⑤.shell 循环while

语法示例:

while 条件为真
do
   echo ok
done


#!/bin/bash
while true
do
   echo ok
done

while循环数字

#!/bin/bash
a=1
b=9
while [ $a -lt 10 ]
do
   sum=$((a + b))
   echo $a + $b = $sum
   let a++
   let b--
done 

while 逐行读取 根据文件创建用户

准备用户文件
[root@RainGod ~]# cat user.txt 
yt01:test1
yt02:test2
yt03:test3


脚本
#!/bin/bash
while read line 
do
   user=`echo $line|awk -F: '{print $1}'`
   passwd=`echo $line|awk -F: '{print $2}'`
   id  $user &>/dev/null
   if [ $? -eq 0 ];then
      echo "$user is exiting"
   else
      useradd $user &>/dev/null
      echo $passwd |passwd --stdin $user
      echo "$user create ok"
   fi
done<user.txt

continue 终止本次循环 继续从头循环

#!/bin/bash
a=1
while [ $a -lt 100 ]
do
    if [ $a -eq 50 ];then
         echo 'eq 50 '
          let a++
          continue
    fi
    echo $a
   let a++
done 

break 跳出while循环 继续执行下面的语句

#!/bin/bash
a=1
while [ $a -lt 100 ]
do
    if [ $a -eq 50 ];then
         echo 'eq 50 '
          let a++
          break          
    fi
    echo $a
   let a++
done 
echo 'test'

exit 结束脚本

#!/bin/bash
a=1
while [ $a -lt 100 ]
do
    if [ $a -eq 50 ];then
         echo 'eq 50 '
          let a++
          exit
    fi
    echo $a
   let a++
done 
echo 'test'