Duplicate Line Remover
Remove duplicate lines from text. Options for case-sensitive matching, trimming whitespace, preserving order, and showing removed line counts.
How to Use Duplicate Line Remover
- 1Paste or type your text with duplicate lines.
- 2Choose case sensitivity and whitespace trimming options.
- 3View the deduplicated output with removed line count.
- 4Copy the unique lines or download as a text file.
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Frequently Asked Questions
What counts as a duplicate line?▾
By default, two lines are duplicates if they are identical character-by-character (case-sensitive). With case-insensitive mode on, "Apple" and "apple" are duplicates. With whitespace trimming on, " hello " and "hello" are duplicates. The first occurrence of each unique line is kept; all subsequent occurrences are removed. Empty lines can also be optionally removed.
How do I remove duplicate lines on Linux or Mac?▾
Using Unix tools: "sort -u file.txt" sorts and removes duplicates. "awk '!seen[$0]++'" removes duplicates while preserving original order. "uniq file.txt" removes consecutive duplicates (requires pre-sorting). For case-insensitive: "awk '!seen[tolower($0)]++'". In Python: "lines = open('f.txt').readlines(); unique = list(dict.fromkeys(lines))".
When should I preserve insertion order vs. sort?▾
Preserve order when line position matters: log entries, SQL results, configuration files, data with implicit ordering. Sort when order does not matter and you want alphabetical output: word lists, tag lists, CSV column values, import statements. This tool preserves insertion order by default (first occurrence wins), with an option to sort the output afterward.
What is the difference between unique and distinct?▾
In everyday use, "unique" and "distinct" are synonymous in this context. In database terminology: DISTINCT removes duplicate rows from query results; UNIQUE is a constraint that prevents duplicates from being inserted. Both mean "keep only one occurrence of each value". SQL: SELECT DISTINCT column FROM table returns each value once, regardless of how many times it appears.
Can this handle very large files?▾
This browser-based tool handles text pasted into the input field. For very large files (millions of lines), use command-line tools instead: awk '!seen[$0]++' input.txt > output.txt. The browser tool is practical for up to ~50,000 lines. For programmatic deduplication in code, Python sets or JavaScript Set objects are the most efficient approach.