feature: Initial implementation

.circleci/config.yml

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+version: 2
+
+# Re-usable blocks to reduce boilerplate in job definitions.
+references:
+  default_machine_job: &default_machine_job
+    machine: true
+    working_directory: ~/workdir
+
+  set_version_env_variable: &set_version_env_variable
+    run:
+      name: Define Environment Variable VERSION_NUMBER and ENV at Runtime
+      command: |
+        echo export VERSION_NUMBER=$(cat ~/workdir/.version) >> $BASH_ENV
+        source $BASH_ENV
+        echo $VERSION_NUMBER
+
+  compile_crystal: &compile_crystal
+    run:
+      name: Get version
+      command: |
+        make clean buildStatic
+
+jobs:
+  checkout_and_version:
+    docker:
+      - image: codacy/git-version:latest
+    working_directory: ~/workdir
+    steps:
+      - checkout
+      - run:
+          name: Set version
+          command: /bin/git-version > .version
+      - run:
+          name: Current version
+          command: cat .version
+      - persist_to_workspace:
+          root: ~/
+          paths:
+            - workdir
+
+  compile:
+    <<: *default_machine_job
+    steps:
+      - run:
+          name: Compile
+          command: make clean buildStatic
+      - persist_to_workspace:
+          root: ~/
+          paths:
+            - workdir/*
+      - store_artifacts:
+          path: bin
+
+  publish-github-release:
+    docker:
+      - image: circleci/golang:1.8
+    steps:
+      - attach_workspace:
+          at: ./artifacts
+      - run:
+          name: "Publish Release on GitHub"
+          command: |
+            go get github.com/tcnksm/ghr
+            VERSION=$(cat .version)
+            ghr -t ${GITHUB_TOKEN} -u ${CIRCLE_PROJECT_USERNAME} -r ${CIRCLE_PROJECT_REPONAME} -c ${CIRCLE_SHA1} -delete ${VERSION} ./artifacts/
+
+  tag-version:
+    <<: *default_machine_job
+    steps:
+      - attach_workspace:
+          at: ~/
+      - add_ssh_keys:
+          fingerprints:
+            - "df:83:d7:c7:d5:79:06:c2:3b:d1:fd:e2:a3:d1:12:c5"
+      - deploy:
+          name: Tag git repository
+          command: git tag $(cat .version) && git push --tags
+
+workflows:
+  version: 2
+  publish:
+    jobs:
+      - checkout_and_version
+      - compile:
+          requires:
+            - checkout_and_version
+      - publish-github-release:
+          requires:
+            - compile
+          filters:
+            branches:
+              only:
+              - master
+          context: CodacyAWS
+      - tag-version:
+          requires:
+            - publish-github-release
+          filters:
+            branches:
+              only:
+                - master
+          context: CodacyAWS

.gitignore

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+bin

Makefile

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+CRYSTAL=/usr/bin/crystal
+CRYSTAL_FLAGS=--release
+
+all: fmt build
+
+.PHONY: fmt
+fmt: ## format the crystal sources
+	$(CRYSTAL) tool format
+
+.PHONY: docker
+build: fmt ## compiles from crystal sources
+	mkdir -p bin
+	$(CRYSTAL) build $(CRYSTAL_FLAGS) src/env2props.cr -o bin/env2props
+
+.PHONY: clean
+clean: ## clean target directories
+	rm -rf bin
+
+buildStatic: ## compiles from crystal sources into static binary
+	docker run --rm -it -v $(PWD):/app -w /app durosoft/crystal-alpine:latest crystal build src/env2props.cr -o bin/env2props --release --static --no-debug
+
+.PHONY: help
+help:
+	@echo "make help"
+	@echo "\n"
+	@grep -E '^[a-zA-Z_/%\-]+:.*?## .*$$' $(MAKEFILE_LIST) | sort | awk 'BEGIN {FS = ":.*?## "}; {printf "\033[36m%-30s\033[0m %s\n", $$1, $$2}'
+	@echo "\n"

