diff3 command compares three files and outputs descriptions
of their differences. Its arguments are as follows:
diff3 options... mine older yours
The files to compare are mine, older, and yours.
At most one of these three file names may be
diff3 to read the standard input for that file.
An exit status of 0 means
diff3 was successful, 1 means some
conflicts were found, and 2 means trouble.