메모리 사용율 script

#!/bin/bash
s_time=$(date +%Y-%m-%d' '%H:%M;%S)

while true; do
    #memory usage
    TOTAL=`free | awk '/^Mem:/ { print("%s\n", $2); }'`
    USED=`free | awk '/^Mem:/ { print("%s\n", $3); }'`
    FREE=`free | awk '/^Mem:/ { print("%s\n", $4); }'`
    BUFFERS=`free | awk '/^Mem:/ { print("%s\n", $6); }'`
    CACHED=`free | awk '/^Mem:/ { print("%s\n", $7); }'`
    #cat /proc/meminfo | egrep 'Mem Total|Mem Free |Buffers|Cached' | grep -v 'SwapCached' | awk '{print $2}' > $TMP_DIR/memory.$$
    usage=$(expr $FREE + $BUFFERS + $CACHED)
    used=`expr $TOTAL - $FREE - $BUFFERS - $CACHED`
    #mem_usage=`echo "$used / $TOTAL * 100" | bc -l`
    #mem_usage=$(echo "scale=2; $used/%TOTAL*100" | bc -l)
    let "mem_usage=$used*100/$TOTAL"
    if ["$mem_usage" -ge 90]; then
        Process=`/bin/ps -eo pmem,pcpu,rss,vsize,args | /bin/sort -k 1 -k | /usr/bin/head -n 20`
        echo -e "$(hostname) as on $s_time\n $Process\n" | mail -s "Alert:Almost out of memory space $mem_usage%" test@dvframes.com
    fi
    #Wait before checking again.
    sleep 300
done

linux, centos, 리눅스, 메모리, 사용율, 스크립트, 쉘, shell