How to Remove Duplicate Lines in Linux (uniq)

uniq filters out adjacent duplicate lines from sorted input, leaving only unique lines.

Key points

• uniq only removes duplicates that are directly adjacent — sort the input first for it to work reliably: sort file.txt | uniq
• uniq -c prefixes each line with a count of how many times it occurred consecutively
• uniq -d shows only the lines that had duplicates, which is useful for finding repeated values

Example

sort names.txt | uniq -c