Interpret bin/oct/dec/hex number(s) in specified character encoding and try to convert to UTF-8, then display the result if possible.

chars.rb

#!/usr/bin/env ruby

# -----------------------------------------------------------------------------
# chars: interpret bin/oct/dec/hex number(s) in specified character encoding
#        and try to convert to UTF-8, then display the result if possible.
# (C) 2021 J. R. Schmid <jrs@weitnahbei.de>
# May be shared and used according to CC BY-SA 4.0
# (https://creativecommons.org/licenses/by-sa/4.0/)
# -----------------------------------------------------------------------------

require 'slop'         # gem install slop
require 'colorize'     # gem install colorize
require 'unicode/name' # gem install unicode-name

def print_usage
  warn "Usage: #{File.basename(__FILE__)} [options] <arg1> <arg2> <...>"
  warn ""
  warn "  options (unless -f is specified, numbers are expected as arguments):"
  warn ""
  warn "  -l|--list-encodings: do nothing except list all known encodings"
  warn "  -e|--encoding <comma separated list | all> (default: utf-8)"
  warn "  -b|--base <bin|oct|dec|hex> (default: numbers are interpreted as hexadecimals)"
  warn "  -n|--with-names: also show each codepoint's UTF-8 name if possible"
  warn "  -f|--forward: expect strings of characters as input instead of numbers; implies -n"
  warn ""
  exit
end

begin
  @opts = Slop.parse do |o|
    o.string '-e', '--encoding',      ''
    o.string '-b', '--base',          ''
    o.bool   '-l', '--list-encodings',''
    o.bool   '-n', '--with-names',    ''
    o.bool   '-f', '--forward',       ''
  end
rescue Slop::UnknownOption, Slop::MissingArgument, Slop::MissingRequiredOption
  print_usage
end

@opts[:encoding] ||= 'UTF-8'
@opts[:base] ||= 'hex'

@known_encodings = Encoding.list.map{|e| [e.to_s.downcase, e.to_s]}.to_h.sort.to_h
@encodings = []
if @opts[:list_encodings]
  @known_encodings.each{|k,v| puts k}
  exit
else
  print_usage unless @opts.arguments.any?
  @opts[:encoding].split(',').each do |encoding|
    (@encodings = @known_encodings.values; break) if encoding == 'all'
    @encodings << @known_encodings[encoding.downcase]
  end
end

def basex2dec(n)
  base = case @opts[:base].to_sym
    when :bin then 2
    when :oct then 8
    when :dec then return n.to_i
    when :hex then 16
    else print_usage
  end
  n.to_s.to_i(base)
end

def encode(i, encoding)
  i.chr(encoding)
end

def show_names(chars, indent: '')
  chars.each do |char|
    char = char.encode(Encoding::UTF_8)
    puts "#{indent}#{char.blue}:\t#{Unicode::Name.of(char)}"
  end
end

def nums_to_chars(encoding)
  chars = []
  begin
    @opts.arguments.each{|n| chars << encode(basex2dec(n.downcase.gsub(/([\da-f]+)/, '\1')), encoding)}
    print "#{encoding} codepoints as hexadecimals: "; pp chars
    puts "As displayed by terminal in #{encoding}: \"#{chars.join.blue}\""
    puts "As displayed by terminal after conversion from #{encoding} to UTF-8: \"#{chars.join.encode(Encoding::UTF_8).light_blue}\""
    show_names(chars, indent: "\t") if @opts[:with_names]
  rescue RangeError => e
    warn "(#{e.message})"
  rescue Encoding::UndefinedConversionError,
         Encoding::UndefinedConversionError,
         Encoding::CompatibilityError,
         Encoding::ConverterNotFoundError => e
    warn "(converting from #{encoding} to UTF-8 not possible: #{e.message.yellow})"
  end
  puts
end

@encodings.each do |encoding|
  if @opts[:forward]
    show_names @opts.arguments.join(' ').chars
  else
    nums_to_chars(encoding)
  end
end