From 9c12102d0bb4ca5d1e002e6e6e09813ff9bf4412 Mon Sep 17 00:00:00 2001
From: Dev & Sec <devnsec@devnsec.com>
Date: Sun, 8 Nov 2015 10:26:15 +0000
Subject: [PATCH] use `command -v` instead of `type`, and add comments for the
 `su_sudo` function

---
 letsencrypt-auto | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/letsencrypt-auto b/letsencrypt-auto
index 8626ab329..ce58488c4 100755
--- a/letsencrypt-auto
+++ b/letsencrypt-auto
@@ -14,11 +14,24 @@ VENV_PATH=${VENV_PATH:-"$XDG_DATA_HOME/$VENV_NAME"}
 VENV_BIN=${VENV_PATH}/bin
 
 if test "`id -u`" -ne "0" ; then
-  if type sudo 1>/dev/null 2>&1; then
+  if command -v sudo 1>/dev/null 2>&1; then
     SUDO=sudo
   else
+    # `sudo` command does not exist, use `su` instead.
+    # Because the parameters in `su -c` has to be a string,
+    # we need properly escape it
     su_sudo() {
       args=""
+      # This `while` loop iterates over all parameters given to this function.
+      # For each parameter, all `'` will be replace by `'"'"'`, and the escaped string
+      # will be wrap in a pair of `'`, then append to `$args` string
+      # For example, `echo "It's only 1\$\!"` will be escaped to:
+      #   'echo' 'It'"'"'s only 1$!'
+      #     │       │└┼┘│
+      #     │       │ │ └── `'s only 1$!'` the literal string
+      #     │       │ └── `\"'\"` is a single quote (as a string)
+      #     │       └── `'It'`, to be concatenated with the strings followed it
+      #     └── `echo` wrapped in a pair of `'`, it's totally fine for the shell command itself
       while [ $# -ne 0 ]; do
         args="$args'$(printf "%s" "$1" | sed -e "s/'/'\"'\"'/g")' "
         shift