A colleague of mine noticed some odd behaviour with the sort command today, and I was wondering if anyone knows if the output of this command is intentional or not?
Given the file:
ABC_22 ABC_43 ABC_1 ABC_1 ABC_43 ABC_10 ABC_123
We are looking to sort the file with numeric sort, and also make it unique, so we run:
sort file.txt -nu
The output is:
ABC_22
Now, we know that the numeric sort won’t work in this case as the lines don’t begin with numbers (and that’s fine, this is just part of a larger script), but I would have expected something more along the lines of:
ABC_1 ABC_10 ABC_123 ABC_22 ABC_43
Does anyone know why this isn’t the case? The sort acts as one would expect if given just the -u or -n options individually.
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Answer
You are missing specifying the de-limit on the second field of GNU sort as
sort -nu -t'_' -k2 file ABC_1 ABC_10 ABC_22 ABC_43 ABC_123
The flag -n for numerical sort, -u for unique lines and the key part is to set de-limiter as _ and sort on the second field after _ done by -k2.