Support POSIX parameter expansion

README.rst

@@ -84,6 +84,17 @@ ignored.
     # I am a comment and that is OK
     FOO="BAR"
 
+``.env`` can interpolate variables using POSIX variable expansion, variables
+are replaced from the environment first or from other values in the ``.env``
+file if the variable is not present in the environment.
+
+.. code:: shell
+
+    CONFIG_PATH=${HOME}/.config/foo
+    DOMAIN=example.org
+    EMAIL=admin@${DOMAIN}
+
+
 Django
 ------
 
@@ -209,6 +220,13 @@ us a pull request.
 This project is currently maintained by `Saurabh Kumar <https://saurabh-kumar.com>`__ and
 would not have been possible without the support of these `awesome people <https://github.com/theskumar/python-dotenv/graphs/contributors>`__.
 
+Executing the tests:
+
+::
+
+    $ flake8
+    $ pytest
+
 Changelog
 =========
 
@@ -217,6 +235,7 @@ dev
 - Drop support for Python 2.6
 - Handle escaped charaters and newlines in quoted values. (Thanks `@iameugenejo`_)
 - Remove any spaces around unquoted key/value. (Thanks `@paulochf`_)
+- Added POSIX variable expansion.
 
 0.5.1
 ----------

dotenv/cli.py

@@ -2,7 +2,7 @@
 
 import click
 
-from .main import get_key, parse_dotenv, set_key, unset_key
+from .main import get_key, dotenv_values, set_key, unset_key
 
 
 @click.group()
@@ -35,7 +35,7 @@ def cli(ctx, file, quote):
 def list(ctx):
     '''Display all the stored key/value.'''
     file = ctx.obj['FILE']
-    dotenv_as_dict = parse_dotenv(file)
+    dotenv_as_dict = dotenv_values(file)
     for k, v in dotenv_as_dict:
         click.echo('%s="%s"' % (k, v))
 

dotenv/main.py

@@ -5,9 +5,11 @@
 import os
 import sys
 import warnings
+import re
 from collections import OrderedDict
 
 __escape_decoder = codecs.getdecoder('unicode_escape')
+__posix_variable = re.compile('\$\{[^\}]*\}')
 
 
 def decode_escaped(escaped):
@@ -21,7 +23,7 @@ def load_dotenv(dotenv_path):
     if not os.path.exists(dotenv_path):
         warnings.warn("Not loading %s - it doesn't exist." % dotenv_path)
         return None
-    for k, v in parse_dotenv(dotenv_path):
+    for k, v in dotenv_values(dotenv_path).items():
         os.environ.setdefault(k, v)
     return True
 
@@ -36,7 +38,7 @@ def get_key(dotenv_path, key_to_get):
     if not os.path.exists(dotenv_path):
         warnings.warn("can't read %s - it doesn't exist." % dotenv_path)
         return None
-    dotenv_as_dict = OrderedDict(parse_dotenv(dotenv_path))
+    dotenv_as_dict = dotenv_values(dotenv_path)
     if key_to_get in dotenv_as_dict:
         return dotenv_as_dict[key_to_get]
     else:
@@ -73,7 +75,7 @@ def unset_key(dotenv_path, key_to_unset, quote_mode="always"):
     if not os.path.exists(dotenv_path):
         warnings.warn("can't delete from %s - it doesn't exist." % dotenv_path)
         return None, key_to_unset
-    dotenv_as_dict = OrderedDict(parse_dotenv(dotenv_path))
+    dotenv_as_dict = dotenv_values(dotenv_path)
     if key_to_unset in dotenv_as_dict:
         dotenv_as_dict.pop(key_to_unset, None)
     else:
@@ -83,6 +85,12 @@ def unset_key(dotenv_path, key_to_unset, quote_mode="always"):
     return success, key_to_unset
 
 
+def dotenv_values(dotenv_path):
+    values = OrderedDict(parse_dotenv(dotenv_path))
+    values = resolve_nested_variables(values)
+    return values
+
+
 def parse_dotenv(dotenv_path):
     with open(dotenv_path) as f:
         for line in f:
@@ -103,6 +111,29 @@ def parse_dotenv(dotenv_path):
             yield k, v
 
