linux运行java项目时，指定当前空闲内存的80%运行项目，shell脚本获取当前80%空闲内存值的方法

MEMORY=`free | sed -n '2p' | awk '{print $4}'`

USE_MEMORY_RATE=0.8

## 判断USE_MEMORY_RATE 值是否在0~1之间
PRODUCT=`bc << EOF
scale = 0
a1 = $USE_MEMORY_RATE
b1 = 10
a1 * b1
EOF`
index=`expr index "${PRODUCT}" .`
if [[ $index -ne 0  ]];then
  PRODUCT=${PRODUCT:0:${index}-1}
fi

if [[ $PRODUCT -ge 10 ]];then
  echo "USE_MEMORY_RATE should be  greater than 0 and lower than 1,you set is ${USE_MEMORY_RATE}"
  exit
fi

if [[ $PRODUCT -le 0 ]];then
  echo "USE_MEMORY_RATE should be  greater than 0 and lower than 1,you set is ${USE_MEMORY_RATE}"
  exit
fi


# 算出80%内存的值，并进行取整。因为-Xmx 后不能跟小数
USE=`bc << EOF 
scale = 0
a1 = $MEMORY / 1024
b1 = $USE_MEMORY_RATE
a1 * b1 
EOF`
INDEX=`expr index "${USE}" .`
USE_MEMORY=${USE:0:${INDEX}-1}

echo "engine use memory  $USE_MEMORY M"