Replace a HTML tag (<terraform-docs>) with markdown documentation via terraform-docs.

replace-terraform-docs.rb

#!/usr/bin/env ruby
require 'optparse'

options = { output: STDOUT }
OptionParser.new do |opts|
  opts.banner = 'Usage: replace.rb <source-file.md> [options]'

  opts.on("-o", "--output=OUTPUT", "The file path to output results from (default: STDOUT)") do |v|
    options[:output] = File.open(options[:output], 'w')
  end

  opts.on("-m", "--module-path=PATH", "The path to a module to generate documentation for (default: dirname of source file)") do |v|
    options[:module_path] = v
  end

  opts.on("-O", "--overwrite", "Whether to overwrite the source file (default: false)") do |v|
    options[:overwrite] = true
  end

  opts.on("-h", "--help", "Show this help message") do
    puts opts
    exit
  end
end.parse!

unless system('which terraform-docs > /dev/null 2>&1')
  warn 'Please install terraform-docs and ensure it is on your path.'
  exit 1
end

source = ARGV[0] || '-'
if source == '-'
  warn 'Reading STDIN...'
  options[:module_path] ||= '.'
  original = STDIN.read
else
  options[:module_path] ||= File.dirname(source)
  original = File.read(source)
end

output = options[:output]
if options[:overwrite] && source != '-'
  output = File.open(source, 'w')
end

replace_tag_regexp = %r{
  <terraform-docs/>|                  # Place holder tag.
  <terraform-docs>.*</terraform-docs> # Open and closing tags including children/text.
}mx
terraform_docs_output = `terraform-docs md #{options[:module_path]}`
wrapped_markdown = "<terraform-docs>\n#{terraform_docs_output}\n</terraform-docs>"
output.puts original.gsub(replace_tag_regexp, wrapped_markdown)