require 'haml'  # version 4.0.7

template = <<EOF
- if true
  %h1 {{SECTION_NO_1}}

- if false
  %h1 {{SECTION_NO_2}}

- if true
  %h1 {{SECTION_NO_3}}
EOF

engine = Haml::Engine.new(template)
puts engine.render

# output
# <h1>{{SECTION_NO_1}}</h1>
# <h1>{{SECTION_NO_3}}</h1>