shell循环结构之for循环

for循环

语法：

1)

for 变量 in 取值列表; do
statement
statement
done

2)

for 变量 in 取值列表
do
statement
statement
done

取值列表：
数字
10 20 30
使用seq命令生成数字的序列
seq 10
seq 3 10
seq 1 2 10
字符
aa bb cc

文件

编写脚本，计算1---100的和

#!/bin/bash
#

sum=0

for i in `seq 100`; do
let sum=$sum+$i
done

echo $sum

编写脚本，计算1--100所有奇数的和

#!/bin/bash
#

sum=0

for i in `seq 100`; do
let ys=$i%2
if [ $ys -ne 0 ]; then
let sum=$sum+$i
fi
done

echo $sum

编写脚本，实现批量创建用户user1...user10

#!/bin/bash
#

for i in `seq 10`; do
if ! id user$i &> /dev/null; then
useradd user$i
echo "redhat" | passwd --stdin user$i &> /dev/null
echo "用户user$i创建完成，初始密码为redhat"
else
echo "用户user$i已经存在"
fi
done

编写脚本，检测172.16.20.0/24在线主机IP

#!/bin/bash
#

network=172.16.20.

for i in `seq 254`; do
if ping -c 1 -W 1 $network$i &> /dev/null; then
echo "Host $network$i is up"
fi
done

启动多线程：

#!/bin/bash
#

network=172.16.80.

for i in `seq 254`; do
{
if ping -c 1 -W 1 $network$i &> /dev/null; then
echo "Host $network$i is up"
fi
}&
done
wait

以字符作为取值列表

#!/bin/bash
#

for name in alice natsha kira merry; do
useradd $name
echo "$name create finished."
done

以文件作为取值列表

`cat FILE`

编写脚本，向系统中所有用户打招呼

#!/bin/bash
#

for i in `awk -F: '{print $1}' /etc/passwd`; do
echo "Hello, $i"
done

编写脚本， 将某目录下所有以.txt结尾的文件改为以.mp3结尾

#!/bin/bash
#

for i in `ls -l /tmp/test | grep "txt$" | awk '{print $9}'`; do
file_name=`echo $i | awk -F. '{print $1}'`
mv /tmp/test/$i /tmp/test/$file_name.mp3
done

编写脚本, 分别统计/bin/bash和/sbin/nologin用户的个数

#!/bin/bash
#

bash_number=0
nologin_number=0

line=$(wc -l /etc/passwd | awk '{print $1}')

for i in `seq $line`; do
sh_name=$(head -n $i /etc/passwd | tail -1 | awk -F: '{print $7}')
case $sh_name in
/sbin/nologin)
let nologin_number=$nologin_number+1
;;
/bin/bash)
let bash_number=$bash_number+1
;;
esac
done

echo "shell为/bin/bash的：$bash_number"
echo "shell为/sbin/nologin的：$nologin_number"

编写脚本，显示九九乘法表

#!/bin/bash

#for嵌套for循环

#9*9乘法口诀

echo "for的九九乘法表"

for(( i=1 ;i<=9;i++ ))

do

for(( j=1;j<=9;j++ ))

do

#当$j小于等于$i,在屏幕上打印乘法表

[ $j -le $i ] && echo -n "$i*$j=$[ $i * $j ] "

done

echo ''

done

中断循环的语句
break 中断整体循环
continue 中断本次循环

break用法：

#!/bin/bash
#

sum=0

for i in `seq 100`; do
let sum=$sum+$i
if [ $sum -ge 3000 ]; then
echo $i
break
fi
done

continue用法：

#!/bin/bash
#

sum=0

for i in `seq 100`; do
let ys=$i%2
if [ $ys -eq 0 ]; then
continue
fi
let sum=$sum+$i
done

echo $sum

编写脚本，列出系统中shell为/bin/bash的前5个用户名

#!/bin/bash
#

number=0
line=$(wc -l /etc/passwd | awk '{print $1}')

for i in `seq $line`; do
sh_name=`head -n $i /etc/passwd | tail -1 | awk -F: '{print $7}'`
if [ $sh_name == "/bin/bash" ]; then
name=`head -n $i /etc/passwd | tail -1 | awk -F: '{print $1}'`
echo -n "$name "
let number=$number+1
if [ $number -eq 5 ]; then
break
fi
fi
done
echo