snice: implement --no-action

src/uu/snice/src/action.rs

@@ -111,7 +111,7 @@ impl Display for ActionResult {
 ///
 /// But we don't know if the process of pid are exist, if [None], the process doesn't exist
 #[cfg(target_os = "linux")]
-fn set_priority(pid: u32, prio: &Priority) -> Option<ActionResult> {
+fn set_priority(pid: u32, prio: &Priority, take_action: bool) -> Option<ActionResult> {
     use libc::{getpriority, setpriority, PRIO_PROCESS};
     use nix::errno::Errno;
 
@@ -136,6 +136,10 @@ fn set_priority(pid: u32, prio: &Priority) -> Option<ActionResult> {
         prio
     };
 
+    if !take_action {
+        return Some(ActionResult::Success);
+    }
+
     let prio = match prio {
         Priority::Increase(prio) => current_priority + *prio as i32,
         Priority::Decrease(prio) => current_priority - *prio as i32,
@@ -159,11 +163,15 @@ fn set_priority(pid: u32, prio: &Priority) -> Option<ActionResult> {
 
 // TODO: Implemented this on other platform
 #[cfg(not(target_os = "linux"))]
-fn set_priority(_pid: u32, _prio: &Priority) -> Option<ActionResult> {
+fn set_priority(_pid: u32, _prio: &Priority, _take_action: bool) -> Option<ActionResult> {
     None
 }
 
-pub(crate) fn perform_action(pids: &[u32], prio: &Priority) -> Vec<Option<ActionResult>> {
-    let f = |pid: &u32| set_priority(*pid, prio);
+pub(crate) fn perform_action(
+    pids: &[u32],
+    prio: &Priority,
+    take_action: bool,
+) -> Vec<Option<ActionResult>> {
+    let f = |pid: &u32| set_priority(*pid, prio, take_action);
     pids.iter().map(f).collect()
 }

src/uu/snice/src/snice.rs

@@ -173,9 +173,10 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     }
 
     // Case1: Perform priority
+    let take_action = !matches.get_flag("no-action");
     if let Some(targets) = settings.expressions {
         let pids = collect_pids(&targets);
-        let results = perform_action(&pids, &settings.priority);
+        let results = perform_action(&pids, &settings.priority, take_action);
 
         if results.iter().all(|it| it.is_none()) || results.is_empty() {
             return Err(USimpleError::new(1, "no process selection criteria"));
@@ -184,6 +185,8 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
         if settings.verbose {
             let output = construct_verbose_result(&pids, &results).trim().to_owned();
             println!("{output}");
+        } else if !take_action {
+            pids.iter().for_each(|pid| println!("{pid}"));
         }
     }
 
@@ -255,7 +258,7 @@ pub fn uu_app() -> Command {
             // arg!(-i --interactive   "interactive"),
             arg!(-l --list                  "list all signal names"),
             arg!(-L --table                 "list all signal names in a nice table"),
-            // arg!(-n --"no-action"   "do not actually kill processes; just print what would happen"),
+            arg!(-n --"no-action"   "do not actually kill processes; just print what would happen"),
             arg!(-v --verbose               "explain what is being done"),
             // arg!(-w --warnings      "enable warnings (not implemented)"),
             // Expressions