parse erb templates from command line (standalone, cli, json)

README.md

Goal

• provide cli command to render erb template
• template params (bindings) to be provided using json format
• use inputs from file (template.erb, params.json)
• use inputs from cli options / parameters
• render output to stdout OR to file

Why ?

• helps creating build & deploy pipelines

Usage

Help:

$ ruby json_erb_render.rb --help

Examples:

$ ruby json_erb_render.rb -i ./example/foo.erb -d ./example/config.json

$ ruby json_erb_render.rb -i ./example/foo.erb -d ./example/config.json -o ./out.txt

$ ruby json_erb_render.rb -t "FOO_BAR=<%= @config['foo'] %>" -d ./example/config.json

$ ruby json_erb_render.rb -t "FOO_BAR=<%= @config['foo'] %>" -p "{"foo":"bar"}"

$ ruby json_erb_render.rb -t "FOO_BAR=<%= @config['foo'] %>" -p "{"foo":"bar"}" -o ./out.txt

Docker

• no need to install ruby

• just run against official ruby image

  $ docker run --rm -it
  -e "$$PATH=$(PATH)"
  --volume "$(PWD)":"/src" -w /src
  ruby:2.3
  ruby /src/example/json_erb_render.rb -i /src/example/foo.erb -d /src/example/config.json

Limitations

• no proper validations implemented, ruby will throw its exceptions if sth. is wrong

json_erb_render.rb

#!/usr/bin/env ruby

# usage:
# ruby json_erb_render.rb OPTIONS

# help:
# ruby json_erb_render.rb --help

# examples:
# ruby json_erb_render.rb -i ./example/foo.erb -d ./example/config.json
# ruby json_erb_render.rb -i ./example/foo.erb -d ./example/config.json -o ./out.txt
# ruby json_erb_render.rb -t "FOO_BAR=<%= @config['foo']['bar'] %>" -d ./example/config.json
# ruby json_erb_render.rb -t "FOO_BAR=<%= @config['foo']['bar'] %>" -p "{\"foo\":\"bar\"}"
# ruby json_erb_render.rb -t "FOO_BAR=<%= @config['foo']['bar'] %>" -p "{\"foo\":\"bar\"}" -o ./out.txt

require 'erb'
require 'json'
require 'pathname'
require 'optparse'
require 'ostruct'

options = OpenStruct.new
OptionParser.new do |opt|
  opt.on('-i', '--input_file TEMPLATE_FILE', 'The template file being processed. e.g.: ./example/foo.erb') { |o| options['input_file'] = o }
  opt.on('-t', '--template_text TEMPLATE_TEXT', 'The template text being processed. e.g.: "FOO_BAR=<%= @config[\'foo\'][\'bar\'] %>"') { |o| options['template_text'] = o }
  opt.on('-d', '--data_file DATA_FILE', 'The config file (json) being processed. e.g.: ./example/config.json') { |o| options['data_file'] = o }
  opt.on('-p', '--template_params TEMPLATE_PARAMS', 'The template params (json) being processed. e.g.: -p "{\"foo\":\"bar\"}"') { |o| options['template_params'] = o }
  opt.on('-o', '--output_file SINK_FILE', 'The output file. if not specified, output gets rendered to stdout. e.g.: ./out.txt') { |o| options['output_file'] = o }
end.parse!




data_file = options['data_file']
data_text = options['template_params']

template_file = options['input_file']
template_text = options['template_text']

output_file = options['output_file']

class TemplateBuilder
  attr_accessor :config

  def initialize(config)
    @config = config
  end

  # Expose private binding() method.
  def get_binding
    binding()
  end

end

if template_file ==nil
  template=template_text
else
  template=File.read(template_file)
end

if data_file ==nil
  params=JSON.parse(data_text)
else
  params=JSON.parse(File.read(data_file))
end


renderer = ERB.new(template)
builder = TemplateBuilder.new(params)
result = renderer.result(builder.get_binding)

if output_file==nil
  puts result
else
  output = File.new(output_file, 'w')
  output.puts(result)
  output.close
end

This is fantastic. Could you turn this into a git repo so pull requests could be made? I'd like to add YAML support and some other functionality.

Would have been nice if you included the example foo.erb and config.json as well. Can you add those?