Output redirection to samefile

[ric_Poirier]

Hi,

I am currently studying the ">" and ">>" tools for output redirection. I have a file, eleves.txt, in which some lines a repeated. My goal is to sort them out. For this, I want to use the sort command. In a terminal, I have written:

sort eleves.txt > eleves.txt

Now I know that, using the ">" tool for output redirection, if the file already exists, it will be overwritten. My problem is that when I type

cat eleves.txt

in the terminal (after having sorted the file a redirected the output to the same file), all data from eleves.txt seems to have disapeared. I was expecting the files to have all its lines sorted instead. Please help me understand this behaviour...

[Impavidus]

>> will append the sorted file, so sort eleves.txt >>eleves.txt leads to a sorted list of (pupils?).
> will truncate the file to zero and then write the output. It appears that the shell first truncates the file to make it ready for writing and only then starts the sort command, which therefore encounters an empty file, which after sorting still is an empty file. You could try first storing it as a temporary file under a different name.

If you want to delete repeated lines, have a look at the uniq command. See man uniq.

sort input | uniq >output

[ric_Poirier]

Okay, thanks for the reply!