Split CSS files so that there are no more than a given number of selectors in one style sheet. This is a tool to cope with Internet Explorer's limitation of max. 4095 selectors per stylesheet.

css_splitter.rake

require 'rake'
require 'css_splitter'

desc 'split css files'
namespace :css do

  task :split do
    infile = ENV['infile'] || raise("missing infile")
    outdir = ENV['outdir'] || File.dirname(infile)
    max_selectors = ENV['max_selectors'] || 4095

    CssSplitter.split(infile, outdir, max_selectors)
  end

  task :count_selectors do
    css_file = ENV['css_file'] || raise("missing css file")

    CssSplitter.count_selectors(css_file)
  end

end

css_splitter.rb

module CssSplitter

  def self.split(infile, outdir = File.dirname(infile), max_selectors = 4095)

    raise "infile could not be found" unless File.exists? infile

    rules = IO.readlines(infile, "}")
    return if rules.first.nil?

    charset_statement, rules[0] = rules.first.partition(/^\@charset[^;]+;/)[1,2]
    return if rules.nil?

    # The infile remains the first file
    file_id = 1
    selectors_count = 0
    output = nil

    rules.each do |rule|
      rule_selectors_count = count_selectors_of_rule rule
      selectors_count += rule_selectors_count

      # Nothing happens until the selectors limit is reached for the first time
      if selectors_count > max_selectors
        # Close current file if there is already one
        output.close if output

        # Prepare next file
        file_id += 1
        filename = File.join(outdir, File.basename(infile, File.extname(infile)) + "_#{file_id.to_s}" + File.extname(infile))
        output = File.new(filename, "w")
        output.write charset_statement

        # Reset count with current rule count
        selectors_count = rule_selectors_count
      end

      output.write rule if output
    end
  end

  def self.count_selectors(css_file)
    raise "file could not be found" unless File.exists? css_file

    rules = IO.readlines(css_file, '}')
    return if rules.first.nil?

    charset_statement, rules[0] = rules.first.partition(/^\@charset[^;]+;/)[1,2]
    return if rules.first.nil?

    rules.inject(0) {|count, rule| count + count_selectors_of_rule(rule)}.tap do |result|
      puts File.basename(css_file) + " contains #{result} selectors."
    end
  end

  def self.count_selectors_of_rule(rule)
    rule.partition(/\{/).first.scan(/,/).count.to_i + 1
  end
  
end

This does appear to have a bug, in that it will split in the middle of a media query... Discovered this at the top of my second of split files...

@charset "UTF-8";

  /* line 8, ../scss/global/_mixins.scss */
  tr.hidden-lg {
    display: table-row !important;
  }

  /* line 9, ../scss/global/_mixins.scss */
  th.hidden-lg,
  td.hidden-lg {
    display: table-cell !important;
  }
}

Note the hanging bracket which is closing a media query which was opened in the first of the split css files.... Anyone able to factor this case into the snippet?

Hello.
I'm not familiar with ruby, but i tried to fix this tool to suit my needs:
IE have limits not only on selector count but also *.css file size, sometimes fat stylesheets files can throw errors in IE (something like: Out of memory at line XXX.) So we need to split first 4095 selectors in separate file too and include them instead of full css file.
for example:

<!-- ie 10 and above and all other browsers -->
<!--[if gt IE 9]><!-->
<link type="text/css" rel="stylesheet" media="all" href="css/screen.css" />
<!--<![endif]-->
<!-- only ie 9 and below -->
<!--[if lte IE 9]>
  <link type="text/css" rel="stylesheet" media="all" href="css/screen_1.css" />
  <link type="text/css" rel="stylesheet" media="all" href="css/screen_2.css" />
<![endif]-->

If you have same issues check my gist, it works perfect:
https://gist.github.com/todesstoss/1c3ac8310de7714a65e6

Thanks.

Hi,

Has anyone overcome the issue of media queries that t22james has ran into? This issue seems like a mayor bug and reason not to use this script to me, but since it's about 4 years old by now, maybe someone has already fixed it.

Thanks in advance

I'm having same media query split problem.as @t22james