Maybe is relying on the linux caching the file in memory? Then if you read it again is already in memory. If so I don't think it is particularly useful, given

Maybe is relying on the linux caching the file in memory? Then if you read it again is already in memory. If so I don't think it is particularly useful, given that using the file anyway already puts it into the cache for later use And yes, /dev/null is a abyss and everything written in it is discarded