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README.md

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+# dcmerge
+
+[![Build Status](https://drone.cryptic.systems/api/badges/volker.raschek/dcmerge/status.svg)](https://drone.cryptic.systems/volker.raschek/dcmerge)
+[![Docker Pulls](https://img.shields.io/docker/pulls/volkerraschek/dcmerge)](https://hub.docker.com/r/volkerraschek/dcmerge)
+
+`dcmerge` is a small program to merge docker-compose files from multiple
+sources. It is available via RPM and docker.
+
+The dynamic pattern of a docker-compose file, that for example `environments`
+can be specified as a string slice or a list of objects is currently not
+supported. `dcmerge` expect a strict pattern layout. The `environments`, `ports`
+and `volumes` must be declared as a slice of strings.
+
+Dockercompose file can be read-in from different sources. Currently are the
+following sources supported:
+
+- File
+- HTTP/HTTPS
+
+Furthermore, `dcmerge` support different ways to merge multiple docker-compose
+files.
+
+- The default merge, add missing secrets, services, networks and volumes.
+- The existing-win merge, add and protect existing attributes.
+- The last-win merge, add or overwrite existing attributes.
+
+## default
+
+Merge only missing secrets, services, networks and volumes without respecting
+their attributes. For example, when the service `app` is already declared, it is
+not possible to add the service `app` twice. The second service will be
+completely skipped.
+
+```yaml
+---
+# cat ~/docker-compose-A.yaml
+services:
+  app:
+    environments:
+    - CLIENT_SECRET=HelloWorld123
+    image: example.local/app/name:0.1.0
+---
+# cat ~/docker-compose-B.yaml
+services:
+  app:
+    image: app/name:2.3.0
+    volume:
+    - /etc/localtime:/etc/localtime
+    - /dev/urandom:/etc/urandom
+  db:
+    image: postgres
+    volume:
+    - /etc/localtime:/etc/localtime
+    - /dev/urandom:/etc/urandom
+---
+# dcmerge ~/docker-compose-A.yaml ~/docker-compose-B.yaml
+services:
+  app:
+    environments:
+    - CLIENT_SECRET=HelloWorld123
+    image: example.local/app/name:0.1.0
+  db:
+    image: postgres
+    volume:
+    - /etc/localtime:/etc/localtime
+    - /dev/urandom:/etc/urandom
+```
+
+## existing-win
+
+The existing-win merge protects existing attributes. For example there are two
+different docker-compose files, but booth has the same environment variable
+`CLIENT_SECRET` defined with different values. The first declaration of the
+attribute wins and is for overwriting protected.
+
+```yaml
+---
+# cat ~/docker-compose-A.yaml
+services:
+  app:
+    environments:
+    - CLIENT_SECRET=HelloWorld123
+    image: example.local/app/name:0.1.0
+---
+# cat ~/docker-compose-B.yaml
+services:
+  app:
+    environments:
+    - CLIENT_SECRET=FooBar123
+    image: example.local/app/name:0.1.0
+---
+# dcmerge --existing-win ~/docker-compose-A.yaml ~/docker-compose-B.yaml
+services:
+  app:
+    environments:
+    - CLIENT_SECRET=HelloWorld123
+    image: example.local/app/name:0.1.0
+```
+
+## last-win
+
+The last-win merge overwrite recursive existing attributes. For example there
+are two different docker-compose files, but booth has the same environment
+variable `CLIENT_SECRET` defined with different values. The last passed
+docker-compose file which contains this environment wins.
+
+```yaml
+---
+# cat ~/docker-compose-A.yaml
+services:
+  app:
+    environments:
+    - CLIENT_SECRET=HelloWorld123
+    image: example.local/app/name:0.1.0
+---
+# cat ~/docker-compose-B.yaml
+services:
+  app:
+    environments:
+    - CLIENT_SECRET=FooBar123
+    image: example.local/app/name:0.1.0
+---
+# dcmerge --last-win ~/docker-compose-A.yaml ~/docker-compose-B.yaml
+services:
+  app:
+    environments:
+    - CLIENT_SECRET=FooBar123
+    image: example.local/app/name:0.1.0
+```