Using ruby to write file from template

Question

I am making a few ruby scripts to write an nginx configuration file.

I have two files: one is a template with a few placeholders and the second stores a serialised hash with all information I need.

The information consists of a generic name of an application, an url, the number of ports to be used and the first port.

I'll make a short example to make it clear. This is my template:

Template file:

upstream thin {
    {upstream}
}
server {
    listen 80;
    server_name .{url};
    root /var/www/{name};
}

This is, more or less, how the information is stored in the second file with a ruby code:

Ruby script that saves the info:

apps = Hash.new { |h, k| h[k] = Hash.new }
apps["foo"] = {"url" => "foo.co.uk", "ports" => 3, "first" => 3000 }
apps["bar"] = {"url" => "bar.com", "ports" => 2, "first" => 3003 }

serialisedApps = Marshal.dump(apps)
File.open('/home/deploy/data/apps', 'w') {|f| f.write(serialisedApps) }

Now I can load this information like this:

apps = Marshal.load File.read('/home/deploy/data/apps')

And I can iterate through my hashes and print the ports for foo (3000, 3001 and 3002) and bar (3003 and 3004).

apps.each {|key, value|
  pn = value["ports"]
  fp = value["first"]

  pn.times do |i|
    currPort = fp + i
    puts "#{key} in port #{currPort}"
  end
}

Now, I need to get that template and replicate 2 files (for 'foo' and 'bar') like so:

upstream thin {
    server 127.0.0.1:3000;
    server 127.0.0.1:3001;
    server 127.0.0.1:3002;
}
server {
    listen 80;
    server_name .foo.co.uk;
    root /var/www/foo;
}

Now I just need to load the template, replace the placeholders and save it elsewhere. I managed to do that with a bash script, but I want to avoid it and use only ruby. Is there a simple way of doing that?

Thanks in advance!

Answer 1

Look into using using ERB. http://ruby-doc.org/stdlib-1.9.3/libdoc/erb/rdoc/ERB.html

It's built into Ruby's standard library, and does exactly what you want.