执行uniq命令前，需要先用sort命令做排序，否则很有可能uniq会失效，因为uniq只会对相邻的内容做合并。
Linux manual
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’. Also, comparisons honor the rules specified by ‘LC_COLLATE’.