Writing a de-psfagger

[Karl Berry]

          kpsewhich -var-brace-value TEXMF

    seems to have the entries separated by colon (:). Mine is separated by
    commas (,). What is the difference? The shell?

No, kpsewhich has no idea what shell you are using.
Are you sure you are using -var-brace-value and not -var-value?

$ kpsewhich -var-brace-value TEXMF
/u/karl/.texlive2019/texmf-config:/u/karl/.texlive2019/texmf-var:...

$ kpsewhich -var-value TEXMF
{{}/u/karl/.texlive2019/texmf-config,/u/karl/.texlive2019/texmf-var,...}

The whole point of -var-brace-value is to do brace expansion, thus the
comma-separated elements in braces become a flat colon-separated list.