Use Regex Capture Group in Replacement

[Orthopoxvirus]

Hi all,

is there a way to use a regex capture groups in the replacement in modify?

Example:
beet modify -a "path::^/music/some-path/(\d{3})\_(.*)" album="Prefix $1: $2"
which should set the album of "/music/some-path/123_Episode Title" to "Prefix 123: Episode Title"

Edit: I already tested: $1, \1, \g<1> as replacements

Cheers
Michael

[Hikari-Tsai]

No: capture groups from a query regex are not exposed to modify templates. A query only decides whether an item/album matches; the replacement template is then evaluated from model fields, so $1, \1, and \g<1> have no capture context.

For this transformation, an inline field can perform the regex and return the new value:

plugins: inline

album_fields:
  episode_album: |
    import re
    match = re.search(r"/music/some-path/(\d{3})_(.*?)(?:/|$)", path)
    return f"Prefix {match.group(1)}: {match.group(2)}" if match else album

Preview it first:

beet ls -a -f '$album -> $episode_album' 'path::^/music/some-path/'

Then apply it:

beet modify -a 'path::^/music/some-path/' 'album=$episode_album'

Quoting the assignment is important so the shell does not expand $episode_album.