Reproduce previous stdout output without running previous command

[Daniel Underwood]

OK, this is perhaps a weird question, capable of being very confusing.
 So let's take a "for instance".

Suppose I run something like the Linux command "fdupes" on a directory
with many large files.  This operation will take considerable time to
complete.  When it completes, a lot of output is send to stdout
(displayed on the terminal).

Further suppose that after running the command, I decide I want to
save the output to a text file, so I can analyze the results outside
of the terminal.  What can I do? Well, I can do a traditional
"copy-and-paste", or I could re-enter the previous command and send it
to a text file (which I ought to have done in the first place).

But is there another option?  Is there some variable (such as,
hypothetically, $output[n], where n=some integer index) that I could
use to store the results in a text file?  Such an option might look
like the following:

$ fdupes -r ~/directorywithlotsoflargefiles

(.....lots of output, woops, should have sent to a text file!....)

$ output[1] >> ~/textfile.txt

Hopefully this has made (some) sense.