Lua script to restore ZSH history file from backups (useful for completion)

restore-zsh-history.lua

#!/usr/bin/env lua

-- Posted this online because of http://news.ycombinator.com/item?id=3535349

ordered = {}
index = {}
need_continuation = false
first_continued_line = 0

function add_or_replace(line)

  -- ZSH uses special markers when appending to the command history file which
  -- enables it to share the command history between concurrent ZSH sessions.
  -- When joining several history files however the markers should be removed:
  if line:find '^:%s%d+:%d;%s?.+' then
    -- Convert e.g. ": 1257020658:0;ls" to "ls".
    line = line:match '^:%s%d+:%d;%s?(.+)'
  end

  -- Add the line to the ordered list of commands.
  table.insert(ordered, line)

  -- Detect the range of multi-line commands.
  local backcont = need_continuation -- previous line indicated continuation.
  local forwcond = line:find '\\$' -- current line indicates continuation.
  need_continuation = forwcond
  local first_line = #ordered
  local last_line = first_line
  local index_key = line:gsub('^%s*(.-)%s*$', '%1')
  if forwcond and not backcont then
    -- First line of multi-line command.
    first_continued_line = first_line
    -- Don't add this line to the index.
    index_key = nil
  elseif backcont and not forwcond then
    -- Last line of multi-line command.
    first_line = first_continued_line
    -- Create index key from concatenated lines.
    index_key = {}
    for i = first_line, last_line do
      table.insert(index_key, ordered[i])
    end
    index_key = table.concat(index_key, '\n')
  elseif backcont or forwcond then
    -- Don't add this line to the index.
    index_key = nil
  end
  if index_key then
    if index[index_key] then
      -- Hide previous occurrence of command.
      local r = index[index_key]
      for i = r[1], r[2] do ordered[i] = '' end
    end
    index[index_key] = {first_line, last_line}
  end
end

-- Collect the command history of the last year or so from my backups:
pipe = io.popen("ssh my-backup-server 'cat $HOME/Backups/Laptop/*/home/peter/.z_history'", 'r')
for line in pipe:lines() do add_or_replace(line) end
pipe:close()

-- Now merge it with the command history on my laptop:
file = io.open('/home/peter/.z_history', 'r')
for line in file:lines() do add_or_replace(line) end
file:close()

-- Print the results.
for i = 1, #ordered do
  local line = ordered[i]
  if line ~= '' then
    io.write(line, '\n')
  end
end