uniq

Additional Notes

uniq removes or reports adjacent duplicate lines. It only compares neighboring lines, so input is usually sorted first.

Use sort | uniq to find unique lines across a whole file or stream.

Syntax

uniq [options] [input [output]]

Parameters

• options: Flags that change how uniq behaves.
• file: Text file to read or process.

Common Options

• -c, --count: Prefix lines with occurrence counts.
• -d, --repeated: Print only duplicate lines.
• -u, --unique: Print only lines that are not duplicated.
• -i, --ignore-case: Ignore case differences.
• -f N: Skip first N fields.
• -s N: Skip first N characters.

Examples

sort names.txt | uniq

Print unique names.

sort access.log | uniq -c

Count repeated lines.

sort errors.txt | uniq -d

Show only lines that appear more than once.

sort words.txt | uniq -u

Show only lines that appear once.

sort names.txt | uniq -ci

Count duplicates while ignoring case.

Practical Notes

• uniq checks adjacent lines only.
• Use sort first unless you intentionally care about neighboring duplicates.
• sort | uniq -c | sort -nr is useful for frequency counts.
• For field-aware processing, consider awk.