（八）for语句

（1）语法

（2）批量ping主机

这里有个重点就是把每次ping主机的动作放到后台运行

#!/bin/bash
>ip.txt
for i in {1..254}
do 
	ip=192.168.111.$i
	{
	ping -c1 -W1 $ip &>/dev/null 
	if [ $? -eq 0 ];then
		echo "$ip is up!" |  tee -a ip.txt
	fi
	}&
done
wait
echo "success"

（2）用户创建

重点：seq -w 10 会生成例如 01 02，前面使用0填充

#!/bin/bash
while true
do
	read -p "please input prefix password number[bob 123456 10]" prefix password number
	printf "user information:
	----------------------------------
	user prefix:$prefix
	user password:$password
	user number:$number
	----------------------------------
	"
	read -p "Are you sure?[y|n]" action
	if [ "$action" = y ];then
		break
	fi
done
for i in $(seq -w $number)
do
	user=$prefix$i
	id $user &>/dev/null
	if [ $? -eq 0 ];then
		echo "user $user is already exist!"
	else
		useradd $user
		echo "$password" | passwd --stdin $user &>/dev/null
		if [ $? -eq  0 ];then
			echo "user $user is created!"
		fi
	fi
done

（3）实现文件中批量创建用户

重点：默认for循环是根据空白或tab键进行分割，这样对文件进行for循环，例如文件内容(jack01 123) 会把这一行当成两行内容，解决方案：使用IFS变量重新定义分割符
IFS=$' '

#!/bin/bash

if [ $# -eq 0 ];then
	echo "Usage: $(basename $0) file"
	exit 1
fi 
if [ ! -f $1 ];then
	echo "error file!"
	exit 2
fi
#希望for处理文件按回车分隔,而不是空格或tab空格
#重新定义分割符
#IFS=$'
'
IFS=$'
'
for line in $(cat $1)
do
	user=$(echo $line |awk '{print $1}')
	pass=$(echo $line |awk '{print $2}')
	id $user &>/dev/null
	if [ $? -eq 0 ];then
		echo "user $user is already exists!"
	else
		useradd $user &>/dev/null
		echo "$pass" | passwd --stdin $user
		if [ $? -eq 0 ];then
			echo "$user is created!"
		fi
	fi
done

用户文件内容如下，第一列是用户名，第二列是用户密码

jack01 123
jack02 456
jack03 789