Don't load everything on dumb terminals

zshrc

@@ -1,5 +1,13 @@
 #!/bin/zsh
 
+# Prevent any of this initialization in non-interactive (or emacs)
+# shell commands. It slows them down.
+[[ $TERM == "dumb" ]] && return
+
+function command_exists {
+    command -v "$1" &> /dev/null
+}
+
 # Source Prezto.
 if [[ -s "${ZDOTDIR:-$HOME}/.zprezto/init.zsh" ]]; then
   source ~/.zsh/preztorc