Bash：常用命令工具-uniq

NAME

       uniq - report or omit repeated lines



SYNOPSIS

       uniq [OPTION]... [INPUT [OUTPUT]]



DESCRIPTION

       Filter adjacent matching lines from INPUT (or standard input), writing to OUTPUT (or standard output).



       With no options, matching lines are merged to the first occurrence.



       Mandatory arguments to long options are mandatory for short options too.



       -c, --count

              prefix lines by the number of occurrences



       -d, --repeated

              only print duplicate lines



       -D, --all-repeated[=delimit-method]

              print all duplicate lines delimit-method={none(default),prepend,separate} Delimiting is done with blank lines



       -f, --skip-fields=N

              avoid comparing the first N fields



       -i, --ignore-case

              ignore differences in case when comparing



       -s, --skip-chars=N

              avoid comparing the first N characters



       -u, --unique

              only print unique lines



       -z, --zero-terminated

              end lines with 0 byte, not newline



       -w, --check-chars=N

              compare no more than N characters in lines



       --help display this help and exit



       --version

              output version information and exit



       A field is a run of blanks (usually spaces and/or TABs), then non-blank characters.  Fields are skipped before chars.



       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_COL‐

       LATE'.

以上是man输出。

从最后的note中可以知道当使用uniq进行去重，要求输入重复项是相邻的。这个比较好理解，要求重复项时连续的话可以省去一个hashmap的空间来做统计。为了获得这样的一个输入，可以先对数据进行一个排序操作，这样重复项必然是连续相邻的。

有如下文本文件：

the

day

is

sunny

the

the

sunny

day

is

today

is

sunny

day

UASE CASE 1.

首先对单词内容做一个去重处理（先排序，再去重）

$ sort words.txt | uniq

day

is

sunny

the

today

USE CASE 2.

重复统计：

$ sort words.txt | uniq -c

      3 day

      3 is

      3 sunny

      3 the

      1 today

USE CASE 3.

只输出重复项或者只输出唯一项：

$ sort words.txt | uniq -d

day

is

sunny

the

$ sort words.txt | uniq -u

today