As far as I know, you cannot execute any code* in .tm_properties.

A quick mockup of the script that would turn a .gitignore into a blob, would look like this:

paste -d, -s .gitignore

In theory this could be integrated into some build script to update your .tm_properties, but then TextMate would need to be restarted* to pick up the changes.

I suggest this little gem instead:

If you hold option (⌥) when using the (new) remove button to prune folder search results then the glob will be extended to exclude the undesired path, so that future searches exclude it by default.

Graham P Heath

*: IIRC / Correct me if I’m wrong