How do I get the list of changed files in my pipe?

[J. Longman]

I'd like to get the list of changed files and only scan them.  Ideally it would be all files in the PR but it could be compared to a specific branch (e.g. master).

I really want to isolate the case of an incremental build over a full build because the difference is an order of magnitude in seconds, and this isn't a big repository.

Note, this is in a pipe, not a pipeline. (Well, of course the pipe is called from a pipeline, but you know what I mean).

if I do a git diff HEAD..master (or origin/master) it doesn't work.

If I look in .git/refs/heads, I don't have any other reference than the current branch.

if I do a git fetch:

+ git fetch
fatal: unable to access 'http://bitbucket.org/mvcode/mv-devops/': Failed to connect to localhost port 29418: Connection refused

If I set the ssh or http origin then I get errors. (have to re-run these to get the errors.)

ssh:

+ git remote set-url origin git@bitbucket.org:mvcode/mv-devops.git
+ git ls-remote
Host key verification failed.
fatal: Could not read from remote repository.
Please make sure you have the correct access rights
and the repository exists.

http:

+ git remote set-url origin http://bitbucket.org/mvcode/mv-devops
+ git ls-remote
fatal: unable to access 'http://bitbucket.org/mvcode/mv-devops/': Failed to connect to localhost port 29418: Connection refused

(that host mapping to localhost is cute, it would be nice if it did the right thing in pipes and used the host.docker.internal instead).

If I set it to the pipe host.docker.internal:29418 value I get errors.

+ git remote set-url origin http://host.docker.internal:29418
+ git ls-remote
fatal: unable to access 'http://host.docker.internal:29418/': The requested URL returned error: 502

If I try to use the API to do a diffstat, as I've seen elsewhere, I get you must be admin or have write access, which A) doesn't make sense, I'm reading, B) I _do_ have that access (the pipe may not).

++ curl -s --proxy http://host.docker.internal:29418 --request GET http://api.bitbucket.org/2.0/repositories/mvcode/mv-devops/diffstat/f7f6a6bca8181653f3e4208fbd3ac6874942d36d
Access denied. You must have write or admin access.

So it looks like I can probably auth my way in, but I feel that the files that changed should be intrinsic knowledge to a PR.  It should be easily available and there shouldn't be a need for auth as it's a read only operation on state that you have an even more complete access to.  Ideally this would be available without an API or git operation, like in a well-known location.

[J. Longman · Accepted solution]

# save just in case
BACKUP_PROXY=$(git config "http.${BITBUCKET_GIT_HTTP_ORIGIN}.proxy")
# replace
git config "http.${BITBUCKET_GIT_HTTP_ORIGIN}.proxy" http://host.docker.internal:29418
# fetch
git fetch origin "${DEFAULT_BRANCH}"
mapfile -t RAW_FILE_ARRAY < <(git -C "${GITHUB_WORKSPACE}" diff --name-only "FETCH_HEAD..${GITHUB_SHA}" --diff-filter=d 2>&1)
# restore just in case
git config "http.${BITBUCKET_GIT_HTTP_ORIGIN}.proxy" "$BACKUP_PROXY"

 This feels like a bug.

[J. Longman]

see accepted answer