In a diff output, what does the change '2a3' mean?

• A. It changes lines 2-4 in the original file to match lines 2-4 in the new file.
• B. It appends the content of line 3 from the new file after line 2 in the old file.
• C. It deletes line 4 from the original file.
• D. It adds a new file after line 2.

Answer: (B)

In diff notation, the letter a stands for append. The sequence 2a3 means you insert something after line 2 of the original file. Specifically, you take line 3 from the new file and place it right after line 2 in the old file. So it’s an insertion of a single line, not a replacement or deletion of a block, and it doesn’t create a new file—just adds content after that position. For example, if the original has lines 1, 2, 3, 4 and the new file’s line 3 is “X,” applying this would yield 1, 2, X, 3, 4.