Ever have a file and wonder what changed? You need a diff tool!
In computing, diff is a file comparison utility that outputs the differences between two files. The program displays the changes made per line for text files.
There are diff tools available for almost any platform you can think of ranging from simple command line utilities to complex GUI based applications.
Here is a screenshot using Beyond Compare comparing my current project build file to the original one when I started the project. Red means changes occurred! :)
If you use Eclipse there is a diff tool built in! Right click any file and select "Compare With". You can compare files in your local history, and if you are using source control, you can compare with previous revisions. (In the screenshot below I have a BeyondCVS plugin installed which allows me to use Beyond Compare within Eclipse).
Many tools will also let you compare not only files but directories as well. Beyond Compare can compare a local directory and a remote directory via FTP. Very handy when moving files to remote servers!
Whether you use one of the many freely available utilities or purchase one of the more advanced applications a diff tool is essential in any developers toolbox.