Last Updated: 2024-05-01

I wanted to find how a certain configuration option changed my Webpack output, which consisted of two files: file1 and file2 (I will use text instead of JavaScript in the examples)

file1:

this is the original text  
line2
line3
line4
happy hacking !

file2 (line3 is deleted and the last line was added)

this is the original text  
line2  
line4  
happy hacking !  
GNU is not UNIX

Normal diff format

Output of $ diff file1 file2

3d2  
< line3  
5a5  
> GNU is not UNIX  

• < means first file (file1)
• > means second file (file2)
• 3d2 and 5a5 denote line numbers affected and which actions were performed
  • d means "deleted"
  • a means "appended"
  • c means "changed" (not shown)
  • number on left of letter means first file, right means second
  • 3d2 tells you that the 3rd line in file1 was deleted and has the line number 2 in file2 (or better to say that after deletion the line counter went back to line number 2).
  • 5a5 tells you that the we started from line number 5 in file1 (which was actually empty after we deleted a line in previous action), added the line and this added line is the number 5 in file2

Unified diff format

$ diff -u file1 file2

output:

--- file1        2013-07-06 17:44:59.180000000 +0200  
+++ file2        2013-07-06 17:39:53.433000000 +0200  
@@ -1,5 +1,5 @@  
 this is the original text  
 line2  
-line3  
 line4  
 happy hacking !  
+GNU is not UNIX  

• Here - in the leftmost column denotes the lines, which were deleted from file1 and + denotes the lines, which were added.
• @@ -1,5 +1,5 @@ represents a hunk. The part -1,5 relates to file1 and the part +1,5 to file2 They tell us that diff will show a piece of text, which is 5 lines long starting from line number 1 in file1.txt. And the same about the file2.txt - diff shows us 5 lines starting from line 1.

Here's another example:

output:

13. @@ -9,3 +9,4 @@
14.  source /home/vagrant/.profile  
15.  
16.  nvm install node  
17. +nvm alias default node

• This shows the hunk from line 9 on file1 that is 3 lines long there, and from line 9 in file2 but is 4 lines long there.
• Everything in lines 14-17 of this output (NOT the original files) remains the same. However nvm alias default node was added.

Colored output

To get colored diff, pipe into vim: $ diff application*.js | nvim -

References

• https://unix.stackexchange.com/questions/81998/understanding-of-diff-output