Ultsnips transformation not working as desired

[kontrapunktstefan]

I have written the following snippet for UltiSnips in Vim. With this snippet I want to add an apostrophe to all lilypond pitches:

snippet 1 "lilypond pitches with apostophes"
$1
${1/\w+\s*/$0'/g}
endsnippet

When I execute it, however, the text appears twice:

c d e
c' d' e'

I just want the 2nd line

I've tried snippet 1 "lilypond pitches with apostophes"

snippet 1
${1/\w+\s*/$0'/g}
endsnippet

but this gives an error:

UltiSnips Error:

Tabstop 1 is not known but is used by a Transformation

[SirVer]

Hey, you cannot change what you typed yourself, that is a limitation of Vim, unfortunately. The best you can do is something like this:

snippet apo "lilypond pitches with apostophes"
`!p
lines = []
for idx, line in enumerate(snip.v.text.splitlines()):
    lines.append(" ".join(f"{a}'" for a in line.split()))
snip.rv = "\n".join(lines)
`
endsnippet

You use it like this:

1. type out your line c d e
2. Visual select the line (i.e. in normal mode, V)
3. expand (not sure what your trigger is, maybe <tab>), this will remove the text
4. type apo<tab> or whatever your expand trigger is
5. output line is c' d' e'.

Hope that helps