[Rpm-maint] [rpm-software-management/rpm] Any way to work around %gsub's (Lua-originating) escaping requirements regarding the input string? (Discussion #3826)

[Frank Dana]

**#TIL**, while trying to write a `%{gsub}` call to manipulate a package `%{version}`, that `%{gsub}` won't properly handle periods unless they're escaped not only in the pattern arguments, but also in the _source string_!

That restriction appears to come from Lua itself:

```lua
> string.gsub("1.2.3", ".", "_")
_____	5
> string.gsub("1.2.3", "\\.", "_")
1.2.3	0
> string.gsub("1\\.2\\.3", "\\.", "_")
1_2_3	2
```

But it most certainly carries over to RPM:

```console
$ rpm --eval '%{gsub 1.2.3 . _}'
_____

$ rpm --eval '%{gsub 1.2.3 \\. _}'
1.2.3

$ rpm --eval '%{gsub 1\\.2\\.3 \\. _}'
1_2_3
```

That obviously becomes a problem when trying to `%{gsub %{version} ...)` because while escaping the patterns is no problem, unless I'm missing something obvious there's no way to easily escape any of the dots contained in `%{version}`. (We sure can't use `%{gsub}` to do it!)

It almost feels like we need a `%{regexscape:}` or `${patescape:}` to go with `%{quote:}` and `%{shescape:}`, because neither of those will DTRT here, either.

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