while语法格式

while 测试条件 do 指令 done

while循环可用于读取键盘信息。下面的例子中，输入信息被设置为变量FILM，按<Ctrl-D>结束循环。

echo '按下 <CTRL-D> 退出' echo -n '输入你最喜欢的网站名: ' while read FILM do echo "是的！$FILM 是一个好网站" done

#!/bin/bash int=1 while(( $int<=5 )) do echo $int let "int++" done

实例 1

!/bin/bash

#$RANDOM是一个系统随机数的环境变量 num=$((RANDOM%100)) while : do read -p "Please guess my number [0-99]: " number echo $num if [ $number -lt $num ] then echo "$number小于$num" elif [ $number -gt $num ] then echo "$number大于$num" elif ((number==num)) then echo "$number等于num" break fi done 执行结果 [root@localhost shell]# sh where1.sh Please guess my number [0-99]: 24 56 24小于56 Please guess my number [0-99]: 89 56 89大于56 Please guess my number [0-99]: 56 56 56等于num

实例 2

#!/bin/bash

file=/etc/resolv.conf while read -r line #while IFS=: read -r line abc do echo $line done < "$file"

while IFS=: read -r user enpass uid gid desc home shell do [ $uid -ge 500 ] && echo "User $user $enpass ($uid) $gid $desc $home $shell" done < /etc/passwd

执行结果

[root@localhost shell]# sh while2.sh ; generated by /usr/sbin/dhclient-script search localdomain nameserver 192.168.1.1 User polkitd x (999) 998 User for polkitd / /sbin/nologin User chrony x (998) 996 /var/lib/chrony /sbin/nologin User www x (1000) 1000 /home/www /sbin/nologin User saslauth x (996) 76 Saslauthd user /run/saslauthd /sbin/nologin User mysql x (1001) 1001 /home/mysql /sbin/nologin User zabbix x (1002) 1002 /home/zabbix /sbin/nologin User user1 x (1003) 1003 /home/user1 /bin/bash User user2 x (1004) 1004 /home/user2 /bin/bash User user3 x (1005) 1005 /home/user3 /bin/bash User user4 x (1006) 1006 /home/user4 /bin/bash User user5 x (1007) 1007 /home/user5 /bin/bash

实例 3

#!/bin/bash count=1 while [ $count -lt 10 ] do let "count+=1" echo $count done

i=0 while (( i !=1 )) do if [[ $@ = ok ]] then i=1 fi done

执行结果

[root@localhost shell]# sh while3.sh ok 2 3 4 5 6 7 8 9 10

无限循环语法格式：

while : do command done 或者

while true do command done 或者

for (( ; ; ))

**实例 4 **

#!/bin/bash

#whie--case...esac while true do echo "What is your preferred scripting language?" echo "1) bash" echo "2) prel" echo "3) python" echo "4) ruby" echo "5) I do not know !" read -p "Pls input num: " lang case $lang in 1) echo "you selected bash" ;; 2) echo "you selected prel" ;; 3) echo "you selected python" ;; 4) echo "you selected ruby" ;; 5) echo "I do not know!" exit ;; esac done

执行结果

root@localhost shell]# sh while-select.sh What is your preferred scripting language?

  1. bash
  2. prel
  3. python
  4. ruby
  5. I do not know ! Pls input num: 1 you selected bash What is your preferred scripting language?
  6. bash
  7. prel
  8. python
  9. ruby
  10. I do not know !