add new parameter "group" to filter alert rules

README.md

@@ -155,6 +155,9 @@ Flags:
   -n, --name strings               The name of one or more specific alerts to check.
                                    This parameter can be repeated e.G.: '--name alert1 --name alert2'
                                    If no name is given, all alerts will be evaluated
+  -g, --group strings              The name of one or more specific groups to check.
+                                   This parameter can be repeated e.G.: '--group group1 --group group2'
+                                   If no group is given, all groups will be scanned for alerts
   -T, --no-alerts-state string     State to assign when no alerts are found (0, 1, 2, 3, OK, WARNING, CRITICAL, UNKNOWN). If not set this defaults to OK (default "OK")
   -P, --problems                   Display only alerts which status is not inactive/OK. Note that in combination with the --name flag this might result in no alerts being displayed
 ```

cmd/alert.go

@@ -83,7 +83,7 @@ inactive = 0`,
 		}
 
 		// Get all rules from all groups into a single list
-		rules := alert.FlattenRules(alerts.Groups)
+		rules := alert.FlattenRules(alerts.Groups, cliAlertConfig.Group)
 
 		// If there are no rules we can exit early
 		if len(rules) == 0 {
@@ -217,6 +217,11 @@ func init() {
 			"\nThis parameter can be repeated e.G.: '--name alert1 --name alert2'"+
 			"\nIf no name is given, all alerts will be evaluated")
 
+	fs.StringSliceVarP(&cliAlertConfig.Group, "group", "g", nil,
+		"The name of one or more specific groups to check for alerts."+
+			"\nThis parameter can be repeated e.G.: '--group group1 --group group2'"+
+			"\nIf no group is given, all groups will be scanned for alerts")
+
 	fs.BoolVarP(&cliAlertConfig.ProblemsOnly, "problems", "P", false,
 		"Display only alerts which status is not inactive/OK. Note that in combination with the --name flag this might result in no alerts being displayed")
 }