Quick script to select subset of password list

pwd.rb

#!/usr/bin/ruby
# ruby this.rb <wordlist> <command> <param> [cmd]
# Ex. C:\Users\Brad Krane\Documents\src\pwd>ruby pwd.rb 10-million-password-list-top-1000000.txt letters 5 "echo Weak PWD"       
#Weak password
#Weak qwerty
#Weak dragon
#Weak baseball
#Weak football
throw ArgumentError.new "Invalid aruments: #{ARGV}\nruby this.rb <wordlist> <command> <param> [cmd]" if ARGV.length > 4 || ARGV.length < 3

FILE=ARGV.shift
CMD=ARGV.shift.downcase
PARAM=ARGV.shift.to_i
SHCMD=ARGV.shift

pwds = File.readlines(FILE,chomp:true)

selected = case CMD
when 'random'
  pwds.shuffle[0..PARAM-1]
when 'length'
  pwds.select { |pwd| pwd.length == PARAM }
when 'first'
  pwds[0..PARAM-1]
when 'last'
  pwds[-PARAM..-1]
when 'letters'
  pwds.select { |pwd|
   begin
    pwd.gsub(/[a-z]/i,'') == ''
   rescue => e
    false
   end
  }[0..PARAM-1]
when 'numbers'
  pwds.select { |pwd|
   begin
    pwd.gsub(/[0-9]/i,'') == ''
   rescue => e
    false
   end
  }[0..PARAM-1]
when 'lessthan'
  pwds.select { |pwd| pwd.length < PARAM }
when 'greaterthan'
  pwds.select { |pwd| pwd.length > PARAM }
else
 throw ArgumentError.new "Unknown command: #{CMD}"
end

if SHCMD == nil
  selected.each { |pwd| print "#{pwd}\n" }
else
  selected.each { |pwd| system "#{SHCMD.sub('PWD', pwd)}\n" }
end