shell 第五章 shell的执行流控制

一.for语句

作用：为循环执行动作
for语句结构：

for            定义变量
do            使用变量,执行动作
done         结束标志

1.for语句的基本格式

格式1:
#!/bin/bash
for WESTOS in $(seq 1 2 10)
do
        echo $WESTOS
done

显示1-10中的奇数：

#!/bin/bash
for NUM in `seq 1 2 10` 
do
 echo -n $NUM            ##-n不换行输出
 [  "$NUM" = "10" ] && exit
 sleep 1
 echo -ne "\r"           ##-e 处理特殊字符， \r 将光标移动至首行，但不换行
done

格式2:
#!/bin/bash
for WESTOS in westos linux lee
do
        echo $WESTOS
done

[root@westoslinux mnt]# vim test1.sh
#!/bin/bash
for NUM in 1 2 3 4
do
 echo -n $NUM            ##-n表示不换行输出
 [  "$NUM" = "4" ] && exit    ##当显示4的时候退出
 sleep 1
done

#!/bin/bash
for NUM in 1 2 3 4
do
 echo -n $NUM
 [  "$NUM" = "4" ] && exit
 sleep 1
 echo -ne "\r"           ##-e 处理特殊字符， \r 将光标移动至首行，但不换行
done

格式3:
#!/bin/bash
for WESTOS in {10..1}
do
        echo $WESTOS
done

#!/bin/bash
for NUM in {1..10}
do
 echo -n $NUM
 [  "$NUM" = "10" ] && exit
 sleep 1
 echo -ne "\r"           ##-e 处理特殊字符， \r 将光标移动至首行，但不换行
done

格式4:
#!/bin/bash
for ((WESTOS=0;WESTOS<10;WESTOS++ ))
do
        echo $WESTOS
done

vim test1.sh         ##显示数字从0到10，每隔一秒钟显示一次并清空之前的显示
#!/bin/bash
clear
for ((NUM=0;NUM<=10;NUM++))
do
 echo -n $NUM
 sleep 1               
 echo -ne "\r"
done

脚本练习1:​

check_host.sh
用此脚本检测10台与您当前主机直连主机是否网络通常
如果网络通常请显示主机的ip列表

[root@westoslinux mnt]# vim check_host.sh 
#!/bin/bash
for HOST in 172.25.254.{1..10}
do
  ping -c1 -w1 $HOST &> /dev/null &&{
  echo $HOST
  }
done
[root@westoslinux mnt]# sh check_host.sh 
172.25.254.10

 脚本练习2：

[root@westoslinux mnt]# vim user_create.sh 
#!/bin/bash
[ -z "$*" ] &&{
 echo "Please input userlist!!"      ##判断脚本之后是否为空
 exit
 } 
[ ! -e "$*"  ] &&{
  echo "$*  is not exist!!"         ##判断脚本之后跟得文件是否存在
  exit
 }
 for USER in `cat $*`
 do
  id $USER &> /dev/null &&{   ##userlist文件中的用户如果在系统中存在就不建立，如果不存在建立用户
   echo "$USER is exist"
  }||{
   useradd $USER
   echo "$USER is created!!"  
  }
 done

 

 脚本练习3：

[root@westoslinux mnt]# vim user_create.sh 
#!/bin/bash
[ -z "$1" ] &&{
  echo "Please input userlist!!"
  exit
}
[ -z "$2" ] &&{
  echo "Please input passwdfile!!"
  exit
}

Line_Num=`sed -n $= $1`
for LINE in `seq 1 $Line_Num`
do
  USERNAME=`sed -n ${LINE}p $1`
  PASSWORD=`sed -n ${LINE}p $2`
   id $USERNAME &> /dev/null &&{
      echo $USERNAME is exit
   }||{
      useradd $USERNAME
      echo $PASSWORD | passwd --stdin $USERNAME &> /dev/null && {
        echo $USERNAME is created!!
      }
   }
done

 二.条件语句

while...do语句

作用：条件为真执行动作
语句结构：
while ture  <!--条件为真-->
do                    <!--条件成立所作循环动作-->
done                <!--结束-->

[root@westoslinux mnt]# vim test3.sh
#!/bin/bash
for i in {1..5}
do
  while [ "$i" = "5" ]
  do
    read -p "Please input word:" WORD
    echo $WORD
  done
  echo $i
done

 until...do 语句

作用：条件为假执行动作
语句结构：
until false      <!--条件为假-->
do        <!--条件不成立所作循环动作-->
done         <!--结束-->

[root@westoslinux mnt]# vim test3.sh
#!/bin/bash
for i in {1..5}
do
  until [ "$i" != "5" ]
  do
    read -p "Please input word:" WORD
    echo $WORD
  done
  echo $i
done

if...then...elif...then...else...fi 语句

 作用:多次判定条件执行动作

代码结构：

if      <!--首次判断定-->
then    <!--条件成立执行动作-->
elif    <!--当首次判定不成立时再次判定-->
then    <!--条件成立执行动作-->
...     <!--elif可以书写多次-->
else    <!--所有条件不成立执行动作-->
fi        <!--结束-->

[root@westoslinux mnt]# vim test3.sh
#!/bin/bash
while true
do
  read -p "Please input filename for check:" FILE
  if [ "$FILE" = "exit" ]
  then
     exit
  elif [ ! -e "$FILE" ] 
  then
    echo $FILE is not exist
  elif [ -L "$FILE" ]
  then
     echo $FILE is link file
  elif [ -f "$FILE" ] 
  then
    echo $FILE is common file
  elif [ -d "$FILE" ]
  then
    echo $FILE is directory
  fi
done

