Inject system environment variables to configuration settings in platformio.ini // Resolve #792

HISTORY.rst

@@ -11,6 +11,9 @@ PlatformIO 3.0
   Your devices are always with you!
 * `PIO Account <http://docs.platformio.org/en/latest/userguide/account/index.html>`__
   for extra professional features from `PlatformIO Plus <https://pioplus.com>`__
+* Inject system environment variables to configuration settings in
+  `Project Configuration File "platformio.ini" <http://docs.platformio.org/en/stable/projectconf.html>`__
+  (`issue #792 <https://github.com/platformio/platformio/issues/792>`_)
 * Changed default exit combination for Device Monitor from ``Ctrl+]`` to ``Ctrl+C``
 * Improved detecting of ARM mbed media disk for uploading
 * Improved Project Generator for CLion IDE when source folder contains nested items

docs/projectconf.rst

@@ -48,10 +48,13 @@ Each variable should have a next format: ``${<section>.<option>}``, where
 ``<section>`` is a value from ``[<section>]`` group, and ``<option>`` is a
 first item from pair ``<option> = value``.
 
+You can inject environment variable using ``env`` as a ``section``. For example,
+``${env.HOME}``, etc.
+
 * Variable can be applied only for the option's value
 * Multiple variables are allowed
-* The ``platformio`` section is reserved and could not be used as custom
-  section. Some good section names might be ``common`` or ``global``.
+* The ``platformio`` and ``env`` sections are reserved and could not be used
+  as custom section. Some good section names might be ``common`` or ``global``.
 
 Example:
 
@@ -68,6 +71,7 @@ Example:
     board = uno
     build_flags = ${common.build_flags}
     lib_deps = ${common.lib_deps_builtin}, ${common.lib_deps_external}
+    lib_extra_dirs = ${env.HOME}/arduino/libs
 
     [env:nodemcuv2]
     platform = espressif8266

platformio/util.py

@@ -59,7 +59,10 @@ class ProjectConfig(ConfigParser):
         return self.VARTPL_RE.sub(self._re_sub_handler, value)
 
     def _re_sub_handler(self, match):
-        return self.get(match.group(1), match.group(2))
+        section, option = match.group(1), match.group(2)
+        if section == "env" and not self.has_section(section):
+            return os.getenv(option)
+        return self.get(section, option)
 
 
 class AsyncPipe(Thread):