Problem with Bash output redirection

Question

I was trying to remove all the lines of a file except the last line but the following command did not work, although file.txt is not empty.

$cat file.txt |ta         


        

Answer 1

As Lewis Baumstark says, it doesn't like it that you're writing to the same filename.

This is because the shell opens up "file.txt" and truncates it to do the redirection before "cat file.txt" is run. So, you have to

tail -1 file.txt > file2.txt; mv file2.txt file.txt