bash while/until循环学习

while循环:条件满足,则循环;失败,则退出

如何退出?

必须有时刻,条件测试不成功

? :条件控制变量

while 条件测试:do

循环体

done

until循环;条件不满足,则循环;否则,退出

until 测试条件;do

循环体

done

bash编程之组合测试条件

逻辑与:多个条件同时满足

[ CONDITION1 ] && [ CONDITION2 ]

[ CONDITION1 -a CONDITION2 ]

[[ CONDITION1 && CONDITION2 ]]

注意:前两个使用单双中括号都可,但&&不允许用于单个中括号中,所有第三者只能用于双中括号中

逻辑或:多个条件满足一个

[ CONDITION1 ] || [ CONDITION2 ]

[ CONDITION1 -o CONDITION2 ]

[[ CONDITION1 || CONDITION2 ]]

注意 || 不允许出现在单中括号中

得摩根定律

!(条件1或者 条件2) = !条件1 并且!条件2

!(条件1且条件2)=!条件1 或者 !条件2

练习:

1.:通过键盘提示用户输入字符,将用户输入的小写字母转换为大写,转换一次之后,在此提醒,再输入再转换,直到输入quit退出;

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#! /bin/bash
#
 
read -p -t 5 "Enter a Word: " word
 
while [[ "$word" != "quit" ]]; do
  echo $word | tr 'a-z' 'A-Z'
  read -p -t 5 "Enter a Word again: " word
done

2.写一个脚本,实现如下功能;

1、显示如下菜单:

CPU) show cpu info;

men) show memory info;

disk) show disk info;

quit) quit

Enter your option:

2、根据用户的选择输出相应信息,每次执行后,不退出,而由用户咋此指定新的选项

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#! /bin/bash
#
cat <<EOF
    cpu) print cpu infomation
    men) print memory infomation
    disk) print disk infomation    
    quit) Quit
EOF
 
read -p "Enter your option: " option
option=`echo $option | tr 'a-z' 'A-Z'`
 
while [[ "$option" != "QUIT" ]]; do
  if [[ "$option" == "CPU" ]]; then
    cat /proc/cpuinfo
  elif [[ "$option" == "MEM" ]]; then
    free -m
  elif [[ "$option" == "DISK" ]]; then
    df -Th
  else
    echo "Wrong Option..."
  fi
   
  read -p "Enter your option: " option
  option=`echo $option | tr 'a-z' 'A-Z'`
done

3.提示用户输入一个用户名,显示用户名UID和SHELl信息,否则,则显示无此用户,显示完成后,提示用户再次输入,如果quit则退出;

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#! /bin/bash
#
cat <<EOF
  Username)Enter your Username..
  quit)quit..
EOF
 
read -p "Enter Your userName: " userName
userName=`echo $userName | tr 'A-Z' 'a-z'`
 
while [[ "$userName" != "QUIT" ]]; do
  sysUser=`cat /etc/passwd | grep  ^$userName | cut -d: -f1 | tr 'A-Z' 'a-z'`
  if [[ "$userName" == "$sysUser" ]]; then
    echo "This $userName `cat /etc/passwd | grep -i ^$userName | cut -d: -f3,7`"
  else
    echo "No Such $userName.."
  fi
  read -p "Enter Your userName: " userName
  userName=`echo $userName | tr 'A-Z' 'a-z'`
done
 
#! /bin/bash
#
 
read -t 2 -p "Enter a user name: " userName
userName=`echo $userName | tr 'A-Z' 'a-z'`
UID=`grep "^$userName\>" /etc/passwd | cut -d: -f3`
SH=`grep "^$userName\>" /etc/passwd | cut -d: -f7`
 
while [[ "$userName" != "quit" ]]; do
  if [ -z "$userName" ]; then
    echo "Username null...."
  elif id $userName &> /dev/null; then
    echo "$userName uid: $UID"
    echo "$userName Shell: $SH"
  else
    echo "No such user...."
  fi
  read -t 2 -p "Enter a user name again(quit to exit) " userName
done

4.求100以内所有正整数的和;

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#! /bin/bash
#
declare -i sum=0
declare -i i=1
 
while [ $i -le 100 ];do
    let sum+=$i
    let i++
done
echo $sum
 
#! /bin/bash
#
declare -i sum=0
declare -i i=1
 
until [ $i -gt 100 ]; do
        let sum+=$i
        let i++
done
 
echo $sum

5.求100以内所有偶数之和;

