#!/bin/bash
free=$(free -mt | grep Total | awk '{print $4}')
if [ $free -lt 256 ]; then
date
echo Warning, free memory is ${free} mb only.
date
fi

[root@server ~]# sh /tools/mem.sh
Fri Dec 19 11:19:44 CET 2014
Warning, free memory is 245 mb only.
Fri Dec 19 11:19:45 CET 2014

sh /tools/mem.sh | mail -s "Server Low Memory" email@me.com

sh /tools/mem.sh 2>&1 > /dev/null | mail -s "Server Low Memory" email@me.com
sh /tools/mem.sh > /dev/null | mail -s "Server Low Memory" email@me.com

sh /tools/mem.sh >/dev/null 2>/tools/mem.txt ; if [ -s /tools/mem.txt ] ; then mail -s "Server Low Memory" < /tools/mem.txt email@me.com ; fi