How to Remove Duplicate Lines from Text
Line Deduplication
When to Dedupe Lines
Remove repeated lines from log exports, email lists, CSV columns, API ID dumps, or any pasted text where only unique lines matter. The first occurrence of each line is kept.
Real-World Examples
Deduplicate error messages from a log file before analysis
Clean a list of URLs where the same link was pasted multiple times
Reduce a column of IDs exported from a spreadsheet
Common Mistakes
- Trailing spaces making visually identical lines distinct
- Expecting case-insensitive deduplication — comparison is exact by default
- Deduplicating before sorting when you need alphabetical unique output — sort lines afterward
Developer Tips
- Run Whitespace Tools first to trim lines if spacing varies
- Combine with Sort Lines for ordered unique lists
- CLI equivalent:
sort file | uniq
Frequently asked questions
Which duplicate is kept?
The first occurrence of each line is preserved. Later duplicates are removed.
Are blank lines considered duplicates?
Yes. Multiple empty lines collapse to one empty line.
Is comparison case-sensitive?
Yes. "Error" and "error" are treated as different lines.