How can the 'join' command be configured to include unpairable lines from file2?

To include unpairable lines from file2 when using the join command, you can use the -a option followed by the number 2. This option tells join to include all lines from file2, even if they do not have a matching line in file1.

Here’s an example command:

join -a 2 file1.txt file2.txt

In this command, file1.txt is the first file and file2.txt is the second file. Lines from file2.txt that do not have a match in file1.txt will be included in the output.