Convert history files from bash to zsh and vice versa

bash2zsh_hist.rb

#!/usr/bin/ruby
# Convert history files from bash to zsh and vice versa.
# Usage:
# cat ~/.bash_history | ruby bash2zsh_hist.rb > ~/.zsh_history
# cat ~/.zsh_history | ruby bash2zsh_hist.rb -r > ~/.bash_history

require 'set'

class Integer
	# https://github.com/zsh-users/zsh/blob/dd13048b3b8cf710f44424ce9fedc2b56c31fde3/Src/utils.c#L4082-L4189
	@@typtab = [0, 0x83, 0xa2,].to_set.merge(0x84..0x9c).merge(0x9d..0xa1)

	# https://github.com/zsh-users/zsh/blob/dd13048b3b8cf710f44424ce9fedc2b56c31fde3/Src/ztype.h#L60
	def imeta?
		@@typtab === self
	end
end

class String
	META = 0x83

	# https://github.com/zsh-users/zsh/blob/dd13048b3b8cf710f44424ce9fedc2b56c31fde3/Src/utils.c#L4755-L4840
	def metafy
		result = ''
		each_byte do |c|
			if c.imeta?
				result << META.chr << (c ^ 32).chr
			else
				result << c.chr
			end
		end
		result.force_encoding(encoding)
	end

	# https://github.com/zsh-users/zsh/blob/dd13048b3b8cf710f44424ce9fedc2b56c31fde3/Src/utils.c#L4865-L4888
	def unmetafy
		result = ''
		meta = false
		each_byte do |c|
			if meta
				result << (c ^ 32).chr
				meta = false
			elsif c == META
				meta = true
			else
				result << c.chr
			end
		end
		result.force_encoding(encoding)
	end

	def bash_timestamp?
		start_with? '#' and length == 11 and self =~ /^#\d{10}$/
	end

	attr_reader :zsh_ts, :zsh_cmd
	def zsh_timestamp?
		return @have_zsh_ts if defined? @ts
		@have_zsh_ts = start_with?(': ') && self =~ /^: (\d{10}):\d+;(.+)$/
		@zsh_ts, @zsh_cmd = $1, $2 if @have_zsh_ts
		@have_zsh_ts
	rescue ArgumentError
		warn "\nSkipping line #$. because of #$!\n#{inspect}"
	end
end

class History
	def self.bash2zsh
		hist_entry = ''
		timestamp = false
		while gets
			line = $_.chop
			if line.bash_timestamp?
				timestamp = true
				puts hist_entry + "\n" unless hist_entry.empty?
				hist_entry = ": %s:0;" % line[1..-1]
				lines = 0
			elsif timestamp
				hist_entry << "\\\n" unless lines == 0
				hist_entry << line.metafy
				hist_entry << ' ' if line.end_with? "\\"
				lines += 1
			end
		end
		puts hist_entry + "\n" if timestamp and not hist_entry.empty?
	end

	def self.zsh2bash
		hist_entry = ''
		while gets
			line = $_.chop.unmetafy
			if hist_entry.empty? and line.zsh_timestamp?
				ts, cmd = line.zsh_ts, line.zsh_cmd
				if cmd.end_with? "\\"
					cmd.slice!(-1)
					cmd.slice!(-1) if cmd.end_with? "\\ "
					hist_entry = "#%s\n%s\n" % [ts, cmd]
				else
					cmd.slice!(-1) if cmd.end_with? "\\ "
					puts "#%s\n%s" % [ts, cmd]
				end
			elsif not hist_entry.empty?
				if line.end_with? "\\"
					line.slice!(-1)
					line.slice!(-1) if line.end_with? "\\ "
					hist_entry << line << "\n"
				else
					line.slice!(-1) if line.end_with? "\\ "
					puts hist_entry + line + "\n"
					hist_entry = ''
				end
			end
		end
	end
end

reverse = ARGV.shift if ARGV[0] == '-r' || ARGV[0] == '--reverse'

reverse ? History.zsh2bash : History.bash2zsh