Commit hash of the revision about to be deployed? - capistrano

Question

I want to add a hook that logs something to the effect of "Hey, I'm about to deploy such-and-such commit." Something like:
before "deploy:update_code" do
logger.info "Deploying #{revision}"
end
Except "revision" in this context seems to yield a ref name (i.e. "master") rather than a commit ID. What construct can I use to get the sha1?

Answer 1

To get the ref, you'll need to shell out to Git:
Here's an example from one of my own projects, where master is fully up-to-date and pushed, and my clean_architecture branch isn't.
~/api git:(clean_architecture) $ git show-ref master
349dabbffec0713ac0fc70cf991dbaff6412ad2b refs/heads/master
349dabbffec0713ac0fc70cf991dbaff6412ad2b refs/remotes/origin/master
~/api git:(clean_architecture) $ git show-ref clean_architecture
14afae560ace128a13336ca01ff2391b678fadaf refs/heads/clean_architecture
bc78906ad0b2814dbc6225b2e14155b66eedffd0 refs/remotes/origin/clean_architecture
Taking that on-board, I'd suggest something like the following to grab the remotely pushed ref hash (as that's the only one the Capistrano 3 can see, Capistrano will do a check like this internally, but you can't access the ref, and will complain if these two values differ, anyway)
First, on the command line:
$ git show-ref clean_architecture | tail -1 | cut -f1 -d ' '
bc78906ad0b2814dbc6225b2e14155b66eedffd0
$ git show-ref clean_architecture | tail -1 | awk '{print $1}'
bc78906ad0b2814dbc6225b2e14155b66eedffd0
(there's about a million ways to do this on linux)
Secondly in Ruby:
$ irb --simple-prompt
>> `git show-ref #{fetch(:branch)}`
=> "349dabbffec0713ac0fc70cf991dbaff6412ad2b refs/heads/master\n349dabbffec0713ac0fc70cf991dbaff6412ad2b refs/remotes/origin/master\n"
Which let's us know we can split this up really easily in Ruby land, and not need cut or awk:
$ irb --simple-prompt
>> `git show-ref #{fetch(:branch)}`.split.first
That should be pretty close, and pretty-portable (where as cut and awk, and splitting that up in the shell with pipes, etc is quite *nix specific and unlikely to work well on Windows)
Drop that in your before task, and you should be set.