I've been a (blind) user of bash's "caret replacement" for ages, but have occasionally wondered how to replace all occurences of a word, rather than the first.
$ echo "foo bar baz foo" foo bar baz foo $ ^foo^quux echo "quux bar baz foo" quux bar baz foo
The answer is to use the more robust event designator syntax: !!:gs/search/replace/
$ echo "foo bar baz foo" foo bar baz foo $ !!:gs/foo/quux/ echo "quux bar baz quux" quux bar baz quux
While on the topic of esoteric bash commands, here's another good one. You may (?) know of !$ which references the last argument of the last command in history. That's just an alias for !!:$, which shows the more general form of the command. You can access any argument of any command in history.
$ echo "test" > /tmp/blah.txt $ cat !!:3 cat /tmp/blah.txt test
There's lots more. In particular, you can operate on any command in history, not just the last one (!!). See the bash manual link in the references below.