cat(1)

cat.rb

#!ruby1.9
# -*- coding: us-ascii -*-
Encoding.default_external = "ASCII-8BIT"
require "optparse"

def squeeze_blank
  re = /\A\Z/
  lfd = 0
  ->(block) do
    block.replace(
      block.lines.map{|line|
        line.tap{
          if re === line
            lfd += 1
            line.clear if lfd > 1
          else
            lfd = 0
          end
        }} * "")
  end
end

def show_tabs
  re = /\t/
  f = "^I"
  ->(block){block.gsub!(re){f}}
end

def show_nonprinting
  re1 = /[\x00-\x08\x0b-\x1f\x7f]+/
  re2 = /[\x80-\x9f]+/
  re3 = /[\xa0-\xfe]+/
  re4 = /[\xff]+/
  ->(block) do
    block.gsub!(re1) do |m|
      "^" + m.bytes.map{|b| (b ^ 0x40).chr} * "^"
    end
    block.gsub!(re2) do |m|
      "M-^" + m.bytes.map{|b| (b - 0x40).chr} * "M-^"
    end
    block.gsub!(re3) do |m|
      "M-" + m.bytes.map{|b| (b ^ 0x80).chr} * "M-"
    end
    block.gsub!(re4) do |m|
      "M-^?" * m.size
    end
  end
end

def number
  re = /^/
  f = "%6d\t"
  n = 0
  ->(block){block.gsub!(re){f % (n += 1)}}
end

def number_nonblank
  re = /^(?!$)/
  f = "%6d\t"
  n = 0
  ->(block){block.gsub!(re){f % (n += 1)}}
end

def show_ends
  re = /$\n/
  f = "$\n"
  ->(block){block.gsub!(re){f}}
end

def adjust(filters)
  order = [:squeeze_blank, :show_tabs, :show_nonprinting, :number, :number_nonblank, :show_ends]
  filters.tap{|f|
    f.uniq!
    f.delete(:number) if f.include?(:number_nonblank)
  }.sort_by(&order.method(:index))
end

def parse_options(argv)
  op = OptionParser.new
  op.banner = <<BANNER
Usage: cat [OPTION]... [FILE]...
Concatenate FILE(s), or standard input, to standard output.

BANNER
  filters = []
  op.on("-A", "--show-all", "equivalent to -vET"){argv.unshift(*["-v", "-E", "-T"])}
  op.on("-b", "--number-nonblank", "number nonempty output lines"){filters << :number_nonblank}
  op.on("-e", "equivalent to -vE"){argv.unshift(*["-v", "-E"])}
  op.on("-E", "--show-ends", "display $ at end of each line"){filters << :show_ends}
  op.on("-n", "--number", "number all output lines"){filters << :number}
  op.on("-s", "--squeeze-blank", "suppress repeated empty output lines"){filters << :squeeze_blank}
  op.on("-t", "equivalent to -vT"){argv.unshift(*["-v", "-T"])}
  op.on("-T", "--show-tabs", "display TAB characters as ^I"){filters << :show_tabs}
  op.on("-u", "(ignored)"){}
  op.on("-v", "--show-nonprinting", "use ^ and M- notation, except for LFD and TAB"){filters << :show_nonprinting}
  op.parse!(argv)
  adjust(filters).map!(&method(:__send__))
end

filters = parse_options(ARGV)
while block = ARGF.read(1024)
  filters.each{|filter| filter[block]}
  print block
end