shell怎么判断两个文件内容是否相同

#cat diff_two_file
#/bin/sbin
file1=/mnt/mmc/test/aa
file2=/mnt/mmc/test/bb
diff $file1 $file2 > /dev/null
if [ $0 == 0 ]; then
echo "Both file are same"
else
echo "Both file are different"
fi
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$0 是上一执行命令的返回值。
diff 命令返回值为 0，说明两个文件相同， 否则两个文件不相同。