new gate;
public OnGameModeInit( )
{
    gate = F_CreateObject( .... )
    return 1;
}

public OnPlayerCommandText( playerid, cmdtext[ ] )
{
    if( !strcmp( cmdtext, "/open", true ) )
    {
        F_MoveObject ( gate, coordinates where the gate moves ( example 0.0, 0.0, 0.0 ), speed ( example 2.0 ) );
        return 1;
    }
    if ( !strcmp( cmdtext, "/close", true ) )
   {
        F_MoveObject ( gate, coordinates where the gate moves ( example 0.0, 0.0, 0.0 ), speed ( example 2.0 ) );
        return 1;
   }
    return 0;
}