improved install script

install

@@ -1,9 +1,21 @@
 #! /usr/bin/env sh
 
-cp git-backup /usr/local/bin
-cp git-backup.conf /etc
-sed -i '/git-backup/c\' /etc/crontab
-echo "00 2    * * *   root    git-backup > /dev/null" >> /etc/crontab
-service cron reload
+dir="$(dirname $(readlink -f "${0}"))"
+
+cp "${dir}/git-backup" /usr/local/bin &&
+
+if [ ! -x /etc/cron.d/git-backup ]
+then
+  if [ ! -x /etc/git-backup.conf ]
+  then
+    cp "${dir}/git-backup.conf" /etc/git-backup.conf
+  fi &&
+
+  if [ ! -x /etc/cron.d/git-backup ]
+  then
+    echo "00 2    * * *   root    git-backup > /dev/null" > /etc/cron.d/git-backup
+  fi &&
+  service cron reload
+fi &&
 
 git-backup --init