Your backslash was not at the right place...And you need a space before...
Addendum...
Thinking of it you are going to be in trouble for your are reading /proc and /sys anyway before the grep and I cant see the system say nothing...
In other words wrong logic, think again!
Ok, thank you. However your solution does NOT work.
The final list contains lots of files beginning with /sys/
So I think the grep filtering does not work this way.
Maybe the grep is wrong.
Any other suggestion?