diff output understanding
diff is a fantastic tool to compare files or even directories line by line which can be found in your command line out of box.
Normally, we could learn its usage from
man diff. But this is just a basic manual lacking of detailed explanation. The full documentation for
diff is maintained as a
info manual. If the
diff programs are properly installed at your site, the command
info diff should give you access to the complete manual.
info is rather rare now, so we might need to learn how to use info.
If we diff two files such as
diff <file1> <file2>, then,
< denotes lines in
> denotes lines in
But what are the meanings of these characters:
The following is the format description in
Detailed Description of Normal Format ------------------------------------- The normal output format consists of one or more hunks of differences; each hunk shows one area where the files differ. Normal format hunks look like this: CHANGE-COMMAND < FROM-FILE-LINE < FROM-FILE-LINE... --- > TO-FILE-LINE > TO-FILE-LINE... There are three types of change commands. Each consists of a line number or comma-separated range of lines in the first file, a single character indicating the kind of change to make, and a line number or comma-separated range of lines in the second file. All line numbers are the original line numbers in each file. The types of change commands are: `LaR' Add the lines in range R of the second file after line L of the first file. For example, `8a12,15' means append lines 12-15 of file 2 after line 8 of file 1; or, if changing file 2 into file 1, delete lines 12-15 of file 2. `FcT' Replace the lines in range F of the first file with lines in range T of the second file. This is like a combined add and delete, but more compact. For example, `5,7c8,10' means change lines 5-7 of file 1 to read as lines 8-10 of file 2; or, if changing file 2 into file 1, change lines 8-10 of file 2 to read as lines 5-7 of file 1. `RdL' Delete the lines in range R from the first file; line L is where they would have appeared in the second file had they not been deleted. For example, `5,7d3' means delete lines 5-7 of file 1; or, if changing file 2 into file 1, append lines 5-7 of file 1 after line 3 of file 2.
5d4: line 5 of
<file1>was deleted, line 4 is where it would have appeared in
<file2>if it was not deleted. This means that the original line 6 of
<file1>is line 5(4+1) of
<file2>which looks like original line 5 of
<file1>is at line 4 in
<file2>(Just image!). The comparasion picture as below:
9,23c8: change lines 9-23 of
<file1>to read as line 8 of
4,33d3: line 4-33 of
<file1>were deleted, line 3 is where it would have appeared in
<file2>if they were not deleted as next common line is 4 in
5a6: Add line 6 of
<file2>after line 5 of
<file1>. The comparasion picture as below: