Version Matrix

CEM - Code Examples Manager Scala CI

Code example manager (CEM) is a software tool which manage your code examples and provide publish mechanisms to (as gists) or (as snippets).

Current Code example manager (CEM) implementation is just a command line tool which compare locally available examples with already published ones in order to find what it should do (add, update, do nothing).

All my code examples (my programming knowledge base) are now shared using this tool, you can take a look to my public gists overview on github to illustrate the publishing work achieved by CEM.

The origin of this tool comes from this talk originally presented at AlpesCraft 2019.

Why ?

Code examples are very important, each example is most of the time designed to focus on a particular feature/characteristic of a programming language, a library or a framework. They help us to quickly test, experiment and remember how bigger project or at least some parts of them are working.

See the rules for good code examples for more information.

Managing hundreds of published code example files as gists (github) and/or snippets (gitlab) is really not easy and time-consuming, in particular if you want to keep them up to date.

That's why I've decided to automate their management. The first iteration was script based, (and so shared as a gist) but with the increase of complexity , a dedicated project became necessary, and so code-examples-manager was born. After a huge refactoring, which has introduced mustache templating, better configuration management, multiple publishing targets, gitlab snippets support, code-examples-manager is now mature. I'm using it at least once each week.

Start small, make it works quickly, and then refactor !

A lot of thanks to Li Haoyi for his wonderful work on ammonite which is probably the best solution for code examples and scripting in scala.

Quick start

No particular prerequisites, just a Java >=8 JVM available, and it will run on your Linux, Windows or MacOSX

Instructions example with publishing configuration :

  • Install the coursier from @alxarchambault to automate the download/update/start of code-examples-manager directly from maven repositories
  • Customize your configuration (see below for token configuration)
    export CEM_SEARCH_ROOTS="/home/myuser/myexamples"
    export CEM_SEARCH_GLOB="**/*.{sc,sh,*.md,*.jsh}"
    export CEM_GITHUB_TOKEN="xxxxx"
  • Create an example file in /home/myuser/myexamples such as
    // summary : my markdown cheat sheet
    // keywords : markdown, hello, example 
    // publish : gist
    // authors : someone, someonelse
    // id : d27245fc-22fb-4c9e-9809-feb0826400e7
    # Hello world !
    this is just an example
  • Run the following command from your terminal (cs is the coursier CLI command):
    cs launch fr.janalyse::code-examples-manager:1.0.9
    • you can even use cs launch fr.janalyse::code-examples-manager:latest.release to always use the latest release
    • current release is :
  • Check the command output to get the overview URL

Code examples

In order to be published your code examples must come with a description header inserted using single line comments. You must provide a unique identifier (UUID) to each of your example, as well as a summary and publish keywords which define remote destinations.

Example for languages using // for line comments :

// summary : Simplest scalatest test framework usage.
// keywords : scala, scalatest, pi, @testable
// publish : gist, snippet
// authors : David Crosson
// license : Apache
// id : d24d8cb3-45c0-4d88-b033-7fae2325607b
// execution : scala ammonite script ( - run as follow 'amm'
import $ivy.`org.scalatest::scalatest:3.2.0`
import org.scalatest._,matchers.should.Matchers._
math.Pi shouldBe 3.14d +- 0.01d

Request keys in description header are the following :

  • summary : example one line summary.
  • keywords : keywords describing your code features (comma separated).
  • publish : publish destination keywords (comma separated)
    • the default configuration file provide those activation keywords :
      • gist : for
      • snippet : for
  • authors : code example authors list (comma separated).
  • license : the example license.
  • id : UUID for this code example. Generated using such commands :
    • this ammonite scala script.
    • This linux command (comes from package named uuid-runtime at least on debian based linux) :
    • This ammonite oneliner :
      amm -c 'println(java.util.UUID.randomUUID.toString)'
    • This python oneliner :
      python -c "import uuid, sys;sys.stdout.write(str(uuid.uuid4()))"
  • execution : how to execute the example, execution runtime release constraints, ...

CEM operations

Code examples manager operations :

  • It reads its configuration
  • It searches for code examples from the given directories roots
    • Only files with given extensions are selected (the given glob)
    • Selects code examples if and only if they contain a unique identifier (UUID)
  • It publishes or updates remote code examples to remote destinations
    • the code example publish scope (publish keyword) select target destinations
      • comma separated publish activation keyword (activation-keyword parameter in configuration)
    • It adds or updates a global overview of all published examples for a given destination
      • this summary has its own UUID defined in the configuration file


The configuration relies on configuration files, a default one named reference.conf is provided. This default configuration file defines default values and default behaviors and allow a simple configuration way based on environment variables which override default values.

Simplified configuration

env or property name description
CEM_SEARCH_ROOTS examples search roots
CEM_SEARCH_GLOB examples files globs
CEM_GITLAB_TOKEN gitlab authentication token for snippets API access
CEM_GITHUB_TOKEN github authentication token for gists API access, see below for how to get this token
CEM_EXAMPLES_OVERVIEW_UUID the fixed UUID for the overview GIST which list all examples, default value is cafacafe-cafecafe
CEM_CONFIG_FILE your custom advanced configuration file (optional, see next section for more information)

Configuration examples :

export CEM_SEARCH_ROOTS="/tmp/someplace,/tmp/someotherplace"
export CEM_SEARCH_GLOB="**/*.{sc,sh,*.md,*.jsh}"
export CEM_GITHUB_TOKEN="fada-fada-fada-fada"

Advanced configuration

Take a look to the configuration file for more information about advanced configuration.

Once CEM installed you can modify the provided conf/application.conf file (whose content is by default the same as the default reference.conf file), remember that any unset parameter in application.conf will default to the value defined in reference.conf.

Note : It is also possible to provide a custom configuration file through the config.file java property or the CEM_CONFIG_FILE environment variable.

Authentication tokens

Gitlab authentication token configuration

Get an access token from gitlab :

  • Go to your user settings
    • Select Access tokens
      • Add a Personal access token
        • Enable scopes : api and read_user
  • setup your CEM_GITLAB_TOKEN environment variable or token parameter in your configuration file with the generated token
  • Keep it carefully as it is not possible to retrieve it later.
  • And of course KEEP IT SECURE

Github authentication token configuration

Get an access token from :

  • Got to your user settings
    • Select Developer settings
      • Select Personal access tokens
        • Then generate new token
          • Enable scopes : gist and read:user
  • setup your CEM_GITHUB_TOKEN environment variable or token parameter in your configuration file with the generated token, the value shown within curl json response
  • Keep it carefully as it is not possible to retrieve it later.
  • And of course KEEP IT SECURE