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#! /bin/bash
#
 
declare -i evensum=0
declare -i i=1
 
while [ $i -le 100 ]; do
  if [ $[$i%2] -eq 0 ]; then
    let evensum+=$i
  fi
  let i++
done
echo $evensum
 
#! /bin/bash
#
 
declare -i sum=0
declare -i i=0
 
while [[ $i -le 100 ]]; do
  let sum+=$i
  let i+=2
done
 
echo $sum

6.用until求100以内整数之和;

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

7.提供一个用户名,判断用户是否登陆当前系统;

1.如果没有登陆,则停止5秒之后再次判断,直到用户登录系统,显示用户登录,而后退出

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  #! /bin/bash
  #
  read -t 5 -p "Enter Your userName: " userName
  userName=`echo $userName | tr 'A-Z' 'a-z'`
 
  who | grep "$userName" &> /dev/null
  retVal=$?
 
  while [ $retVal -ne 0 ]; do
    sleep 5
    read -t 5 -p "Enter Your userName: " userName
    userName=`echo $userName | tr 'A-Z' 'a-z'`
  done
  echo "Welcome $userName login System..."
 
  #! /bin/bash
  #
  read -t 5 -p "Enter Your userName: " userName
 
  while ! id $userName &> /dev/null; do
    read -t 5 -p "Enter Your userName: " userName
  done
 
  who | grep "^$userName" &> /dev/null
  retVal=$?
 
  while [ $retVal -ne 0 ]; do
    sleep 5
    who | grep "$userName" &> /dev/null
    retVal=$?
  done
  echo "Welcome $userName login System..."
 
  #! /bin/bash
  #
  read -t 5 -p "Enter Your userName: " userName
 
  while ! id $userName &> /dev/null; do
    read -t 5 -p "Enter Your userName again: " userName
  done
 
  while ! who | grep "^$userName" &> /dev/null; do
    sleep 5
  done
  echo "Welcome $userName login System..."
 
  #! /bin/bash
#
read -t 5 -p "Enter Your userName: " userName
 
until [ -n "$userName" ] && id $userName &> /dev/null ; do
  read -t 5 -p "Enter Your userName again: " userName
done
 
until who | grep "^$userName" &> /dev/null; do
  sleep 5
done
echo "Welcome $userName login System..."

8.取出当前系统上,默认shell为bash的用户;

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#! /bin/bash
#
while read line; do
  [[ `echo $line | cut -d: -f7` == "/bin/bash" ]] && echo $line | cut -d: -f1
done < /etc/passwd

9.显示其ID号为偶数的用户;

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#! /bin/bash
#
while read line; do
  userID=`echo $line | cut -d: -f3`
  if [ $[$userID%2] -eq 0 ]; then
    echo -n "$userID: "
    echo $line | cut -d: -f1
  fi
done < /etc/passwd

10.显示/etc/rc.d/rc.sysinit文件中,其总字符个数大于30的行;

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#! /bin/bash
#
while read line; do
  charCounts=`echo $line | wc -c`
  if [ $charCounts -gt 30 ]; then
    echo -n "$charCounts: "
    echo $line
  fi
done < /etc/rc.d/rc.sysinit

11.显示用户其UID和GID均为偶数的用户;

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#! /bin/bash
#
while read line; do
  userID=`echo $line | cut -d: -f3`
  groupID`echo $line | cut -d: -f4`
  if [ $[$userID%2] -eq 0 -a $[$groupID%2] -eq 0 ]; then
    echo -n "$userID,$groupID: "
    echo $line | cut -d: -f1
  fi
done < /etc/passwd

12.显示/etc/rc.d/rc.sysinit文件中,其总字符个数大于30且以非#开头的行;

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#! /bin/bash
#
while read line; do
  charCounts=`echo $line | wc -c`
  if [ $charCounts -gt 30 ] && [["$line" =~ ^[^#] ]]; then
    echo -n "$charCounts: "
    echo $line
  fi
done < /etc/rc.d/rc.sysinit

13.写一个脚本,完成如下任务;

1.提示用户输入一个磁盘设备文件路径不存在或不是一个块设备,则提示用户重新输入,知道输入正确为止,或者输入quit以9为退出码结束脚本

2.提示用户"下面的操作会清空磁盘的数据,并提问是否继续"

如果用户给出字符y或yes,则继续,否则,则提供以8为退出码结束脚本

3.将用户指定的磁盘上的分区清空,而后创建两个分区,大小分别为100M和512M

4.格式化这两个分区

5.将第一个分区挂载至/mnt/boot目录,第二个分区挂载至/mnt/sysroot目录

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