 
+def resolve_nested_variables(values):
+    def _replacement(name):
+        """
+        get appropiate value for a variable name.
+        first search in environ, if not found,
+        then look into the dotenv variables
+        """
+        ret = os.getenv(name, values.get(name, ""))
+        return ret
+
+    def _re_sub_callback(match_object):
+        """
+        From a match object gets the variable name and returns
+        the correct replacement
+        """
+        return _replacement(match_object.group()[2:-1])
+
+    for k, v in values.items():
+        values[k] = __posix_variable.sub(_re_sub_callback, v)
+
+    return values
+
+
 def flatten_and_write(dotenv_path, dotenv_as_dict, quote_mode="always"):
     with open(dotenv_path, "w") as f:
         for k, v in dotenv_as_dict.items():

tests/test_cli.py

@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 from __future__ import unicode_literals
 
+from os import environ
 from os.path import dirname, join
 
 import dotenv
@@ -83,3 +84,37 @@ def test_default_path(cli):
         output = sh.dotenv('get', 'HELLO')
         assert output == 'HELLO="WORLD"\n'
         sh.rm(dotenv_path)
+
+
+def test_get_key_with_interpolation(cli):
+    with cli.isolated_filesystem():
+        sh.touch(dotenv_path)
+        dotenv.set_key(dotenv_path, 'HELLO', 'WORLD')
+        dotenv.set_key(dotenv_path, 'FOO', '${HELLO}')
+        dotenv.set_key(dotenv_path, 'BAR', 'CONCATENATED_${HELLO}_POSIX_VAR')
+
+        # test replace from variable in file
+        stored_value = dotenv.get_key(dotenv_path, 'FOO')
+        assert stored_value == 'WORLD'
+        stored_value = dotenv.get_key(dotenv_path, 'BAR')
+        assert stored_value == 'CONCATENATED_WORLD_POSIX_VAR'
+        # test replace from environ taking precedence over file
+        environ["HELLO"] = "TAKES_PRECEDENCE"
+        stored_value = dotenv.get_key(dotenv_path, 'FOO')
+        assert stored_value == "TAKES_PRECEDENCE"
+        sh.rm(dotenv_path)
+
+
+def test_get_key_with_interpolation_of_unset_variable(cli):
+    with cli.isolated_filesystem():
+        sh.touch(dotenv_path)
+        dotenv.set_key(dotenv_path, 'FOO', '${NOT_SET}')
+        # test unavailable replacement returns empty string
+        stored_value = dotenv.get_key(dotenv_path, 'FOO')
+        assert stored_value == ''
+        # unless present in environment
+        environ['NOT_SET'] = 'BAR'
+        stored_value = dotenv.get_key(dotenv_path, 'FOO')
+        assert stored_value == 'BAR'
+        del(environ['NOT_SET'])
+        sh.rm(dotenv_path)

tests/test_core.py

@@ -3,8 +3,9 @@
 import pytest
 import tempfile
 import warnings
+import sh
 
-from dotenv import load_dotenv, find_dotenv
+from dotenv import load_dotenv, find_dotenv, set_key
 
 
 def test_warns_if_file_does_not_exist():
@@ -55,3 +56,16 @@ def test_find_dotenv():
     with open(filename, 'w') as f:
         f.write("TEST=test\n")
     assert find_dotenv(usecwd=True) == filename
+
+
+def test_load_dotenv(cli):
+    dotenv_path = '.test_load_dotenv'
+    with cli.isolated_filesystem():
+        sh.touch(dotenv_path)
+        set_key(dotenv_path, 'DOTENV', 'WORKS')
+        assert 'DOTENV' not in os.environ
+        success = load_dotenv(dotenv_path)
+        assert success
+        assert 'DOTENV' in os.environ
+        assert os.environ['DOTENV'] == 'WORKS'
+        sh.rm(dotenv_path)