Print segments of files at the same location.

slice

#!/usr/bin/env ruby
begin
require 'optparse'

offset=0
length=-1
lineno=nil
quiet=false

OptionParser.new do |opts|
  opts.banner = %{
Usage: #{$0} [options] FILES...

  Print segments of files at the same location. Use the -c option to integrate
  with cmp.

      echo abc > a
      echo aBc > b
      cmp a b | slice -c
      0 bc
      0 Bc

Options:
}.lstrip

  opts.on("-c", "--cmp-ouput", "show slice as per cmp output") do
    line = $stdin.gets
    case line
    when /^(\S+) (\S+) differ: char (\d+), line (\d+)/
      ARGV << $1 << $2
      offset = $3.to_i - 1
    when ""
      raise "no differences to show"
    else
      raise "input does not match expected cmp output -- -c cannot be used:\n#{line.inspect}"
    end
  end

  opts.on("-d", "debug mode") do
    $DEBUG = true
  end

  opts.on("-l", "--length LENGTH", Integer, "bytes to show (default reads to EOL)") do |value|
    length = value.to_i
  end

  opts.on("-L", "--line LINENO", Integer, "offset to line (override -o)") do |value|
    lineno = value.to_i
  end

  opts.on("-o", "--offset OFFSET", Integer, "bytes to offset (default #{offset}, cumulative)") do |value|
    offset += value.to_i
  end

  opts.on("-q", "--quiet", "do not print line/pos, usually MUCH quicker") do
    quiet = true
  end

  opts.on("-h", "--help", "print this help") do
    puts opts
    puts
    exit
  end
end.parse!

ARGV.each do |file|
  File.open(file == '-' ? 0 : file) do |io|
    line_number = 0

    if lineno
      lineno.times { io.readline }
      line_number = lineno
    elsif offset > 0
      if quiet
        io.pos = offset
      else
        chunk_size = 1024
        (offset / chunk_size).times { line_number += io.read(chunk_size).count("\n") }
        line_number += io.read(offset % chunk_size).to_s.count("\n")
      end
    end

    pos = io.pos
    content = length < 0 ? io.readline.chomp("\n") : io.read(length)

    if quiet
      puts content
    else
      puts "%d@%d %s" % [line_number, pos, content]
    end
  end
end

rescue Interrupt
  exit 130
rescue Errno::EPIPE 
  exit 0
rescue
  raise if $DEBUG
  $stderr.puts $!.message
  exit 1
end