Writing about my shell init display. Why?

What?

So, when my shell starts up, it loads a bunch of modules, draws some fun stuff, and shows an in-line image based on the OS (using iTerm2’s image display protocol).

How?

First part, the modules. When my shell starts, it loads up all the files in $HOME/.zsh/modules.d/. This is just a simple loop through the directory–a normal unix-y list of files with a number at the front to indicate load order (e.g. 00-loadme-first.zsh or 99-unimportant.zsh). It then iterates over their initialisation functions. This is done in two phases, since some of the modules create a global array or register helper functions that other modules may depend upon (notably the error handling putting info into the prompt line).

# Load modules from the dynamic module directory.
if [[ -d "$MODDIR" ]]; then
  for mod in ${MODDIR}/*.zsh; do
    source $mod
  done
fi

...

print -P "${CL_NORM_ON}Initializing modules...${CL_NORM_OFF}"
for mod_name mod_init in ${_aimee_zsh_modules}; do
  print "    $mod_name"
  eval $mod_init
done
print

These modules are created using my own module format/convention. They call a function module_add with a title and reference to an init function. For example, the module 80-iterm.zsh calls module_add "iTerm2" _aimee_iterm_init. Note that not all modules use this, notably the text image itself, which runs immediately upon load (so the print during initalisation is put inline along the image).

The text image (in 00-banner.zsh link) is drawn using a combination of zsh colour codes and terminal escape sequences to move the cursor around. The cursor is moved back up to the top-left of where this sequence started (just below the ruler). This is so that the subsequently loaded modules will announce themselves along side the image.

IFS="" read -r -d '' TEXT << '__EOF'
%F{magenta}0---------1---------2---------3---------4---------5---------6---------7--------7%f
%F{magenta}01234567890123456789012345678901234567890123456789012345678901234567890123456789%f

DRAWINGS GO HERE

%f%b
\033[16A
__EOF
print -P "${TEXT}"

The actual image portion (in 98-term-ident.zsh link) is done using iTerm2’s image support. The script tries to be smart and show the stylised ascii OS name along side a blank space when running within a terminal that does not support real images (e.g. Terminal.app or tmux). This is the essential bit of code, where the text is written, the curosr is moved back up to the top, and then either the PNG or a few blank lines are rendered.

case "${SYSNAME}" in
  Darwin)
    # src file: "distro-darwin.png"
    IMGDATA="BASE64-ENCODED-PNG-FILE-GOES-HERE"
    IFS="" read -r -d '' TEXT << '__EOF'
             ____                      _
            / __ \____ _______      __(_)___
           / / / / __ `/ ___/ | /| / / / __ \
          / /_/ / /_/ / /   | |/ |/ / / / / /
         /_____/\__,_/_/    |__/|__/_/_/ /_/
\033[7A
__EOF
  ;;

  ...
esac

if [[ -n "${IMGDATA}" ]]; then
  echo
  echo "${TEXT}"
  if [[ "${LC_TERMINAL:-}" == "iTerm2" && -z $(__iterm2_is_tmux) ]]; then
    __iterm2_print_image "" 1 "${IMGDATA}" 0 "" "5" "1" ""
  else
    echo; echo; echo; echo; echo
  fi
  echo
fi

Show me!

What’s the result of all this? Here is what launching a new shell instance looks like on two different systems: my macOS laptop, and, a Linode I have configured a Tailscale exit node.