Adding env datasource

Signed-off-by: Dave Henderson <dhenderson@gmail.com>

1 files changed, 30 insertions, 0 deletions

diff --git a/docs/content/datasources.md b/docs/content/datasources.md
index e80744ee..f31128ae 100644
--- a/docs/content/datasources.md
+++ b/docs/content/datasources.md
@@ -42,6 +42,7 @@ Gomplate supports a number of datasources, each specified with a particular URL
 | [AWS Systems Manager Parameter Store](#using-aws-smp-datasources) | `aws+smp` | [AWS Systems Manager Parameter Store][AWS SMP] is a hierarchically-organized key/value store which allows storage of text, lists, or encrypted secrets for retrieval by AWS resources |
 | [BoltDB](#using-boltdb-datasources) | `boltdb` | [BoltDB][] is a simple local key/value store used by many Go tools |
 | [Consul](#using-consul-datasources) | `consul`, `consul+http`, `consul+https` | [HashiCorp Consul][] provides (among many other features) a key/value store |
+| [Environment](#using-env-datasources) | `env` | Environment variables can be used as datasources - useful for testing |
 | [File](#using-file-datasources) | `file` | Files can be read in any of the [supported formats](#supported-formats), including by piping through standard input (`Stdin`) |
 | [HTTP](#using-http-datasources) | `http`, `https` | Data can be sourced from HTTP/HTTPS sites in many different formats. Arbitrary HTTP headers can be set with the [`--datasource-header`/`-H`][] flag |
 | [Stdin](#using-stdin-datasources) | `stdin` | A special case of the `file` datasource; allows piping through standard input (`Stdin`) |
@@ -226,6 +227,35 @@ $ gomplate -d consul=consul:///foo -i '{{(datasource "consul" "bar/baz")}}'
 value for foo/bar/baz key
 ```
 
+## Using `env` datasources
+
+The `env` datasource type provides access to environment variables. This can be useful for rendering templates that would normally use a different sort of datasource, in test and development scenarios.
+
+No hierarchy or directory semantics are currently supported.
+
+**Note:** Variable names are _case-sensitive!_
+
+### URL Considerations
+
+The _scheme_ and either the _path_ or the _opaque_ part are used, and the _query_ component can be used to [override the MIME type](#overriding-mime-types).
+
+- the _scheme_ must be `env`
+- one of the _path_ or _opaque_ component is required, and is interpreted as the environment variable's name. Leading `/` characters are stripped from the _path_.
+
+### Examples
+
+```console
+$ gomplate -d user=env:USER -i 'Hello {{ include "user" }}!'
+Hello hairyhenderson!
+
+$ gomplate -d homedir=env:///HOME -i '{{ files.IsDir (ds "homedir") }}'
+true
+
+$ export foo='{"one":1, "two":2}'
+$ gomplate -d foo=env:/foo?type=application/json -i '{{ (ds "foo").two }}'
+2
+```
+
 ## Using `file` datasources
 
 The `file` datasource type provides access to files in any of the [supported formats](#mime-types). [Directory datasource](#directory-datasources) semantics are supported.