What happens when you grep the file you've redirected grep to?
Reminds me of how easy it is to destroy a file with sed:  sed 's/a/b/' test.txt > test.txt

After that command the file is empty no matter what was in there before. Instead you have to use the -i flag like:  sed 's/a/b/' -i test.txt

And different operating systems seem to behave differently:https://stackoverflow.com/questions/5171901/sed-command-find...