busy can properly exit, pattern can not inject code

profile.d/fun.sh

@@ -88,19 +88,23 @@ busy()
         esac
     done
 
-    # If a pattern was provided as a positional argument (e.g., 'busy "ff 00"'),
-    # it is captured here.
-    [[ -n "$1" ]] && pattern="$1"
-
     # Convert milliseconds to seconds for 'sleep'
-    local delay_s=$(awk "BEGIN { printf \"%.3f\", $delay_ms / 1000 }")
+    local delay_s=$(awk "BEGIN{
+        printf \"%.3f\", $delay_ms / 1000 }")
 
     # Monitor /dev/urandom
-    cat /dev/urandom | hexdump -C | grep --line-buffered "$pattern" | \
+    (
+        hexdump -C < /dev/urandom | grep -iF --line-buffered "$pattern" | \
             while read -r line; do
                 echo "$line"
                 [[ $delay_ms -gt 0 ]] && sleep "$delay_s"
             done
+    ) & local sub_pid=$!
+
+    IFS= read -r -n 1 -s _ </dev/tty
+    kill -- -"$sub_pid" 2>/dev/null || kill "$sub_pid" 2>/dev/null
+    wait "$sub_pid" 2>/dev/null
+    return 0
 }
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