before update trigger salesforce code example

Example: before delete trigger in salesforce

trigger AccountTrigger on Account (before delete) 
{ 
   if(System.Trigger.IsDelete)
   { 
     for (Account acc : trigger.old)
  {
    if (String.isNotBlank(acc.Client_ID__c))
     { 
  acc.addError('You cannot delete This Account Please contact your Salesforce.com Administrator for assistance.');
     }
         } 
   }
 }