'xp_cmdshell returning null and not logging

So im trying to log a test message to a directory in sql but eveytime i run the query i get output:null and no logging whatsoever. Any help

Begin --To append
    SET @strCmdLogFailed= 'echo >> '+ @strErrorLogPath + 'My Item           Something           Date' --+ Convert(Varchar(5000), @strItemsNotRegisteredList)
    select @strCmdLogFailed
    Exec master..xp_cmdshell @strCmdLogFailed
End


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