Ruby version of rename function in linux for use with mac osx. Rename files ex. rename .txt .bak *.txt

rename.rb

#!/usr/bin/ruby
opts = []
args = []

ARGV.each do |a|
	if a =~ /^(-[a-zA-Z]+)/
		opts << a
	else
		args << a
	end
end

if args.empty? && opts.empty?
  puts "ex. rename .bak .txt *.bak"
  puts "or rename 'regex' *.mp3" 
  exit
end

arg_one = args[0]
arg_two = args[1]
files = nil

check_args = Proc.new {|opt|
  ex_opts = {:r => "downcase", :n => ""}
  if arg_one.nil? || arg_two.nil?
    if opt
      puts "option -#{opt} requires two arguments"
      puts "ex. rename -#{opt} #{ex_opts[opt.to_sym]} *"
    else
      puts "rename requires two arguments"
    end
    exit
  end
  files = opt == "-r" || opt.nil? ? args.drop(1) : args
  if files.size == 0 
    puts "no files matched: #{arg_two}"
    exit
  end
}

opts.each do |o|
  # TODO add option support
  # do something
  # puts o
  case o
       # option -r for ruby means do a ruby function to the file name
       # rename -r downcase *     
       when /-.*r.*/
          check_args.call(o)
          files.each do |f|
            begin
                was = f
                f = eval("f.dup.#{arg_one}")
                next if was == f 
                File.rename(was, f)
            rescue
              puts "option -r requires the second argument to be file names"
              puts "ex. rename -r upcase fIleThatItHoUgHtExIst.txt"
            end 
          end
          exit
       # option -n for numbers means add a number to file name
       # rename -n * 
       when /-.*n.*/
          check_args.call(o)
          n = 1
          files.each do |f|
            begin
              was = f 
              f = File.basename(f, File.extname(f)) + n.to_s + File.extname(f) 
              n += 1 
              next if was == f
              File.rename(was, f)
            rescue
              puts "option -n requires the 1st argument be file names"
              puts "ex. rename -n *.txt" 
            end
          end
          exit
        when /-.*h.*/
          puts "Usage: rename .bak .txt *.bak"           
          puts "or rename 'regex' *.mp3" 
          puts "or rename -r [ruby function] *.txt"
          puts "or rename -n *.txt"
          puts "or rename -h"  
          exit
       else  
       # default option ?
  end 
end
# change extensions?
if arg_one =~ /\.\w{1,4}$/            
  files = args.drop(2) # `ls *#{arg_three}`
  files.each do |f|
    f = f.strip
    f_name = File.basename(f, arg_one)
    if f_name
      File.rename(f, f_name + arg_two) # `mv #{i} #{f_name}#{arg_two}`
    end
  end  
# change filenames
else  
  check_args.call(nil)
  files.each do |f|
    f = f.strip
    f_name = File.basename(f)
    nf_name = f_name.gsub(Regexp.new(arg_one), '')
    if f_name
      File.rename(f_name, nf_name) # `mv #{f_name} #{nf_name}`
    end
  end
end

ruby_func.sh

rename(){
ruby ~/rename.rb $*
}