<(command)
is a bashism called Process substitution
You have to run your script with bash, eg do bash script.bash
Or if you want to use sh, you could write the results to a file, like this :
grep eth0 /proc/net/dev > file1
sleep 1 ; grep eth0 /proc/net/dev > file2
diff file1 file2
7
solved sh: 1: Syntax error: “(” unexpected error