themes: square: add short commit sha1 to prompt

TODO: this solution is ugly. Find a better way.

Signed-off-by: Michael Turquette <mturquette@deferred.io>

themes/square/square.theme.bash

@@ -1,7 +1,24 @@
 #!/usr/bin/env bash
 
+function git_short_sha() {
+  SHA=$(git rev-parse --short HEAD 2> /dev/null) && echo "$SHA"
+}
+
 prompt() {
-  PS1="${green}\w${reset_color} $(__git_ps1 [${red}%s${reset_color}])$ "
+  local sha="${yellow}$(git_short_sha)${reset_color}"
+  local branch="$(__git_ps1 ${red}%s${reset_color})"
+  # failed attempt to merge the two above
+  #local branch="$(__git_ps1 ${red}%s${reset_color} ${sha})"
+
+  # the original
+  #PS1="${green}\w${reset_color} $(__git_ps1 [${red}%s${reset_color}])$ "
+
+  # with persistent brackets
+  #PS1="${green}\w${reset_color} [${branch} ${sha}]$ "
+  # without any brackets
+  PS1="${green}\w${reset_color} ${branch} ${sha}$ "
+  # failed attempt at conditional brackets
+  #PS1="${green}\w${reset_color} ${branch}$ "
 }
 
 PROMPT_COMMAND=prompt