In the case of gzip -9 < /dev/random | dd of=/tmp/gibberish the shell's not actually doing anything but forking things and connecting file descriptors of pr

In the case of gzip -9 < /dev/random | dd of=/tmp/gibberish the shell's not actually doing anything but forking things and connecting file descriptors of processes to each other gzip -9 < /dev/random | while read line ; do echo "$line" ; done > /tmp/gibberish The stdout of gzip is being processed by shell, and will make all the nulls go away. (edited to add another example:) Similarly - it isn't printing that you can't do -- it's anything -- consider: case $(cat /bin/sh) in $(cat /bin/bash)) echo "they're the same!" ;; *) echo "they're not the same!" ;; esac This is obviously an insane way to see if two files are identical, but worse -- it's going to fail for two different files whose only difference is how many nulls are in the file.