Notepad++ remains one of the most accessible solutions for Windows users tackling duplicate text. Install the Compare plugin through the Plugin Admin menu, then open both documents in separate tabs. Navigate to Plugins > Compare > Compare to view differences side-by-side with color-coded highlighting.

To remove duplicates, use the TextFX plugin (or the built-in Edit menu in newer versions): select all text, then choose Edit > Line Operations > Remove Duplicate Lines. This method preserves your original line order and handles files with thousands of entries efficiently.

Visual Studio Code offers similar functionality through extensions like Duplicate Remover or Compare Folders. Open both files in split view, install your preferred extension from the Extensions marketplace, then run the duplicate removal command from the Command Palette (Ctrl+Shift+P or Cmd+Shift+P). VS Code's advantage lies in its cross-platform availability and powerful regex support for complex matching scenarios.

For Mac users, BBEdit provides native duplicate removal through Text > Process Duplicate Lines. Open your combined document or paste both files' contents into a single window, select the text, and choose whether to delete duplicates or extract unique lines to a new document. BBEdit also lets you specify case-sensitive matching and sort lines before processing.

PowerShell on Windows handles duplicate removal with a single command pipeline. Combine both files using Get-Content file1.txt, file2.txt, pipe to Sort-Object -Unique, then output to a new file with > output.txt. The complete command looks like: Get-Content file1.txt, file2.txt | Sort-Object -Unique > cleaned.txt. This approach automatically sorts your results alphabetically, which may or may not match your needs.

Linux and Mac users can leverage the classic sort and uniq utilities. Concatenate files with cat file1.txt file2.txt, pipe through sort to arrange lines alphabetically, then pipe to uniq to remove consecutive duplicates: cat file1.txt file2.txt | sort | uniq > output.txt.

Add the -i flag to sort for case-insensitive comparison, or -u to combine sorting and duplicate removal in one step: cat file1.txt file2.txt | sort -u > output.txt.

The awk command offers more control for advanced scenarios. To preserve original order while removing duplicates, use: awk '!seen[$0]++' file1.txt file2.txt > output.txt. This keeps the first occurrence of each line and discards subsequent matches without sorting.

Handle case sensitivity intentionally based on your data. "Apple" and "apple" are different lines by default in most tools, but identical if you enable case-insensitive matching. Decide which behavior matches your goal—keeping variant capitalizations might matter for proper nouns, while standardizing case works better for general text cleanup.

Whitespace differences create hidden duplicates. A line with trailing spaces or tabs won't match an otherwise identical line without them. Trim whitespace first using your editor's find-and-replace function (search for \s+$ in regex mode and replace with nothing) or add preprocessing commands like sed 's/[[:space:]]*$//' in your command pipeline.

Consider whether you need to preserve line order. Sorted output works fine for lists and datasets, but destroys meaningful sequence in logs, narratives, or time-series data. Choose tools like awk or Notepad++'s Remove Duplicate Lines feature when order matters, and sorting-based methods when alphabetical arrangement helps.

Test your process on a small sample before running it on production data. Make backup copies of original files, verify that your chosen tool handles special characters correctly, and confirm the output matches expectations. A five-minute test run prevents hours of recovery work if something goes wrong with large datasets.