The GNU diff and patch utilities let you compare files to generate a patch that describes the changes between files. You can then apply the patch file on that machine or another. You might think to use diff and patch on XML files, since they are just text files -- and depending on your application, diff and patch might serve your needs well.

The Linux command diff can be used to create a script that will list the differences between two directories. This comparison is often very useful when writing scripts.

With diff-ext, GNOME users can compare and merge files from within Nautilus. If, instead, you use KDE 3, try out kdiff-ext from the same site, which works with Konqueror. Each utility handles paths to files and directories and invokes an external diff tool to perform the grunt work.

colordiff is a wrapper for diff and produces the same output as diff but with coloured syntax highlighting at the command line to improve readability. The output is similar to how a diff-generated patch might appear in Vim or Emacs with the appropriate syntax highlighting options enabled.

"One nice feature of Emacs, that is as old as Emacs itself, are buffers. Most Emacs users like them because you can have multiple buffers open at once and work on many things at once. And for the record, I'm actually a big fan of the Emacs buffer menu..."

In diff tool speak, a visual diff tool is a GUI application. Meld is such a tool: a tool for displaying differences between files (and directories) and also for merging the differences. Meld is programmed in Python.

"I've been reading lots of blogs and opinions about emacs the last few days. What strikes me is all of these people who brag about how large their .emacs files have become. So let me make this very clear: If your .emacs file is longer than a page YOU ARE DOING IT WRONG. Why?

Certain situations require you to quickly confirm which files between two directories are different, and while your particular requirements may suggest writing a script for this task, I want to make sure you're familiar with the basics first - majority of directory comparisons can be done using diff command (yes, that's right - the same one used for comparing files).

"This tutorial shows you how to obtain help from Emacs in various ways. After working through this tutorial, you'll know how to get descriptions of keystrokes, commands, functions, and read and browse through the many documentation resources that come with this world-famous open source editor. [...]