Send Commit message on Acquia Hook by Slack
The commit message isn't passed in to the script, so you have to get it from somewhere else. I'm not sure if there is a git repository available to the cloud hook scripts on Acquia's cloud servers in general (it seems like there must be, but...I can't find an answer about where it is in their docs). You do have the repository url and the branch/tag, so you could try a shallow clone of the tag to get the data:

git clone --depth 1 --branch $deployed_tag $repo_url clonedirectory
cd clonedirectory
commit_message=`git show -s --format=%B`
...
echo $commit_message


You can use the $commit_message variable in the slack commands.

Of course...you have to figure out how to authenticate to the git repo and I'm not sure what's a great solution there.

Really I hope someone will reply with the location of a git clone that's available on cloud servers.