class Linguist::Shebang

def self.call(blob, candidates)

If the candidate list is empty, any language is a valid candidate.
blob's shebang is valid. Returns an empty list if there is no shebang.
Returns an array of languages from the candidate list for which the

Shebang.call(FileBlob.new("path/to/file"))

Examples

candidates - A list of candidate languages.
blob - An object that quacks like a blob.

Public: Use shebang to detect language of the blob. 
def self.call(blob, candidates)
  return [] if blob.symlink?
  languages = Language.find_by_interpreter interpreter(blob.data)
  candidates.any? ? candidates & languages : languages
end

def self.interpreter(data)

Returns a String or nil

Public: Get the interpreter from the shebang 
def self.interpreter(data)
  # First line must start with #!
  return unless data.start_with?("#!")
  shebang = data[0, data.index($/) || data.length]
  s = StringScanner.new(shebang)
  # There was nothing after the #!
  return unless path = s.scan(/^#!\s*\S+/)
  # Keep going
  script = path.split('/').last
  # if /usr/bin/env type shebang then walk the string
  if script == 'env'
    s.scan(/\s+/)
    while s.scan(/((-[i0uCSv]*|--\S+)\s+)+/) || # skip over optional arguments e.g. -vS
          s.scan(/(\S+=\S+\s+)+/) # skip over variable arguments e.g. foo=bar
      # do nothing
    end
    script = s.scan(/\S+/)
  end
  # Interpreter was /usr/bin/env with no arguments
  return unless script
  # "python2.6" -> "python2"
  script.sub!(/(\.\d+)$/, '')
  # #! perl -> perl
  script.sub!(/^#!\s*/, '')
  # Check for multiline shebang hacks that call `exec`
  if script == 'sh' &&
    data.lines.first(5).any? { |l| l.match(/exec (\w+)[\s"']+\$0[\s"']+\$@/) }
    script = $1
  end
  # osascript can be called with an optional `-l <language>` argument, which may not be a language with an interpreter.
  # In this case, return and rely on the subsequent strategies to determine the language.
  if script == 'osascript'
    return if s.scan_until(/\-l\s?/)
  end
  File.basename(script)
end