Readme.md

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+
+# ENV2PROPS
+
+This is a tool to transform your environment variables into the java Properties format intended to be passed from the command line.
+
+e.g.:
+
+```
+$ env
+LC_PAPER=en_US.UTF-8
+LC_MONETARY=en_US.UTF-8
+LANG=en_US.UTF-8
+
+$ env2props
+-Dlc.paper="en_US.UTF-8" -Dlc.monetary="en_US.UTF-8" -Dlang="en_US.UTF-8"
+```
+
+Under the option `-p` or `--prefix` you can pass a matching prefix for the environment variables.
+
+e.g.:
+
+```
+$ env
+LC_PAPER=en_US.UTF-8
+LC_MONETARY=en_US.UTF-8
+LANG=en_US.UTF-8
+
+$ env2props -p LC_
+-Dpaper="en_US.UTF-8" -Dmonetary="en_US.UTF-8"
+```
+
+The output is provided on standard output and without any additional new-line, as it is intended to be used in-line within java command execution.
+
+## Conventions
+
+Each environment variable is transformed as follows:
+
+ - remove the trailing prefix (if specified)
+ - down case the entire string
+ - trasform all the `_` characters into `.`
+
+## Usage
+
+After making the binary executable and available on the `PATh`(should work out-of-the-box on any linux machine).
+You can use this tool in-line while launching java applications e.g.:
+
+```
+sh -c "java $(env2props) -jar <application>.jar"
+```
+
+## Rationale
+
+According to the [Twelve-factor App](https://12factor.net/config) the configuration should be passed to the applications via environment variables.
+
+The "de-facto" standard for configuration in Scala application is [Typesafe Config](https://github.com/lightbend/config) and env variables are a [supported fallback](https://github.com/lightbend/config#optional-system-or-env-variable-overrides); still it is not possible to override *virtually* any configuration of our application if not properly encoded the binding accordingly.
+
+Although [Typesafe Config](https://github.com/lightbend/config#overview) offers a first class integration with Java system properties:
+
+> users can override the config with Java system properties
+
+This makes it easy to bridge the gap and by having a standard way to convert environment variables into Java system properties make it possible to fully comply with [Twelve-factor App](https://12factor.net/config).
+
+## Compile
+
+You need to have the crystal compiler available in your classpath to succesfully build this utility, otherwise you can compile it statically using a docker image using `make buildStatic`.
+
+## What is Codacy
+
+[Codacy](https://www.codacy.com/) is an Automated Code Review Tool that monitors your technical debt, helps you improve your code quality, teaches best practices to your developers, and helps you save time in Code Reviews.
+
+### Among Codacy’s features
+
+- Identify new Static Analysis issues
+- Commit and Pull Request Analysis with GitHub, BitBucket/Stash, GitLab (and also direct git repositories)
+- Auto-comments on Commits and Pull Requests
+- Integrations with Slack, HipChat, Jira, YouTrack
+- Track issues in Code Style, Security, Error Proneness, Performance, Unused Code and other categories
+
+Codacy also helps keep track of Code Coverage, Code Duplication, and Code Complexity.
+
+Codacy supports PHP, Python, Ruby, Java, JavaScript, and Scala, among others.
+
+## Free for Open Source
+
+Codacy is free for Open Source projects.
+
+## License
+
+git-version is available under the Apache 2 license. See the LICENSE file for more info.

src/env2props.cr

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+require "option_parser"
+
+prefix = ""
+
+OptionParser.parse! do |parser|
+  parser.banner = "Usage: env2prop [arguments]"
+  parser.on("-p PREFIX", "--prefix=PREFIX", "Transform only the ENV variables that have the provided prefix") { |p| prefix = p }
+  parser.on("-h", "--help", "Show this help") { puts parser }
+  parser.invalid_option do |flag|
+    STDERR.puts "ERROR: #{flag} is not a valid option."
+    STDERR.puts parser
+    exit(1)
+  end
+end
+
+first = true
+
+props = String.build do |props|
+  ENV.each do |k, v|
+    if !k.starts_with?(prefix)
+      next
+    end
+
+    key = k
+      .lchop(prefix)
+      .downcase       # all downcase
+      .gsub("_", ".") # all underscores to dots
+
+    # given https://docs.oracle.com/javase/8/docs/api/java/util/Properties.html#load-java.io.InputStream-
+    encoding = "ISO8859-1"
+    str = String.new(bytes: v.encode(encoding), encoding: encoding)
+
+    str = str.dump
+
+    if (key.size > 1) || (key.size == 1 && key[0].alphanumeric?)
+      if first
+        first = false
+      else
+        props << " "
+      end
+
+      props << "-D#{key}=#{str}"
+    end
+  end
+end
+
+STDOUT.set_encoding("UTF-8")
+STDOUT.print props