There is the "Compare" plugin. You can install it via Plugins -> Plugins Admin... (or Plugins -> Plugins Manager in older versions of Notepad++) in the top menu.
Alternatively you can install a specialized file compare software like WinMerge.
Answer from Lars Fischer on Stack OverflowThere is the "Compare" plugin. You can install it via Plugins -> Plugins Admin... (or Plugins -> Plugins Manager in older versions of Notepad++) in the top menu.
Alternatively you can install a specialized file compare software like WinMerge.
Update:
- for Notepad++ 7.5 and above use Compare v2.0.0
- for Notepad++ 7.7 and above use Compare v2.0.0 for Notepad++ 7.7, if you need to install manually follow the description below, otherwise use "Plugin Admin".
I use Compare plugin 2 for notepad++ 7.5 and newer versions. Notepad++ 7.5 and newer versions do not have plugin manager. You have to download and install plugins manually. And YES it matters if you use 64bit or 32bit (86x).
So Keep in mind, if you use a 64-bit version of Notepad++, you should also use a 64-bit version of the plugin, and the same is valid for 32-bit.
I wrote a guideline how to install it:
- Start your Notepad++ in administrator mode.
- Press F1 to find out if your Notepad++ is 64bit or 32bit (86x), hence you need to download the correct plugin version. Download Compare-plugin 2.
- Unzip Compare-plugin in a temporary folder.
- Import the plugin from the temporary folder.
- The plugin should appear under the Plugins menu.
Note:
It is also possible to drag and drop the plugin.dllfile directly in the plugin folder.
64bit:%programfiles%\Notepad++\plugins
32bit:%programfiles(x86)%\Notepad++\plugins
Update Thanks to @TylerH for this update: Notepad++ Now has "Plugin Admin" as a replacement for the old Plugin Manager. But this method (answer) is still valid for adding plugins manually for almost any Notepad++ plugins.
Disclaimer: the link to this guideline refer to my personal website.
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Basically I'm just doing simple checks to see the difference between two files, specifically in my case I'm using arkenfox user.js for firefox. I like to compare the update to the old version to see what changed and see if I need to make any updates to my user-overrides.js
The color coding also helps immensely. And seeing the files side by side with the changes highlighted, while being able to edit them if needed, helps too. (I've also used it to see changes I've made in user-overrides.js).
Edit: I'm very new to linux and because everything is new I don't have that sense of what to try first, like I do with windows. With mac or android I have a better sense as well, at least have an idea with those of what to search for or a place to start. With linux it's so unfamiliar and new to me, just kinda very overwhelming and too many things to process at once. I just kinda blank out for a while before I come up with an idea.
I figured it out though, I installed Kompare to use with Kate and that seems to be working well. It was a little confusing and counter intuitive process to what I'm used to. I was thinking maybe I need to install plugins, rather than pull programs from the software manager, and I don't always know what to look for! I wasn't certain it would work since it's for KDE and I'm on Cinnamon (keep forgetting about the DE, I'm used to just one desktop environment), I've only quickly checked a file, not done much with it yet and it worked for what I needed.
Would the plugin "Compare" of Notepad++ would do the trick?
You can install it from the menu of Notepad++ plugins=> Plugin Manager=> Compare 1.5.6
Here's the official description: A very useful diff plugin to show the difference between 2 files (side by side). Author: Ty Landercasper, now maintained and updated by Jean-Sebastien Leroy Source: http://sourceforge.net/projects/npp-plugins/files/ComparePlugin/Compare_1_5_5_src.zip/download
An old question, but...
- Compare the files in WinMerge
- Tools -> Generate Patch (save this)
The patch has changes from both, but also extra markup. In notepad++, do the following replaces:
Search Mode: Regular Expression Find What: ^[0-9-].*$ Replace With: <blank> Replace All.
Search Mode: Regular Expression Find What: (<|>) Replace With: <blank> Replace All- Use the TextFX plugin in notepad++ either do a Tools->case-insensitive sort (output UNIQUE option selected), or Edit->Delete blank lines
Bit mungy, but I've yet to find a tool that will do this in one click.
In Notepad++ 5.7 you can right-click on a tab and select "Move to Other View". You can also select "Clone to Other View" if you want to have the same file open more than once and see different parts of it. You can right-click the divider line and rotate the views to be either side-by-side or top-and-bottom.

As mentioned in the comments, there's a very handy compare plugin for Notepad++, that allows side-by-side comparison, indicating discrepancies.

(Click image to enlarge)
You could use a tool such as Textpad that allows you to sort the files as well as compare them - as long as the tool, (and you), doesn't save the file after the sort you should be OK.
The latest version of Notepad++ (v6.7.8.2) contains a 'order by' function.
This will be sufficient for your needs, so long as the header row isn't going to cause trouble in the ordering.
Note that the compare plugin has been removed though, so you'll need to download it from here.