More than you really wanted to know about patch
http://lists.landley.net/pipermail/toybox-landley.net/2019-January/010049.html [lists.landley.net]
2019-01-17 23:35
Back in the 1980’s somebody invented diff -u (“unified diff format“) as a more human readable alternative o the <old >new lines format you get without the -u, and then Larry Wall whipped up a program to reverse the process and use saved diff -u output to modify a file (which was mind-blowing at the time). As far as I can tell the format wasn’t really meant for that, and was made to work with heuristics and hitting it with a rock, but Larry _did_ go on to invent Perl...
source: L