update
1 Cheat on Unified Diff command (diff -u)
Unified diff gives you slightly different syntax than just a straight diff.
I ususally stick to the straight diff command, but -u gives more precise
line number references. Also, git uses the unfied diff output in git diff
commands
1.1 unified diff output meaning
When run in unified diff mode with the -u option you get:
First two lines are
--- from-file from-file-modification-time +++++ to-file to-file-modification-time
--- from-file from-file-modification-time +++ to-file to-file-modification-time
Next come one or more chunks of differences with this syntax:
@@ from-file-line-numbers to-file-line-numbers @@ line-from-either-file line-from-either-file…
If a chunk and its context contain two or more lines, its line numbers look
like ‘start,count’. Otherwise only its end line number appears.
The lines common to both files begin with a space character.
The lines that actually differ between the two files have either a + or a -
characters in the left print column:
‘+’ A line was added here to the first file. ‘-’ A line was removed here from the first file.
Here is a larger example:
$ diff -u 1stfile 2ndfile --- 1stfile 2020-05-22 11:32:48.000000000 -0400 +++ 2ndfile 2021-02-02 16:20:15.000000000 -0500 @@ -1,12 +1,10 @@ # The first file has twelve lines in this block # The second file ends up with only 10 lines in this block # -# macOS Notice +# macOS Notice This line was changed on the 2nd file. # # This file is not consulted for DNS hostname resolution, address # resolution, or the DNS query routing. # -# This line is in the first file, but will be removed in 2nd file -# This line also will be removed in 2nd file. # @@ -17,3 +15,5 @@ nameserver 208.67.220.220 You can get so confused that you'll start in to race down long wiggled roads at a break-necking pace +# And # Two new lines added to second file, +# On and on . # hence now we are looking at a block of 5 lines in 2nd.