In informal (spoken) Irish English, 'but' does not appear in initial position of the clause that it introduces, but comes after it:

- That there was Jenny’s wedding, but.

- We haven’t got the Spains, but.

- “You’re not, but."

- “Not this time, but." = But not this time.

- “Something personal, but."

- "Another thing, but."

Etc.

All examples from Tana French - Broken Harbour (2012).

Here 'but' seems to be used with the meaning of 'however' (which is more likely to be used in writing).