The withenv package installs the we executable. Here is the basic usage.
$ we --env foo.yml printenv
The YAML in foo.yml gets loaded and applied to the environment. If the value already exists in the environment, that value will be overwritten.
You can also use a directory of YAML files.
$ we --dir myenv printenv
The files will be applied to the environment in alphabetical order.
You can shorten the flags as well as mixing files and directories.
$ we -e foo.yml -d bar -e baz.yml printenv
Each flag will be applied in order from left to right.
You can use a hash or list of hashes in your YAML file. For example:
--- FOO: bar BAR: hello $FOO
It is not recommended to use a hash in this format because the order cannot be gauranteed, although, it will probably work just fine. If you need explicit ordering within your file, use a list of hashes.
--- - FOO: bar - BAR: hello $FOO
Here we see the $FOO variable is used within the value of $BAR.
Withenv also makes an effort to include environment files. Specifically, you can include a file that use the format:
Each line is parsed as an entry. This can be a typical shell script as lines that don’t start with export will be ignored. With that in mind, functions defined in the script will not be available.
Sometimes you want to replace a variable based on the result of a command. Say for example, you wanted to grab a value from a chef environment. We can use the knife and jq to grab the value and inject into our environment value.
--- - CHEF_ENV: dev - TOKEN: "`knife environment show $CHEF_ENV -Fj | jq --raw-output .default_attributes.token`"
The knife command will go to our chef server and grab the environment’s configuration and output it as JSON. This output is piped to the jq command where we are able to use JSONPath to grab the field value we need. The –raw-output will ensure we don’t have any quotes around the value.
We could then use this in a commmand.
$ we -e token.yml curl -H 'X-Auth-Token: $TOKEN' http://example.com/api/
Currently, withenv supports this dynamic substitution when the value starts and endswith a backtick.
Creating an Alias¶
Sometimes you’ll find that your environment is composed of a suite of details. Say for example, you were deploying an application via some script that uses environment variables to choose what region, cloud account and process to run.
$ we -d envs/apps/foo \ -e envs/acct/dev.yml \ -e envs/regions/us-east \ -E TAG=foo ./create-app-server
We can create an alias for this by creating an alias YAML file.
# myalias.yml --- - directory: envs/apps/foo - file: envs/acct/dev.yml - file: envs/regions/us-east - override: "TAG=foo"
We can then run our command with a shortened we command.
$ we -a myalias create-app-server
Withenv will look for a default alias file called .werc. The we command will look in the current directory and walk the filesystem until it finds a .werc file. If it finds a .werc, it will load it as an alias file prior to any command line arguments. If no .werc is found, we continues normally.
For example, lets say that you had a some projects for different clients. Each client provided credentials to a cloud account and you want to use the specific client when running commands.
The .werc might look like this:
# .werc --- - file: client.yml - file: ~/projects/clients/$CLIENT/creds.yml
The client.yml would add the $CLIENT env var. Now you could see what instances your client has running.
$ we ec2-describe-regions # or for rackspace $ we rack servers instance list