Unescape values correctly

lib/dotenv/parser.rb

@@ -1,5 +1,6 @@
 require "dotenv/substitutions/variable"
 require "dotenv/substitutions/command" if RUBY_VERSION > "1.8.7"
+require "dotenv/substitutions/unescape"
 
 module Dotenv
   class FormatError < SyntaxError; end
@@ -8,8 +9,11 @@ class FormatError < SyntaxError; end
   # and stored in the Environment. It allows for variable substitutions and
   # exporting of variables.
   class Parser
-    @substitutions =
-      Substitutions.constants.map { |const| Substitutions.const_get(const) }
+    @substitutions = [
+      Substitutions::Variable,
+      Substitutions.const_defined?(:Command) ? Substitutions::Command : nil,
+      Substitutions::Unescape
+    ].compact
 
     LINE = /
       \A
@@ -79,7 +83,7 @@ def parse_value(value)
     end
 
     def unescape_characters(value)
-      value.gsub(/\\([^$])/, '\1')
+      value.gsub(/([^\\]|^)\\([^$\\])/, '\1\2')
     end
 
     def expand_newlines(value)

lib/dotenv/substitutions/unescape.rb

@@ -0,0 +1,18 @@
+require "English"
+
+module Dotenv
+  module Substitutions
+    # Substitute "\$" to "$"
+    #
+    module Unescape
+      class << self
+        ESCAPED_DOLLARS = /\\\$/
+        ESCAPED_BACKSLASHES =  /\\\\/
+
+        def call(value, _env)
+          value.gsub(ESCAPED_DOLLARS, '$').gsub(ESCAPED_BACKSLASHES, "\\")
+        end
+      end
+    end
+  end
+end

lib/dotenv/substitutions/variable.rb

@@ -10,21 +10,21 @@ module Substitutions
     module Variable
       class << self
         VARIABLE = /
-          (\\)?        # is it escaped with a backslash?
-          (\$)         # literal $
-          \{?          # allow brace wrapping
-          ([A-Z0-9_]+) # match the variable
-          \}?          # closing brace
+          (([^\\]|^)\\)?        # is it escaped with a backslash but not escaped backslash?
+          (\$)                  # literal $
+          \{?                   # allow brace wrapping
+          ([A-Z0-9_]+)          # match the variable
+          \}?                   # closing brace
         /xi
 
         def call(value, env)
           value.gsub(VARIABLE) do |variable|
             match = $LAST_MATCH_INFO
 
-            if match[1] == '\\'
-              variable[1..-1]
+            if match[1]
+              match[2] + variable[match[1].size .. -1]
             else
-              env.fetch(match[3]) { ENV[match[3]] }
+              env.fetch(match[4]) { ENV[match[4]] }
             end
           end
         end

spec/dotenv/parser_spec.rb

@@ -64,6 +64,13 @@ def env(string)
       .to eql("FOO" => "test", "BAR" => "foo${FOO} test")
   end
 
+  it "unescapes correctly" do
+    expect(env("FOO=\"foo\\$.test\"")).to eql("FOO" => "foo$.test")
+    expect(env("FOO=\"foo\\$\"")).to eql("FOO" => "foo$")
+    expect(env("FOO=\"foo\\$.\"")).to eql("FOO" => "foo$.")
+    expect(env("BAR=bar\nFOO=\"foo\\\\$BAR\"")).to eql("BAR" => "bar", "FOO" => "foo\\bar")
+  end
+
   it "parses yaml style options" do
     expect(env("OPTION_A: 1")).to eql("OPTION_A" => "1")
   end