  脚本练习

check_file.sh
please input filename: file
file is not exist
file is file
file is direcory
此脚本会一直询问直到用户输入exit为止

[root@westos139 mnt]# vim check_file.sh
#!/bin/bash
while true
do
  read -p "Please input filemane for check:" FILE
  if [ "$FILE" = "exit" ]
  then
      echo bye
      exit
  elif [ ! -e "$FILE" ]
  then
    echo "$FILE is not exist"
  elif [ -d "$FILE" ]
  then
     echo "$FILE is a directory"
  elif [ -f "$FILE" ]
  then
     echo "$FILE is a regular file"
  elif [ -S "$FILE" ]
  then
      echo "$FILE is socket"
  fi
done

 三.case

case $1 in
        word1|WORD1)
        action1
        ;;
        word2|WORD2)
        action2
        ;;
        *)
        action3
esac

[root@westos139 mnt]# vim case.sh 
#!/bin/bash
case $1 in
  westos|WESTOS)
  echo linux
  ;;
  linux|LINUX)
  echo westos
  ;;
  *)
  echo error
esac

脚本练习：

 create_user.sh add

输入用户名，如果存在显示用户已存在并继续输入用户名，如果不存在，显示输入密码，创建用户输入exit退出。

create_user.sh del

输入用户名，如果存在则删除用户。如果不存在则显示用户不存在并再次要求输入用户名。

[root@westos139 mnt]# vim create_user.sh
#!/bin/bash
USERCMD()
{
  read -p "please input username: " USERNAME
  if [ "$USERNAME" = "exit" ]
  then
    exit
  fi
}

case $* in
  add|ADD|Add)
  while true
  do
    USERCMD
    id $USERNAME &> /dev/null && {
      echo "$USERNAME is exist"
    }||{
      read -p "please input password: " -s PASSWORD
      useradd $USERNAME
      echo $PASSWORD|passwd --stdin $USERNAME &> /dev/null &&{
        echo ""
        echo "$USERNAME is created"
      }
    }
  done
  ;;
  del|DEL|Del)
  while true
   do
     USERCMD
     id $USERNAME &> /dev/null && {
       userdel -r $USERNAME
       echo "$USERNAME is deleted"
     }||{
        echo $USERNAME is not exist
     }
   done
   ;;
  *)
  echo "Please input add|del for following $0"
esac

 四.expect

[root@westos139 mnt]# vim ask.sh 
#!/bin/bash
read -p "what's your name: " NAME
read -p "HOw old are you: " AGE
read -p "Which objective you study: " OBJ
read -p "Are you happy?" FEEL
echo $NAME is $AGE\'s old study $OBJ feel $FEEL
[root@westos139 mnt]# vim answer.sh 
/mnt/ask.sh <<EOF
gyy
20
linux
happy
EOF

[root@westos139 mnt]# dnf install expect -y
[root@westos139 mnt]# vim ask.sh  ##问题脚本
#!/bin/bash
read -p "what's your name: " NAME
read -p "HOw old are you: " AGE
read -p "Which objective you study: " OBJ
read -p "Are you happy?" FEEL
echo $NAME is $AGE\'s old study $OBJ feel $FEEL
[root@westos139 mnt]# vim answer.exp ##应答脚本
#!/bin/expect
set timeout 3
set NAME [ lindex $argv 0 ]
set AGE  [ lindex $argv 1 ]
set OBJ  [ lindex $argv 2 ] 
set FEEL [ lindex $argv 3 ]
spawn /mnt/ask.sh
expect {
  “name” { send "$NAME\r";exp_continue }
  “old” { send "$AGE\r";exp_continue }
  “objective” { send "$OBJ\r";exp_continue }
  “happy” { send "$FEEL\r";exp_continue }
}
expect eof

[root@westos139 mnt]# vim answer.sh
/usr/bin/expect  <<EOF
spawn /mnt/ask.sh
expect {
"name" { send "$1\r";exp_continue }
"old" { send "$2\r";exp_continue }
"objective" { send "$3\r";exp_continue }
"happy" { send "$4\r"}
}
expect eof
EOF

 脚本练习

host_list.sh
检测172.25.254.1-172.25.254.10网络是否开启
如果网络正常请生成解析列表hosts_list

格式如下
ip           主机名称
例如:172.25.254.1为开启状态主机名为westos_student1.westos.org
hosts_list中
172.25.254.1           westos_student1.westos.org

[root@westos139 mnt]# vim host_list.sh 
#!/bin/bash
AUTO_SSH()
{
/usr/bin/expect <<EOF
spawn ssh -l root $1 hostname
expect {
"yes/no" {send "yes\r";exp_continue}
"password" {send "westos\r"}
}
expect eof
EOF
}
if [ -e "host_list" ] 
then
  echo host_list is exist
else
  for HOST in {1..10}
  do
    ping -c1 -w1 172.25.254.$HOST &> /dev/null &&{
      HOST_NAME=`AUTO_SSH 172.25.254.$HOST | tail -n 1`
      echo -e "172.25.254.$HOST\t$HOST_NAME" >> host_list
      }
  done
fi

五.break,continue,exit

continue          ##终止当此次前循环提前进入下个循环
break                ##终止当前所在语句所有动作进行语句外的其他动作
exit                     ##脚本退出

[root@westos139 mnt]# vim westos.sh 
#!/bin/bash
for NUM in {1..10}
do
  if [ "$NUM" = "5" ] 
  then
    echo luck number
    continue
  fi
    echo $NUM
done
echo end