_os_error().raw_os_error();
+            if let Some(err_no) = err {
+                match err_no {
+                    libc::EPERM => {
+                        eprintln!("bash: kill: ({pid}) - Operation not permitted");
+                    }
+                    libc::ESRCH => {
+                        eprintln!("bash: kill: ({pid}) - No such process");
+                    }
+                    _ => {}
+                }
+            }
         }
     }
 

tests/by-util/test_kill.rs

@@ -12,7 +12,7 @@ fn test_invalid_arg() {
 
 #[test]
 #[cfg(target_os = "linux")]
-fn test_non_number_pid() {
+fn test_non_numerical_pid() {
     let res = new_ucmd!().arg("xyz").run();
 
     let stdout = res.stdout_str();
@@ -21,3 +21,17 @@ fn test_non_number_pid() {
     assert!(stdout.trim().len() == 0);
     assert!(stderr.contains("invalid value 'xyz'"));
 }
+
+#[test]
+#[cfg(target_os = "linux")]
+fn test_pid_doesnt_exist() {
+    let non_existent_pid = "1234567890";
+    let res = new_ucmd!().arg(non_existent_pid).run();
+
+    let stdout = res.stdout_str();
+    let stderr = res.stderr_str();
+    let error_msg = format!("bash: kill: ({non_existent_pid}) - No such process");
+
+    assert!(stdout.trim().len() == 0);
+    assert!(stderr.contains(error_msg.as_str()));
+}