Updated: May 6, 2022
Comparing files, not a difficult task, easy peasy. Comparing files visually, not so much. Now and then, almost everyone will have a need to look at two versions of the same document and try to find the subtle differences between them. Sometimes, the application you're working with will have a built-in comparison feature, which makes things simpler. Sometimes, you will have to figure it out on your own, or use a dedicated program.
In Linux, there is a wealth of file comparison tools and utilities available, most of them built on top of the command-line diff program. They all follow the same basic principle of showing you two versions of the same file, side by side, and highlighting the changes and differences (hence the name). But one program stands out in this domain, and it's meld. To wit, we shall review.
Spot the differences
Meld is a GUI program, designed for two-way AND three-way file comparisons. It can compare text files side by side, but also recurse through entire directories and show you the full range of relevant differences there. The program also works with version control tools, so you can compare code commits, file edits, and alike. You can install meld in most Linux distributions from their relevant repos without any great fussing.
Once you launch it, the main interface allows you to perform (one of its) three core functions. If anything, this is the most confusing part of the program. Click on File comparison, and it will pop open two file selection fields just underneath (and optionally, the third one, too). But the fields are aligned to the main menu categories above, so it may give you a wrong impression that you're selecting something related to Directory comparison or Version control view. But once you get past this wee hurdle, you're golden.
Simple, intuitive, elegant
Meld turns the file comparison task into a pleasant one. You can clearly see where the differences lie. Optionally, you can use syntax highlighting (for supported file formats, of which there be many), as well as word wrapping. You can then manually move changes left and right, with each little arrow showing you where and how the blocks of text would flow.
Meld also has a tabbed interface (for any pair or trio of compared files, or the other two types of comparisons), so you can have it all shown in one window, nice and tidy. The GUI lets you advance change by change, push/pull changes in both directions, and you can even set synchronization points, which means you can work on changes only within a part of your files and not the entire contents. The document panes are fully writable, so you can simply insert the mouse cursor, and then type. Then, Meld also lets you format your changes as patch files. Very neat.
Not only is Meld practical and powerful, you also have a fair deal of flexibility in how you do things. You can choose the display font, enable text wrapping, highlight syntax, add line numbers, and then some. For folder comparisons, you can decide what method to use, including NTFS-compatible timestamp resolution. With version control, you can set the order on how you manage changes and commits. Lastly, file and text filters allow you to ignore certain types of objects (like temporary files or lock files inside folders), so that your comparisons don't stumble on unimportant bits. It's all there.
There you go. Software-related enthusiasm be a rare emotion in me soul these days, but now and then, a nugget of gold erupts from the mire, and you're left with a grin on your weary face. Meld seems to be the program that has just the right dose of everything. It's neither under-engineered nor over-engineered, and it has no bloat. The only downside is the four seconds of confusion you suffer on first usage, and after that, it be smooth sailing.
If you're in need of a program to reliably and clearly help you track changes and diffs in your files and projects, and you want to do it in an elegant way, look no further than Meld. It has everything to support you in your mission, with an understated UI that delivers a solid punch. I think we're done here.