How does the diff command show differences in file content?

The diff command shows differences in file content by comparing two files line by line and outputting the changes between them. The output typically includes:

1. Lines that are different:

   • Lines that are present in one file but not the other are marked with a > or < symbol.
   • Lines that have been changed are shown with a - for the line removed and a + for the line added.

2. Context lines:

   • By default, diff shows a few lines of context around the changes to provide clarity on where the differences occur.

For example, if you run diff file1.txt file2.txt, the output might look like this:

1c1
< This is a line in file1.
---
> This is a line in file2.

In this output:

• The < indicates a line from file1.txt.
• The > indicates a line from file2.txt.
• The c indicates that the line has changed.

Using options like -u or -c can change the format to a unified or context format, respectively, which provides more context around the differences.