first_attempt.txt

~/src/chef-repo $ knife cookbook site vendor mysql -d
WARNING: No knife configuration file found
Installing mysql to /var/chef/cookbooks
ERROR: The cookbook repo path /var/chef/cookbooks does not exist or is not a directory

second_attempt.txt

~/src/chef-repo $ knife cookbook site install couchdb -o ./cookbooks/
WARNING: No knife configuration file found
Installing couchdb to ./cookbooks/
Checking out the master branch.
Pristine copy branch (chef-vendor-couchdb) exists, switching to it.
Downloading couchdb from the cookbooks site at version 0.14.0 to ./cookbooks/couchdb.tar.gz
Cookbook saved: ./cookbooks/couchdb.tar.gz
Removing pre-existing version.
Uncompressing couchdb version ./cookbooks/.
ERROR: Chef::Exceptions::ShellCommandFailed: Expected process to exit 0, but it exited with 1
---- Begin output of tar zxvf ./cookbooks/couchdb.tar.gz ----
STDOUT: 
STDERR: tar: Error opening archive: Failed to open './cookbooks/couchdb.tar.gz': No such file or directory
---- End output of tar zxvf ./cookbooks/couchdb.tar.gz ----
Ran tar zxvf ./cookbooks/couchdb.tar.gz returned 1

third_attempt.txt

~/src/chef-repo $ knife cookbook site install couchdb -o ./
WARNING: No knife configuration file found
Installing couchdb to ./
Checking out the master branch.
Pristine copy branch (chef-vendor-couchdb) exists, switching to it.
Downloading couchdb from the cookbooks site at version 0.14.0 to ./couchdb.tar.gz
Cookbook saved: ./couchdb.tar.gz
Removing pre-existing version.
Uncompressing couchdb version ./.
removing downloaded tarball
1 files updated, committing changes
Creating tag cookbook-site-imported-couchdb-0.14.0
Checking out the master branch.
Updating a3bec38..64eea23
Fast-forward
 couchdb/README.md                          |   61 ++++++++++
 couchdb/attributes/default.rb              |   22 ++++
 couchdb/files/default/couchdb.init         |  168 ++++++++++++++++++++++++++++
 couchdb/metadata.json                      |   55 +++++++++
 couchdb/metadata.rb                        |   24 ++++
 couchdb/recipes/default.rb                 |   49 ++++++++
 couchdb/recipes/source.rb                  |   93 +++++++++++++++
 couchdb/templates/default/port_couchdb.erb |    2 +
 8 files changed, 474 insertions(+), 0 deletions(-)
 create mode 100644 couchdb/README.md
 create mode 100644 couchdb/attributes/default.rb
 create mode 100644 couchdb/files/default/couchdb.init
 create mode 100644 couchdb/metadata.json
 create mode 100644 couchdb/metadata.rb
 create mode 100644 couchdb/recipes/default.rb
 create mode 100644 couchdb/recipes/source.rb
 create mode 100644 couchdb/templates/default/port_couchdb.erb
Cookbook couchdb version 0.14.0 successfully installed
Installing erlang to ./
Checking out the master branch.
Creating pristine copy branch chef-vendor-erlang
Downloading erlang from the cookbooks site at version 0.8.2 to ./erlang.tar.gz
Cookbook saved: ./erlang.tar.gz
Removing pre-existing version.
Uncompressing erlang version ./.
removing downloaded tarball
1 files updated, committing changes
Creating tag cookbook-site-imported-erlang-0.8.2
Checking out the master branch.
Updating 64eea23..60fd4d6
Fast-forward
 erlang/attributes/default.rb |    1 +
 erlang/metadata.json         |   36 ++++++++++++++++++++++++++++++++++++
 erlang/metadata.rb           |   11 +++++++++++
 erlang/recipes/default.rb    |   27 +++++++++++++++++++++++++++
 4 files changed, 75 insertions(+), 0 deletions(-)
 create mode 100644 erlang/attributes/default.rb
 create mode 100644 erlang/metadata.json
 create mode 100644 erlang/metadata.rb
 create mode 100644 erlang/recipes/default.rb
Cookbook erlang version 0.8.2 successfully installed

So the third attempt worked, but that puts the cookbook in the chef-repo/ path, not in chef-repo/cookbooks/ which is where I assume it should land...

Commenting here in case someone else googles the same error: you need to configure the cookbook_path for knife. I added the following to $REPO_DIR/.chef/knife.rb:

# .chef/knife.rb
cookbook_path [File.join(File.dirname(__FILE__), "..", "cookbooks")]

^ Thanks for that.

Thank you urbanautomaton!