Re: How to do history expansion on a string?

[Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx>]

On Wed, Feb 12, 2025 at 4:00 PM vapnik spaknik <vapniks@xxxxxxxxx> wrote:
>
> Is it possible to expand a bang pattern stored in a string? (e.g. "!123:2").

It depends on when/where/how you want to "expand" it.  If you mean
expand all the way from !123:2 to ending up with the second word from
history event 123, there's no direct way to use bang-references
without being able to execute zle widgets to modify the command
buffer.

> I've tried the zpty and zsocket modules

If the shell spawned in zpty has exactly the same history as the shell
where you want the expansion, you should be able to do this by using
the :p history modifier to get the result of history expansion printed
without actually executing a command, so theoretically you can push
something into zpty and read it back again expanded, but if you can do
all that you can probably also use a zle widget.

> I want to make a convenience function for selecting bangs using fzf

I have no idea if fzf could drive that, so I'll explain a few things
that are possible and let you try to work it out from there.

Case 1: If actual bang-text such as !123:2 etc. is present as part of
a command line (ZLE $BUFFER) then invoking the expand-word widget at
any cursor position will expand all such references, rewriting the
contents of the buffer.  Note single quotes around a word prevent
history expansions, but double quotes do not.

Case 2: If the bang-text is stored in a parameter and a reference to
that parameter is on the command line, then invoking expand-word with
the cursor on that specific word will edit the parameter value into
the command line (as with any parameter reference), and now you're
back to case 1.  By default, however, the result will insert \! so the
reference form needs to account for that and for any quoting around
it.  E.g., ${~bangtext} is sufficient for an unquoted reference, but
with double quotes like "${~bangtext}" the backslash will reappear.

Case 3: The bang-text is in a parameter and you're able to use a zle
widget to modify $BUFFER, you can insert the value directly with
something like LBUFFER+=${bangtext} to get a command line like case 1,
and then invoke "zle expand-word".

The alternative to any of that is to write the desired expansion as a
reference to $history.  E.g., !123:2 is ${history[123][(w)2]},
although not all conversions are that simple.