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+*~
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+* Steeplejack
+A generic scaffolding system.
+** About
+#+begin_quote
+A steeplejack is a craftsman who scales buildings, chimneys, and
+church steeples to carry out repairs or maintenance.
+
+Steeplejacks erect ladders on church spires, industrial chimneys,
+cooling towers, bell towers, clock towers, or any other high
+structure.
+#+end_quote
+
+Like a steeplejack, ~steeplejack~ is a diligent worker that can erect
+scaffolding for any project you need.
+** Usage
+~steeplejack~ can be taught how to erect scaffolding by setting the
+=STEEPLEJACK_DIR= (defaults to ~~/.steeplejack~)environment variable and
+putting template directories there.  A template directory contains a
+~_scaffold.yml~ and various ~.erb~ files.  ~_scaffold.yml~ should at least
+contain a =params= or =parameters= property.  It should be a list of
+property names.  Each parameter will be read when the scaffold is
+erected.  ~_scaffold.yml~ can also contain an =erb_options= parameter
+that, when present, is used to set the =trim_mode= for ERB.  See the [[https://docs.ruby-lang.org/en/master/ERB.html][ERB
+documentation]] for details.
+
+When the scaffold is erected, each ~.erb~ file in the scaffold’s
+directory is evaluated, and the output is written to the corresponding
+file in the target directory.  For example, let’s take a scaffold
+directory ~scaf~.  We will deploy it to ~targ~.  Let’s say that ~scaf~ has
+three files in it:
++ ~scaf/_scaffold.yml~
++ ~scaf/a.erb~
++ ~scaf/b.erb~
+Let’s also say that ~_scaffold.yml~ contains the text
+#+begin_src yaml
+  properties:
+    - foo
+    - bar
+#+end_src
+When deploying ~scaf~ to ~targ~, you will be prompted for =foo= and =bar=.
+Then ~scaf/a.erb~ and ~scaf/b.erb~ will be evaluated, and the results
+written to ~targ/a~ and ~targ/b~.
+** Configuration
+When ~steeplejack~ starts up, it loads ~$STEEPLEJACK_DIR/init.rb~.  The
+most notable thing to have ~init.rb~ is ~add_alias~.  An example:
+#+begin_src ruby
+  add_alias sc: :scaffold,
+            ls: :list,
+            i: :info
+#+end_src
+
+Note that ~add_alias~ is not the same as ~alias~.  ~alias~ is a built-in
+Ruby feature, whereas ~add_alias~ is ~steeplejack~-specific; using ~alias~
+will not make the alias available as a ~steeplejack~ subcommand.
+** License
+~steeplejack~ is published under the [[http://gnu.org/licenses/gpl-3.0.html][GPLv3]] (or any later version).
diff --git a/steeplejack b/steeplejack
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+#!/usr/bin/ruby
+
+%w[erb yaml readline fileutils]
+  .map &(method :require)
+
+STEEPLEJACK_DIR = File.expand_path(ENV["STEEPLEJACK_DIR"]&.chomp("/") || "~/.steeplejack")
+STEEPLEJACK_RC  = "#{STEEPLEJACK_DIR}/init.rb"
+
+def erb(from:, to:, params:, options:)
+  File.write to, ERB.new(File.read(from), trim_mode: options).result_with_hash(params)
+end
+
+def get_params(params)
+  Hash[params.zip params.map {|p| Readline.readline p+": "}]
+end
+
+$commands = {
+  scaffold: "Deploy a scaffold",
+  list: "List available scaffolds",
+  info: "Show info on scaffold",
+  help: "Show this help"
+}
+
+def add_alias(hash)
+  hash.each do |from, to|
+    Kernel.alias_method from, to
+    $commands[from] = "Alias for #{to}"
+  end
+end
+
+def scaffold(name, dest)
+  puts "### Deploying \"#{name}\" to \"#{dest}\" ###"
+  
+  orig = "#{STEEPLEJACK_DIR}/#{name}"
+  yaml = "#{orig}/_scaffold.yml"
+  recipe = YAML.load_file yaml
+  
+  files = Dir.chdir(orig) do
+    Dir["**/**.erb"].map {|s| s.chomp ".erb" }
+  end
+
+  # We want to check the files as soon as possible
+  files.each do |file|
+    raise "File exists: #{dest}/#{file}" if File.exist? "#{dest}/#{file}"
+  end
+
+  params = get_params (recipe["parameters"] || recipe["params"])
+  options = recipe["erb_options"]
+  
+  FileUtils.mkdir_p dest
+  
+  files.each do |file|
+    puts "Writing \"#{file}\""
+    erb from: "#{orig}/#{file}.erb", to: "#{dest}/#{file}",
+        params: params, options: options
+  end
+  
+  puts "\"#{name}\" deployed successfully"
+end
+
+def list
+  if File.exist? STEEPLEJACK_DIR
+    (Dir.children(STEEPLEJACK_DIR)
+       .filter &(File.method :directory?))
+      .map {|p| p.chomp("/").split("/")[-1] }
+      .each &(method :puts)
+  end
+end
+
+def info(name)
+  puts File.read "#{STEEPLEJACK_DIR}/#{name}/_scaffold.yml"
+end
+
+def help
+  puts "#{$0}: generic scaffolding"
+  puts "usage: #{$0} SUBCOMMAND ARGS"
+  puts
+  puts "Available subcommands:"
+  $commands.each {|n, d| puts "  #{n}: #{d || "Not documented"}" }
+end
+
+def main
+  load STEEPLEJACK_RC if File.exist? STEEPLEJACK_RC
+  sub = ARGV[0]
+  if ["--help", "-h", nil].include? sub
+    help
+  elsif $commands.keys.include? sub.to_sym
+    send sub, *ARGV[1..-1]
+  else
+    raise "No subcommand \"#{sub}\""
+  end
+end
+
+main if $0 == __FILE__