Speed
It boggles the mind. How can computers be that fast? The line below does several steps.
* removes an existing output file.
* It tells the difference between tow text files. This alone is amazing because one file is 15000 lines and the other is 25000 lines. That would take me a lifetime.
* the difference report is then fed into a command to only give the lines that start with "> " greater than and a space. Then, the sed command strips the "> " off the output. This way, I only get the delta. the output file is 8000 lines or so long.
How long does it take to do it? If I tap the enter key, it's done before I can let it up again.

rm diff2.txt && diff out_before.txt out_after.txt | egrep '^>\ ' | sed '-e s%> %%g' > diff2.txt