if

• if开头,fi结尾
• 单分支if语句

if [ 判断 ];then
    program
fi

if [ 判断 ]
    then
        program
fi

统计根分区使用率写提醒脚本

#!/bin/bash
rate=$(df -h | grep "/dev/vda1" | awk 'print $5' | cut -d "%" -f 1)

if [ $rate -lt 80]
    then 
        echo "/dev/vda1 is lower than 80%"
fi

---

#!/bin/bash
rate=$(df -h | grep /dev/vda1 | awk '{print $5}' | awk 'BEGIN{FS="%"}{print $1}')
if [ $rate -lt 80 ];then
    echo "/dev/vda1 's capacity lower than 80"
fi

注意:

1. 用awk也行

   rate=$(df -h | grep /dev/vda1 | awk '{print $5}' | awk 'BEGIN{FS="%"}{print $1}')

2. 比较中,$rate前面加\$引用变量

• 多分支

  if [ 判断 ]
      then 
          program
      else 
          program
  fi

  打包备份/etc目录:

  #!/bin/bash
  date=$(date +%y%m%d)
  size=$(du -sh /etc)
  if [ -d /tmp/dbback ]
      then
          echo "Date is:$date">/tmp/dbback/db.txt
          cd /tmp/dbback
          tar -zcf etc_$date.tar.gz /etc db.txt &> /dev/null
          rm -rf /tmp/dbback/db.txt
      else 
          mkdir /tmp/dbback
          echo "Date is:$date" > /tmp/dbback/db.txt
          cd /tmp/dbback
          tar -zcf etc_$date.tar.gz /etc db.txt &> /dev/null
          rm -rf /tmp/dbback/db.txt
  fi

  解释:

1. 判断是否存在/tmp/dbback这个目录
2. 有就备份,没有就创建
3. 进入这个目录作为相对路径
4. 打包后 删除原来的文件
   一个

• yum -y install nmap安装远程扫描命令
• yum -y install httpd安装apache
• nmap -sT ip地址 看80端口开了没
  nmap -sT ip | grep 'http$' | awk '{print $2}',截取端口状态
  写一个脚本

  #!/bin/bash
  port=$(nmap -sT ip | grep 'http$' | awk '{print $2}')
  if [ "$port" == "open" ];then
      echo "$(date) httpd is open!" >> /tmp/autostart.acc.log
      else 
          #没有启动则重启
          /etc/rc.d/init.d/httpd start &> /dev/null
          echo "$(date) restart httpd ">> /tmp/autostart.err.log
  fi

  if elseif else

  if [ 判断 ];then
      program
  elif 
      then
          program
  else 
      program
  fi

---

if [ 判断 ]
    then
        program
elif
    then 
        program
else 
    program
fi

判断文件类型脚本

#!/bin/bash
read -p "Please input a filename:" file

if [ -z "$file" ] 
    then 
        echo "Error,please input a filename"
        exit 1
elif [ ! -e "$file" ] 
    then 
        echo "Your input is not a file"
        exit 2
elif [ -f "$file" ] 
    then 
        echo "$file is a regular file"
elif [ -d "$file" ]
    then 
        echo "$file is a directory"
else 
    echo "$file is an other file"
fi  

case 语句

1. 和if一样,结束语都要导致
2. program语句要以;;结尾

   case $val in
       1)
           echo "1";;
       2)
           echo "2";;
       3) 
           echo "3";;
       4)
           echo "other";;
   esac

   例如:

   #!/bin/bash
   read -t 30 -p "Please input you choose" choose
   case $choose in
       1)
           echo "1";;
       2) 
           echo "2";;
       3)
           echo "3";;
       *)
           echo "other";;
   esac

for

1. 在文件中操作

   for 变量 in value1 v2 v3...
       do
           program
       done
       

---

#!/bin/bash
for i in 1 2 3 4 5
    do 
        echo $i
    done 

• 例:统计当前文件夹下.sh文件数量

  #!/bin/bash
  cd /tmp/sh/
  cnt=0
  for i in $(ls *.sh)
      do 
          cnt=$(( $cnt + 1 )) 
          echo "$i"
      done
  echo "文件数量=$cnt"

2. c语法,在(( ))数值运算符内

   for ((i=1; i<=100; i++))
       do
           program
       done 

   例:

   #!/bin/bash
   cnt=0
   for ((i=1; i<=100; i++))
       do
           cnt=$(( $cnt + $i )) 
       done
   echo $cnt

while / until

1. #!/bin/bash
   i=100
   while [ $i -ge 10 ]
       do
           echo "$i"
           i=$(( $i - 1 ))
       done

2. until:直到 条件成立 就 终止

   #!/bin/bash
   sum=0; i=1
   until [ $i -gt 100 ]
       do
           $sum=$(( $sum + $i ))
           $i=$(($i+1))
       done
   echo $sum