What does 'd' mean in diff output?

That's a great question! However, in the diff output shown in the current step, which is:

1c1
< this is file1
---
> this is file2

You are seeing a c (for "change"), not a d.

The diff command has a few different indicators:

• c (change): Means lines in the first file need to be changed to match lines in the second file.
• a (add): Means lines need to be added to the first file to match content in the second file.
• d (delete): Means lines need to be deleted from the first file to match content in the second file.

If you encountered a d in a diff output, it would typically look something like 1d0 or similar, indicating that line 1 of the first file should be deleted.

For example, if file1 had:

this is file1
this is an extra line

And file2 had:

this is file1

Then diff file1 file2 might show output with d to indicate the "extra line" in file1 should be deleted.

In our current exercise, because both file1 and file2 have a single line, but the content of that line is different, diff shows it as a 1c1 (change on line 1).

Keep up the great work! Let me know if anything else comes up.