带有重定向的 Cat 命令导致一个空的测试文件

Question

> #># cat /etc/group > test
> #># cat < test > test
> #># cat test

I inputted the second command in prompt and checked the test file. I found that test_file was empty.

Why does it happen?

Answer 1

My guess is that you are redirecting test > test first but the result of this declaration gives an empty test file. And then you redirect this empty test file with cat < test which displays this empty file.

That's why your second and third command print nothing.