> #># 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?
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Pika Supports Ukraine
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hyunjung
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Possible duplicate of [How can I use a file in a command and redirect output to the same file without truncating it?](https://stackoverflow.com/q/6696842/608639), [input and output redirection to the same file](https://stackoverflow.com/q/29899654/608639), etc. – jww Apr 12 '19 at 01:54
1 Answers
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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.
Maxime
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Why the command "test > test " means that declaration gives an empty test file? ****^^** – hyunjung Apr 12 '19 at 01:47
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okayyy thank you !! and i have another question : why "test > test " is faster executing than "cat < test"? – hyunjung Apr 12 '19 at 01:54