uniq Command - Report or Omit Repeated Lines

The uniq command is used to filter out or report repeated lines in a file or from standard input. It is commonly used to process sorted files to remove or count duplicate lines.

Syntax

uniq [options] [input_file [output_file]]

Examples

sort file.txt | uniq

uniq -c file.txt

uniq -d file.txt

Notes

• Input must be sorted for uniq to detect duplicates correctly.
• Commonly used with sort for deduplication tasks.
• Can also output only unique or only duplicate lines with options.