perl_requirement: add

Library/Homebrew/requirements.rb

@@ -6,6 +6,7 @@ require "requirements/minimum_macos_requirement"
 require "requirements/maximum_macos_requirement"
 require "requirements/mpi_requirement"
 require "requirements/osxfuse_requirement"
+require "requirements/perl_requirement"
 require "requirements/python_requirement"
 require "requirements/java_requirement"
 require "requirements/ruby_requirement"

Library/Homebrew/requirements/perl_requirement.rb

+class PerlRequirement < Requirement
+  fatal true
+  default_formula "perl"
+
+  def initialize(tags)
+    @version = tags.shift if /^\d+\.\d+$/ === tags.first
+    raise "PerlRequirement requires a version!" unless @version
+    super
+  end
+
+  satisfy(:build_env => false) do
+    which_all("perl").detect do |perl|
+      perl_version = Utils.popen_read(perl, "--version")[/\(v(\d+\.\d+)(?:\.\d+)?\)/, 1]
+      next unless perl_version
+      Version.new(perl_version.to_s) >= Version.new(@version)
+    end
+  end
+
+  def message
+    s = "Perl #{@version} is required to install this formula."
+    s += super
+    s
+  end
+
+  def inspect
+    "#<#{self.class.name}: #{name.inspect} #{tags.inspect} version=#{@version.inspect}>"
+  end
+end