Hi there, recently I had to debug weird problem. Finally I figured it out.
Virtual file systems like /sys or /proc usually don't care about file sizes. All files have a size of 0. This leads to difficulties as diff sometimes looks for file sizes. Say you do: > $ cp /proc/cmdline my_cmdline > $ diff /proc/cmdline my_cmdline ; echo $? > 0 // ok, files don't differ > $ diff --brief /proc/cmdline my_cmdline > Files /proc/cmdline and mycmdline differ The --brief option triggers a binary compare, as we aren't interested in the actual differences this makes sense. As a first step, file sizes are compared (0 vs ~150) and the files are reported as different. I am not sure how to fix this. I.e. are the files different or not? What is the correct behavior. In any case --brief should have no influence on the overall result! I see the following options (I prefer the 2nd): 1: Don't use file sizes in comparing. This is rather expensive but would certainly fix it. 2: add a --use-file-sizes flag which enables decisions based on file sizes. Without this flag, always look into the files. And --brief should report, if the files differ because of their data or size. That is > $ diff /proc/cmdline my_cmdline ; echo $? > 0 // ok, files don't differ > $ diff --brief /proc/cmdline my_cmdline ; echo $0 > 0 > $ diff --brief --use-file-sizes /proc/cmdline my_cmdline > Files /proc/cmdline and mycmdline differ in file size 3: Leave it at it is and add a warning in the man page. However that would be very inconvenient. best, stephan
