Ah yes. My custom Node script (which I hope it's OK to paste below) strips
the beginnings and ends of the input. I suppose that it could be done
already on the Elisp side, which would take care of interpreting the
$-signs as envvars too.

const katex = require('katex')
let input = process.argv[2].trim()
let disp = true
if (input.slice(0, 2) === '\\[' || input.slice(0, 2) === '$$') {
  input = input.slice(2, -2)
}
else if (input.slice(0, 2) === '\\(') {
  input = input.slice(2, -2)
  disp = false
}
else if (input.slice(0, 1) === '$') {
  input = input.slice(1, -1)
  disp = false
}
else {
  console.error("Did you quote the input correctly?")
  process.exit(1)
}
console.log(katex.renderToString(
  input, {
    displayMode: disp,
    output: 'mathml',
    trust: true,
    strict: false,
    throwOnError: false,
  }
))

On Wed, Feb 21, 2024 at 15:38 Max Nikulin <manikulin@gmail.com> wrote:

> On 19/02/2024 02:36, Martin Edström wrote:
> > +Since this is a shell-command, remember to use single-quotes
> > +around \\='%i\\=', not double-quotes!  Else a math fragment such
> > +as \"$y = 200$\" gets butchered into only \" = 200\"."
>
> I am afraid, the code, not the docstring must be fixed. I have not tried
> it, but I expect an issue with
>
>      Test \(f' = df/dx\)
>
> So `shell-quote-argument' is necessary and quotes around %i must be
> stripped similar to %s in mailcap entries in `org-open-file'.
>
> Notice that dollar-math $x = y$ is not recommended and considered as
> obsolete syntax. Use \(x = y\) or \[x = y\] (the latter for display math).
>