To set both titles from vim, use its termcap-title options to push the title to screen using the iconstring. When not running under screen, the right titlestring escapes will be inferred from terminfo.

set title
auto BufEnter * let &titlestring = s:MyTitle()

if &term =~ 'screen\(\.\(xterm\|rxvt\)\(-\(256\)\?color\)\?\)\?'
  " Set the screen title using the vim "iconstring"."
  set t_IS=^[k
  set t_IE=^[\
  set icon
  auto BufEnter * let &iconstring = &titlestring
  " Set the xterm title using the vim "titlestring"."
  set t_ts=^[]2;
  set t_fs=^G
endif

where the underlined characters are actual escapes input with ^V, not with literal carets.

As for generating a fancy title string like vim: there are some gotchas. The biggest is that vim does not preserve logical directory names, so getcwd() will resolve symlinks, leading to a different location string than generated by zsh’s %~. Rather than call pwd -L, we might as well unify the expansion syntax and call zsh. Of course, it’s nice to have a fallback, too:

" Perform zsh-like prompt expansion using the template {prompt}.  See
" "EXPANSION OF PROMPT SEQUENCES" in zshmisc(1).
function s:ZshPromptExpn(prompt)
  if &shell == "/bin/zsh"
    return system("print -Pn " . shellescape(a:prompt))
  else
    " Fallback to poor man's prompt expansion.
    " By no means equivalent to zsh.
    let idx = 0
    let result = ''
    let escapere = '%\([%)m]\|\(\(-\?[0-9]\+\)\?[~]\)\)'
    while idx < len(a:prompt)
      let nextesc = match(a:prompt, escapere, idx)
      if nextesc < 0
        let result .= a:prompt[idx :]
        break
      elseif idx < nextesc
        let result .= a:prompt[idx : (nextesc - 1)]
      endif

      let idx = matchend(a:prompt, escapere, nextesc)
      let esc = a:prompt[nextesc : (idx - 1)]
      if esc == '%m'
        let result .= substitute(hostname(), '^\([^.]*\).*', '\1', '')
      elseif esc =~ '%-\?[0-9]*[~]'
        let result .= fnamemodify(getcwd(), ':~')[:-2]
      elseif esc == '%%'
        let result .= '%'
      endif
    endwhile
    return result
endfunction

function s:MyTitle()
  return s:ZshPromptExpn("%m:%-3~ ") .
  \ v:progname . " " . fnamemodify(expand("%:f"), ":.")
endfunction

foo --bar

becomes “foo —bar”, which can look very similar to foo --bar if your contact is using a terminal that supports variable-width glyphs for exotic character points.

It’s a quick fix: stop double-hyphens being transformed to a long dash by right clicking the Adium input field, and unticking Substitutions > Smart Dashes from the menu.

Getting nice prompts is a common need and there is plenty of information out there on setting your PS1, but for various reasons I’ve had problems finding a ‘nice’ setup that’s just worked exactly the way I’ve wanted it to with titles. Here are the pertinent parts of my working configuration:

• I get the working directory and current command in the title
• I get the title in the screen windowlist if running in screen
• I get the same title in the WM_NAME of an rxvt or xterm, or the titlebar of an iTerm2, whether or not screen is involved

Here’s how I set my PS1 in .zshrc:

case "$TERM" in
  # [skipping some esoteric terminal emulators...]

  screen|screen.rxvt)
     # Set a coloured prompt
     PS1=$'%{\e[00;32m%}%*%{\e[00;34m%}%2~ %# %{\e[00m%}'
     ;;
  rxvt|rxvt-unicode|xterm|xterm-color)
     # Set the title, and a coloured prompt containing some useful info
     PS1=$'%{\e]0;%-3~\a\e\[00;32m%}%*%{\e[00;30m%}!%! %{\e[00;34m%}%2~ %# %{\e[0m%}'
     ;;
esac

I want an abbreviated form of the full command line so that it will fit in awesome's tasklist. I set the titles before a command is run in zsh's preexec hook. The screen window title and the xterm title are set with two different escapes.

function preexec() {
  local a=${${1## *}[(w)1]}  # get the command
  local b=${a##*\/}   # get the command basename
  a="${b}${1#$a}"     # add back the parameters
  a=${a//\%/\%\%}     # escape print specials
  a=$(print -Pn "$a" | tr -d "\t\n\v\f\r")  # remove fancy whitespace
  a=${(V)a//\%/\%\%}  # escape non-visibles and print specials

  case "$TERM" in
    screen|screen.*)
      # See screen(1) "TITLES (naming windows)".
      # "\ek" and "\e\" are the delimiters for screen(1) window titles
      print -Pn "\ek%-3~ $a\e\\" # set screen title.  Fix vim: ".
      print -Pn "\e]2;%-3~ $a\a" # set xterm title, via screen "Operating System Command"
      ;;
    rxvt|rxvt-unicode|xterm|xterm-color|xterm-256color)
      print -Pn "\e]2;%m:%-3~ $a\a"
      ;;
  esac
}

This requires the title to be reset for screen (since it’s not reset by PS1), using zsh’s precmd hook:

function precmd() {
  case "$TERM" in
    screen|screen.rxvt)
      print -Pn "\ek%-3~\e\\" # set screen title
      print -Pn "\e]2;%-3~\a" # must (re)set xterm title
      ;;
  esac
}

The beauty of this method (unlike methods that bind screen’s status line escapes to xterm Operating System Command escapes) is that no termcapinfo hacks in .screenrc are necessary.

Update: changed preexec to use zsh subscripting rather than splitting by IFS. Fixes duplication of 0-argument commands, e.g. “top top”.

The Option has a somewhat unorthodox binary format with non-power-of-2-width fixed point reals. To make generating the DHCP configuration statements easier, I developed a web-based RFC 3825 location configuration generation tool. It’s all client-side and even has a Google Maps preview of the location!

Copy the configuration to your local DHCP server, grab an appropriate geolocation library, and you’re ready to go! The tool generates a DHCP LCI Option for both dnsmasq and ISC’s dhcpd.

The lack of fixed point integers in Javascript made the implementation a little trickier than it would have been in, say, C.

Other lessons: Google Maps is not highly accurate.