Three-way mergeA three-way merge is performed after an automated difference analysis between a file 'A' and a file 'B' while also considering the origin, or parent, of both files (usually the parent is the same for both). This type of merge is generally only available through the use of supporting revision control systems where such a parent would normally exist. The merge tool examines the differences and patterns appearing in the changes between both files as well as the parent, building a relationship model to generate a merge of files 'A', 'B', and the parent, 'C' to produce a new revision, 'D'.This merge is the most reliable and has performed well in practice. It has also required the least amount of user intervention, and in many cases, requiring no intervention at all (depending upon the complexity of the merge) making the process available for task automation.
如果是最简单的一个文件追加到另一个文件的后面, 那很简单
控制台下面，copy /b aa.txt +bb.txt cc.txt
工具很多，可惜都是国外的软件。
Araxis Merger好像不错，CSDN上也有下载
http://en.wikipedia.org/wiki/Comparison_of_file_comparison_tools
可以自动合并，且支持联网