Reference:
https://unix.stackexchange.com/questions/252927/what-do-the-numbers-in-the-line-mean-in-output-of-diff A unified diff file shows differences between two files. Each chunk of changes starts with a line that provides the range of lines affected in the original and new files. The correct format is:
The - symbol indicates the starting line number and the number of lines in the original file.
The + symbol indicates the starting line number and the number of lines in the new file.
@@ -88,10 +88,6 @@ shows that the original file has a chunk starting at line 88 with 10 lines, and the new file has a chunk starting at line 88 with 6 lines.
Reference: Unified Diff Format