Automatically capture output of last command into a variable using Bash?

This is a really hacky solution, but it seems to mostly work some of the time. During testing, I noted it sometimes didn't work very well when getting a ^C on the command line, though I did tweak it a bit to behave a bit better.

This hack is an interactive mode hack only, and I am pretty confident that I would not recommend it to anyone. Background commands are likely to cause even less defined behavior than normal. The other answers are a better way of programmatically getting at results.

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That being said, here is the "solution":

PROMPT_COMMAND='LAST="`cat /tmp/x`"; exec >/dev/tty; exec > >(tee /tmp/x)'

Set this bash environmental variable and issues commands as desired. $LAST will usually have the output you are looking for:

startide seth> fortune
Courtship to marriage, as a very witty prologue to a very dull play.
                -- William Congreve
startide seth> echo "$LAST"
Courtship to marriage, as a very witty prologue to a very dull play.
                -- William Congreve

I don't know of any variable that does this automatically. To do something aside from just copy-pasting the result, you can re-run whatever you just did, eg

vim $(!!)

Where !! is history expansion meaning 'the previous command'.

If you expect there to be a single filename with spaces or other characters in it that might prevent proper argument parsing, quote the result (vim "$(!!)"). Leaving it unquoted will allow multiple files to be opened at once as long as they don't include spaces or other shell parsing tokens.