FAQ: Redirection - uniq

This community-built FAQ covers the “uniq” exercise from the lesson “Redirection”.

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This exercise can be found in the following Codecademy content:

Web Development

Learn the Command Line

FAQs on the exercise uniq

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Hello, how to replace the content of an existing file with duplicates by the content without duplicates?

For example: uniq file.txt > file.txt doesn’t work, the resulting file will be empty.

For the sort program, a solution is provided in https://stackoverflow.com/questions/29244351/how-to-sort-a-file-in-place_ : use sort -o file.txt file.txt

A common mistake is to try to redirect the output to the same input file (e.g. sort file > file). _ This does not work as the shell is making the redirections (not the sort program) and the input file (as being the output also) will be erased just before giving the sort program the opportunity of reading it.

For the the uniq program, I can’t identify a solution. Any clue?

Hi Script,

Rewording this, you’d like to delete duplicates in a file without creating a new one?
You can first do the uniq and sort to the new file name, then delete the contents of the original file, then direct the new file name’s contents back to the original.
I’m not sure if there’s a better way but it worked!
here is the link that gave me the idea, aside from our earlier lessons on replacing contents.

see snapshot
sort then delete then replace

actually @script2133254651 the echo command isn’t necessary because > replaces contents.
i suppose the only other option is sorting in place. Would be great if a moderator could advise?


Are you looking for sort file.txt & uniq file.txt?