SQL Server 2008 - create database script (schema + data) with command-line

The graphical tool is just a wrapper around the SMO classes that actually implement scripting, like the Scripter class. There is an example of scripting all tables in a database with SMO in MSDN: Scripting:

//Connect to the local, default instance of SQL Server. 
{ 
   Server srv = default(Server); 
   srv = new Server(); 
   //Reference the AdventureWorks database. 
   Database db = default(Database); 
   db = srv.Databases("AdventureWorks"); 
   //Define a Scripter object and set the required scripting options. 
   Scripter scrp = default(Scripter); 
   scrp = new Scripter(srv); 
   scrp.Options.ScriptDrops = false; 
   scrp.Options.WithDependencies = true; 
   //Iterate through the tables in database and script each one. Display the script. 
   //Note that the StringCollection type needs the System.Collections.Specialized namespace to be included. 
   Table tb = default(Table); 
   Urn[] smoObjects = new Urn[2]; 
   foreach ( tb in db.Tables) { 
      smoObjects = new Urn[1]; 
      smoObjects(0) = tb.Urn; 
      if (tb.IsSystemObject == false) { 
         StringCollection sc = default(StringCollection); 
         sc = scrp.Script(smoObjects); 
         string st = null; 
         foreach ( st in sc) { 
            Console.WriteLine(st); 
         } 
      } 
   } 
} 

There are many more examples how to use it on various other sites.