Ignore the first line

Question

I am using the following command to organize a file:

sort -u arquivo.csv -o arquivo.csv

But I need to ignore his first line, in case the header.

How can I do that?

Answer 1

You can use the utility tail to skip the first line of the input file before redirecting its output to sort, look at you:

$ tail -n +2 arquivo.csv | sort -u -o arquivo.csv

According to the utility documentation sort, the sorting process is done in memory, before opening/writing the output file (specified with the option -o), this guarantees an ordination in place of the file securely.

Note that the first line of the file is destroyed with the execution of that command.

Reference: https://unix.stackexchange.com/questions/29697/does-sort-support-sorting-a-file-in-place-like-sed-in-place

Answer 2

Use the command tail with the option -n:

tail -n +2 arquivo.csv

In the case, -n +2 will display only from the second line onwards (you can change the number to any value you need).
The sign of + is also important, because if you write only -n 2, it will show the last two lines.

Then you can pass the result directly to the sort:

tail -n +2 arquivo.csv | sort -u > arquivo_ordenado.csv

Also, I recommend saving the output in another file (as I did above), since reading and writing in the same file doesn’t usually work very well (by own experience, depending on the command, the file is overwritten and/or truncated and you end up losing the data - I don’t know how the sort treat it, but I’d rather not risk).

^{To answer from Lacobus answers this specific question about the sort.}

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Keep the header

As well remembered in the comments, with the above command, the first line (header) is lost. If you need it in the final file, one way to do it is to break in two commands.

First save the first line in the final file, with the command head:

head -1 arquivo.csv > arquivo_ordenado.csv

The parameter -1 says to pick up only the first line. Then do the tail and sort, and add the result to the file:

tail -n +2 arquivo.csv | sort -u >> arquivo_ordenado.csv

Notice I’m wearing it now >>, which adds the information at the end of the file. If I use only >, the contents of the file is overwritten and the header will be lost.