Compare files and return only the differences using Notepad++ - compare

Question

Notepad++ has a Compare Plugin tool for comparing text files, which operates like this:
Launch Notepad++ and open the two files you wish to run a comparison
check on.
Click the “Plugins” menu,
Select “Compare” and click “Compare.”
The plugin will run a comparison check and display the two files side
by side, with any differences in the text highlighted.
This is a nice feature, and which I have used happily for some time. Now, I have been looking for an option to go further and select the highlighted differing lines (e.g. by deleting the non-highlighted ones), or vice versa: i.e. expunge the highlighted lines.
Is there a straightforward way to achieve this?

Answer 1

To substract two files in notepad++ (file1 - file2) you may follow this procedure:
Recommended: If possible, remove duplicates on both files, specially if the files are big. To do this: Edit => Line operations => Sort Lines Lexicographically Ascending (do it on both files)
Add ---------------------------- as a footer on file1 (add at least 10 dashes). This is the marker line that separates file1 content from file2.
Then copy the contents of file2 to the end of file1 (after the marker)
Control + H
Search: (?m-s)^(?:-{10,}+\R[\s\S]*+|(.*+)\R(?=(?:(?!^-{10,}$)-++|[^-]*+)*+^-{10,}+\R(?:^.*+\R)*?\1(?:\R|\z))) note: use case sensitivity according to your needs
Replace by: (leave empty)
Select Regular expression radio button
Replace All
You can modify the marker if It is possible that file1/file2 can have lines equal to the marker. In that case you will have to adapt the regular expression.
By the way, you could even record a macro to do all steps (add the marker, switch to file2, copy content to file1, apply the regex with a single button press.
Edited:
Changed the regex to add some improvements:
Speed related:
Avoid as much backtracking as possible
Avoid searching after the mark
Usability:
Dashes are allowed for the lines. But the separator is still ^-{10,}$
Works with other characters besides words
Speed comparison:
New method vs Old method
So basically 78ms vs 1.6seconds. So a nice improvement! That makes comparing Kilobyte-sized files possible.
Still you may want to use some dedicated program for comparing or substracting bigger files.

Answer 2

If the number of differences is not large, a quicker method might be just bookmarking each differing line using keyboard shortcuts. Starting from the beginning of the file, press Alt+Page Down to focus on the first difference, and then press Ctrl+F2 to bookmark it. Continue with alternatingly pressing Alt+Page Down and Ctrl+F2 until the last difference.
With all the differing lines bookmarked, you can use any of the operations under "Search -> Bookmarks" menu:
Cut Bookmarked Lines
Copy Bookmarked Lines
Paste to (Replace) Bookmarked Lines
Remove Bookmarked Lines
Remove Unmarked Lines

Answer 3

I have a dirty workaround for this. It saves some time compared to Control+C, Alt+Tab, Control+V; Control+C, Alt+Tab, Control+V; ... but It may not be worth on big files or if the differences for both files are big. For bigger files you may prefer using some other tool.
Typically this works best when comparing group of 'words' and does not work with content that is tabulated (like source code)
So the workaround is:
Optional: (depends on the content that's being compared) Sort both files (it will make the future comparison easier) To do this: Edit => Line operations => Sort Lines Lexicographically Ascending (do it on both files)
Compare files with the plugin
Choose one file and inspect the lines you want to keep. Add one tabulator before each of those lines. Remeber you can select several lines and press tab for tabulating them. Optionally, you may add tabulators to the lines you want to remove
Sort the file. The tabulated lines will come up first. So now you can copy-paste them (or copy-paste the untabulated ones)

Answer 4

move the files to a linux box and then execute diff command:
$ diff file1.txt file2.txt > file_diff.txt