uniq

The uniq command filters out adjacent, repeated lines in a file. It is often used in combination with the sort command since uniq only detects duplicates that are next to each other.

Basic Syntax

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

Common Options

Option	Description
-c, --count	Prefix lines by the number of occurrences.
-d, --repeated	Only print duplicate lines, one for each group.
-u, --unique	Only print unique lines (lines that do not have duplicates).
-i, --ignore-case	Ignore differences in case when comparing.
-f, --skip-fields=N	Avoid comparing the first N fields.

Real-world Examples

1. Remove adjacent duplicate lines:

   uniq items.txt

2. Count occurrences of each line:

   sort items.txt | uniq -c

3. Show only duplicate lines:

   sort items.txt | uniq -d

4. Show only unique lines:

   sort items.txt | uniq -u