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lang-c
tac {input} | uniq -w 9work?-w Nwill only consider the firstNchars. For my local file I had a 9 char ID in the first column, souniq -w 9.uniq -w 5should work. I think your and Mikels answers are better, since they do not make an assumption about the number of chars in the first column. However, if the input follows such a constraint, thenuniq -wis the fastest.