One day, I'm not sure exactly when, I stumbled over the standard readline binding of M-. for 'yank-last-arg'. The description you can find in your local readline manpage may be a little abstract, so here's the simplified version: M-. inserts whatever was the last word on the previous command line into your current command line.

Did you perhaps type:

$ ls *some*[Cc]omplex*pattern

and now you want to grep through files matching that pattern? Easy; type ' grep thing M-. ' and you'll wind up with ' grep thing *some*[Cc]omplex*pattern '.

(You can also use M-_ , according to the manpage.)

This turns out to not be the only potentially useful standard readline binding that I wasn't aware of, so here's my current little collection.

M-C-y is 'yank first argument'. With an argument, both it and M-. are 'yank nth argument', but I'm not sure I'd ever do that instead of some form of line editing. (Providing numeric arguments is a bit awkward in readline and we're into the same 'counting words' problem territory that I have with Vi. It's mentally easier to reshape a command line than count out that I want the third, fourth, and sixth argument.)

is 'yank first argument'. With an argument, both it and are 'yank nth argument', but I'm not sure I'd ever do that instead of some form of line editing. C-_ or C-x C-u is incremental undo.

or is incremental undo. M-r reverts the line to its original state. This is probably mostly useful if I've accidentally modified a line in the history buffer and want to discard those changes to revert it to its pristine as-originally-typed state.

In Bash specifically (although not necessarily other things that use readline), you can force certain completions regardless of bad attempts to be clever. These are:

M-/ for filename completion

for filename completion M-! for command name completion

for command name completion M-$ for variable name completion

for variable name completion M-@ for hostname completion

for hostname completion M-~ for user name completion

All have C-x <char> versions that list all the possible completions. The keys for these are reasonably related to what you're forcing a completion for, so I have at least some chance of remembering them in the future.