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DarckBlezzer avatar Server

Why tail to same file create a empty file, or empty the file?

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DarckBlezzer

I try to maintain the last lines of a file, but when tail -n 10 test.txt > test.txt create or empty the file...

SO: Ubuntu server

Example:

#test.txt file 20 May 23 12:24 test.txt
 a
 a
 a
 a
 a
 a
 a
 a
 a
 a

use tail -n 10 test.txt > test.txt
new file is empty 0 May 23 12:36 test.txt

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Rob
Does this answer your question? [Linux: How to use a file as input and output at the same time?](https://serverfault.com/questions/135507/linux-how-to-use-a-file-as-input-and-output-at-the-same-time)
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Rob

Output Redirection by the shell (as well as input redirection) happens before the requested command is started. The > file output redirect opens filefor writing and creates file if it does not exist; if it does exist it is truncated to zero size.

Once that has happened and your tail command is started it can only read an empty file...

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