I want to maximize my sd card lifespan and Im wondering if redirecting output to /dev/null will reduce my sd card life.
Sending output to
/dev/null means "throw it away". It has no impact on your SD card at all. Of course, the commands that you're running prior and piping to
/dev/null may well be affecting your SD card.
Anything you redirect to
/dev/null gets dumped out an airlock. For example if you were to
cat /boot/kernel.img > /dev/null what's happened is effectively nothing. Of course,
cat /boot/kernel.img would normally just write to the terminal, which is also only a short-term memory cache on the screen. That never gets written to the SD either. There are generally only very specific instances you might want to write to
/dev/null for actual benefit. For example, doing first pass video encoding still prodcues an output file. This you can send to
/dev/null to save writes on the card. When you do the second pass of the encoding then you do the actual writing.