uniq

Overview

uniq reports or filters adjacent duplicate lines. Almost always used after sort unless input is already grouped.

Syntax

uniq [options] [input [output]]

Common Options

Option	Description
-c	Count occurrences
-d	Only duplicates
-u	Only unique lines
-i	Ignore case
-f N	Skip first N fields
-s N	Skip first N chars
-w N	Compare width
-z	NUL-terminated

Examples with Explanations

sort file.txt | uniq
sort file.txt | uniq -c | sort -nr
sort file.txt | uniq -d
sort file.txt | uniq -u
cut -d: -f1 /etc/passwd | sort | uniq -c

From logs

awk '{print $1}' access.log | sort | uniq -c | sort -nr | head

Related Commands

• sort -u — unique sorted
  
• comm — compare sets
  
• awk '!a[$0]++' — unique without sort (memory)