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You are very much correct that `Alt-.` with modifiers can do more than what has been described, it is however important to note that the behavior of `Alt-<key>` changes heavily both between zsh and bash, but also between `vi-mode` and `emacs-mode`.
For instance, zsh will switch to `vi-mode` depending on env variables such as `$EDITOR`, making `Alt-<key>` unavailable in that regard.
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It's also worth noting that `ctrl-alt-e` is _not_ a zsh default, though it is a fair point that it could have been added in the below linked section:
https://refp.se/articles/your-shell-and-the-lazy-exclamation...
For what it's worth, I had troubles finding a proper scope for the article contents — and with that the lines became a bit blurry in terms of what to include, and what not to include.
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I really appreciate constructive comments like yours, and hope it together with the article can help future shell ninjas!
What you can do with what is always hard to answer given that all roads lead to Rome, though some roads have more turns than others.
This will expand the event designator after you type space to end it. So you type “!” “$” “space” and the designated argument expands in-place.
No, it isn't limited to just that. Alt-0 alt-. will give you the zeroth "argument" (the program), alt-1 alt-. will get you the next (the program's first argument), etc. Negative arguments count back from the end: alt-- 1 alt-. will get you the argument before the last one (note that alt is held for the "-" but not the digit).
When you do use event designators, ctrl-alt-e (or alt-^) is critical. It expands all the ! codes inline to what they refer to, so you can see what you're doing before you hit enter, and as you're constructing the command too.