Display separator when purpose is defined

Install/Templates/home/config/fish/functions/fish_prompt.fish

@@ -31,6 +31,11 @@ function fish_prompt --description 'Write out the prompt'
     end
 
     # Purpose
+    set -q FISH_SHELL_PURPOSE
+    if test $status -eq 0
+        set_color normal
+        echo -n '['
+    end
     set_color blue
     echo -n $FISH_SHELL_PURPOSE
     set_color normal