Need Software to compare two text files

The classical Un*x way of doing that is diff:

diff file1 file2

A more visual way for vim users is to do vimdiff:

vimdiff file1 file2

Finally, there is diffuse:

sudo apt-get install diffuse
diffuse file1 file2

Here is an example diffuse window:

You clearly see the differences between the two text files. Using the blue arrows on the top that go up or down you can move between the differences found. The blue arrows on the top that go left and right can be used to move the text from left to right and the other way round. The icons with two little blue arrows are used to merging the two files.

If you double click, you can directly edit the text.

Just to make life more interesting, you will get an upvote if you guess correctly what is this data in the above picture :-)

There is Meld Diff Viewer. Meld is a graphical user interface tool for comparing text files and their contents. You can find instructions on how to install and use it here.

There is also the command line tool diff

Diff syntax:

diff first_file_to_compare second_file_to_compare