DIP_CURRENT_USER added (#168)

* Expose current user UID as an environment variable

* Update README

* Add an example of using the current user in a docker container

* Change up the example

README.md

@@ -222,6 +222,27 @@ dip run bash -c pwd
 
 returned is `/app/sub-project-dir`.
 
+#### $DIP_CURRENT_USER
+
+Exposes the current user ID (UID). It is useful when you need to run a container with the same user as the host machine. For example:
+
+```yml
+# dip.yml (1)
+environment:
+  UID: ${DIP_CURRENT_USER}
+```
+
+```yml
+# docker-compose.yml (2)
+services:
+  app:
+    image: ruby
+    user: ${UID:-1000}
+```
+
+The container will run using the same user ID as your host machine.
+
+
 ### dip run
 
 Run commands defined within the `interaction` section of dip.yml

lib/dip/environment.rb

@@ -5,7 +5,7 @@
 module Dip
   class Environment
     VAR_REGEX = /\$\{?(?<var_name>[a-zA-Z_][a-zA-Z0-9_]*)\}?/.freeze
-    SPECIAL_VARS = %i[os work_dir_rel_path].freeze
+    SPECIAL_VARS = %i[os work_dir_rel_path current_user].freeze
 
     attr_reader :vars
 
@@ -63,5 +63,9 @@ def find_os
     def find_work_dir_rel_path
       @find_work_dir_rel_path ||= Pathname.getwd.relative_path_from(Dip.config.file_path.parent).to_s
     end
+
+    def find_current_user
+      @find_current_user ||= Process.uid
+    end
   end
 end