From 519893d31f0118cbc57e26ddf87255f00bfc366c Mon Sep 17 00:00:00 2001
From: Tim Ledbetter <timledbetter@gmail.com>
Date: Thu, 15 Jun 2023 18:25:05 +0100
Subject: [PATCH] pkill: Add `-n` option to kill the newest matching process
 only

---
 Base/usr/share/man/man1/pkill.md |  3 ++-
 Userland/Utilities/pkill.cpp     | 21 +++++++++++++++------
 2 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/Base/usr/share/man/man1/pkill.md b/Base/usr/share/man/man1/pkill.md
index dc40e5847c6..7f3e2fa0f61 100644
--- a/Base/usr/share/man/man1/pkill.md
+++ b/Base/usr/share/man/man1/pkill.md
@@ -5,7 +5,7 @@ pkill - Signal processes based on name
 ## Synopsis
 
 ```sh
-$ pkill [--count] [--ignore-case] [--echo] [--signal signame] [--uid uid-list] [--exact] <process-name>
+$ pkill [--count] [--ignore-case] [--echo] [--newest] [--signal signame] [--uid uid-list] [--exact] <process-name>
 ```
 
 ## Options
@@ -13,6 +13,7 @@ $ pkill [--count] [--ignore-case] [--echo] [--signal signame] [--uid uid-list] [
 * `-c`, `--count`: Display the number of matching processes
 * `-i`, `--ignore-case`: Make matches case-insensitive
 * `-e`, `--echo`: Display what is killed
+* `-n`, `--newest`: Kill the most recently created process only
 * `-s signame`, `--signal signame`: Signal to send. The signal name or number may be used
 * `-U uid-list`, `--uid uid-list`: Select only processes whose UID is in the given comma-separated list. Login name or numerical user ID may be used
 * `-x`, `--exact`: Select only processes whose names match the given pattern exactly
diff --git a/Userland/Utilities/pkill.cpp b/Userland/Utilities/pkill.cpp
index 6b95dedabfd..926857ad75b 100644
--- a/Userland/Utilities/pkill.cpp
+++ b/Userland/Utilities/pkill.cpp
@@ -6,6 +6,7 @@
  */
 
 #include <AK/Format.h>
+#include <AK/QuickSort.h>
 #include <AK/Vector.h>
 #include <LibCore/Account.h>
 #include <LibCore/ArgsParser.h>
@@ -29,6 +30,7 @@ ErrorOr<int> serenity_main(Main::Arguments args)
     bool case_insensitive = false;
     bool echo = false;
     bool exact_match = false;
+    bool newest_only = false;
     StringView pattern;
     HashTable<uid_t> uids_to_filter_by;
     int signal = SIGTERM;
@@ -37,6 +39,7 @@ ErrorOr<int> serenity_main(Main::Arguments args)
     args_parser.add_option(display_number_of_matches, "Display the number of matching processes", "count", 'c');
     args_parser.add_option(case_insensitive, "Make matches case-insensitive", "ignore-case", 'i');
     args_parser.add_option(echo, "Display what is killed", "echo", 'e');
+    args_parser.add_option(newest_only, "Kill the most recently created process only", "newest", 'n');
     args_parser.add_option(Core::ArgsParser::Option {
         .argument_mode = Core::ArgsParser::OptionArgumentMode::Required,
         .help_string = "Signal number to send. A signal name or number may be used",
@@ -115,12 +118,18 @@ ErrorOr<int> serenity_main(Main::Arguments args)
         }
     }
 
-    for (auto& process : matched_processes) {
-        auto result = Core::System::kill(process.pid, signal);
-        if (result.is_error())
-            warnln("Killing pid {} failed. {}", process.pid, result.release_error());
-        else if (echo)
-            outln("{} killed (pid {})", process.name, process.pid);
+    if (!matched_processes.is_empty()) {
+        quick_sort(matched_processes, [](auto const& a, auto const& b) { return a.creation_time < b.creation_time; });
+        if (newest_only)
+            matched_processes = { matched_processes.last() };
+
+        for (auto& process : matched_processes) {
+            auto result = Core::System::kill(process.pid, signal);
+            if (result.is_error())
+                warnln("Killing pid {} failed. {}", process.pid, result.release_error());
+            else if (echo)
+                outln("{} killed (pid {})", process.name, process.pid);
+        }
     }
 
     if (display_number_of_matches)