loop

while do done, until do done

语法

while [ condition ]  <==中括号内的状态就是判断式
do            <==do 是回圈的开始！
    程序段落
done          <==done 是回圈的结束

用例

[root@www scripts]# vi sh13.sh
#!/bin/bash
# Program:
#    Repeat question until user input correct answer.
# History:
# 2005/08/29    VBird    First release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH

while [ "$yn" != "yes" -a "$yn" != "YES" ]
do
    read -p "Please input yes/YES to stop this program: " yn
done
echo "OK! you input the correct answer."

for...do...done

用法

for var in con1 con2 con3 ...
do
    程序段
done

用例一：

[root@www scripts]# vi sh15.sh
#!/bin/bash
# Program:
#     Using for .... loop to print 3 animals
# History:
# 2005/08/29    VBird    First release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH

for animal in dog cat elephant
do
    echo "There are ${animal}s.... "
done

用例二：

[root@www scripts]# vi sh16.sh
#!/bin/bash
# Program
#       Use id, finger command to check system account's information.
# History
# 2009/02/18    VBird   first release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH
users=$(cut -d ':' -f1 /etc/passwd)  # 撷取帐号名称
for username in $users               # 开始回圈进行！
do
        id $username
        finger $username
done

for...do...done 的数值处理

用法

for (( 初始值; 限制值; 运行步阶 ))
do
    程序段
done

用例：

[root@www scripts]# vi sh19.sh
#!/bin/bash
# Program:
#     Try do calculate 1+2+....+${your_input}
# History:
# 2005/08/29    VBird    First release
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin:~/bin
export PATH

read -p "Please input a number, I will count for 1+2+...+your_input: " nu

s=0
for (( i=1; i<=$nu; i=i+1 ))
do
    s=$(($s+$i))
done
echo "The result of '1+2+3+...+$nu' is ==> $s"