What is a “Diff”?
In the field of computing, diff refers to a utility that compares the differences between two particular files. This comparison utility is used when one wants to see what changes were made to a file from its original version to a newer version of it. “Diff” also refers to the output of this comparison utility but is sometimes referred to as a patch, indicating that it can be applied to the Unix OS or Linux program patch.

The diff utility actually comes out in a package containing diff, diff3, sdiff, and cmp programs. “diff3” is involved with comparing and showing the differences between 3 particular files. “sdiff” meanwhile can merge two particular files interactively. “cmp” on the other hand is the one that presents the line numbers and offsets in which two particular files differ. It is also capable of displaying the characters that are different between two particular files, side by side.

Diff as a comparison utility was developed by Unix OS in the early parts of 1970s. Its final version came along with UNIX’s 5th edition which was released in the year 1974. This particular version was written in whole by Douglas McIlroy. In 1976, this particular research was published by McIlroy and James Hunt, who also had developed a diff prototype. Because of this collaboration, the algorithm used in their paper was named the “Hunt-McIlroy” algorithm”. Diff’s development was also said to be influenced by previous comparison utility programs like GECOS and the “proof” program by Mike Lesk.

The diff comparison utility was used when one wants to compare source codes and mark-ups for tech documents. It can also be used to compare file-system listings, verify debugging output, and analyze assembly codes. Since its release in the early 1970s, there were a couple of updates and improvements to the diff comparison utility. These updates included a better core algorithm, new formats or output displays, and new and improved features to the command.