if语句实例

if 单分支
#!/bin/bash
RATE=`df -hT | grep "/boot" | awk '{print $6}' | cut -d "%" -f1 `
if [ $RATE -gt 80 ]
then
echo "Warning,DISK is full!"
fi

#!/bin/bash
#
DIR=/data/cache
DAY=`date +%Y%m%d%H`
NUM=`ls $DIR | wc -l`
DIRNAME=`ls $DIR | grep leveldb`
if [ $NUM -gt 3 ]
then
rm -rf $DIR/$DIRNAME
echo "-------$DAY--($DIR)-------" >> /tmp/img_cache.log
echo "$DIRNAME Deleted successful" >> /tmp/img_cache.log
fi

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if 双分支
#!/bin/bash
service httpdstatus &> /dev/null
if [ $? -eq 0 ]
then
echo “httpdservice is running."
else
/etc/init.d/httpd restart
fi

#!/bin/bash
ping -c 3 -i 0.2 -W 3 $1 &> /dev/null
if [ $? = "0" ]
then
echo "Host $1 is up !"
else
echo "Host $1 is down !!"
fi

#!/bin/bash
update=`uptime |awk -F " |," '{print $(NF-2)}'`
if [[ $update > 3 ]];then
echo "cpu超负荷!"
else
echo "cpu正常!"
fi

NR - Number of Record - 当前处理的行是第几行（因为awk是流处理工具，一行一行处理的，所以NR在不停的自增1)
FNR - File Number of Record - 当前处理的行是当前处理文件的第几行
NF - Number of Fileds - 当前行有多少列数据（这个在每行都会根据设定的分割符重新计算，默认分割符是任意连续的多个空白符）

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if 多分支
#!/bin/bash
read -p "Please enter your code: " NUMBER
if [ $NUMBER -lt 100 ] && [ $NUMBER -ge 90 ]
then
echo "Great"
elif [ $NUMBER -lt 90 ] && [ $NUMBER -ge 80 ]
then
echo "Nice"
elif [ $NUMBER -lt 80 ] && [ $NUMBER -ge 70 ]
then
echo "Good"
elif [ $NUMBER -lt 70 ] && [ $NUMBER -ge 60 ]
then
echo "Lucky"
else
echo "Bad"
fi
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