You should mention this behavior of uniq (from the man page on my machine): Note: ’uniq’ does not detect repeated lines unless they are adjacent. You may wan

You should mention this behavior of uniq (from the man page on my machine): Note: ’uniq’ does not detect repeated lines unless they are adjacent. You may want to sort the input first, or use ‘sort -u’ without ‘uniq’. Your movies.csv file is already sorted, but you don't mention that sorting is important for using uniq, which may be misleading. $ cat tmp.txt AAAA AAAA BBBB DDDD BBBB $ uniq -d tmp.txt AAAA