shell脚本-for循环语句详解
shell循环-for
for循环默认跳过空行，遇到空行或者空格则不会去理睬
循环分为循环次数是固定的和循环次数不是固定的，固定的有for循环，不固定的有while和until循环
for循环每次都以空格进行分隔，例如 lisi 123，本应该让i变量取一整行，结果却把lisi，123分别赋给了变量，达不到我们预期的效果，即使使用awk命令也同样只会输出lisi，123，因为$2不存在，详细请看036视频中的28分处，可以修改IFS分隔符值，让for处理文件时按回车分隔
IFS：内部字段分隔符
例如修改IFS分隔符为回车，IFS=$’\n’或者IFS’'引号中间必须有回车，否侧会处理失败
break与continue的区别
break是跳出循环
continue是跳出本次循环
1.for语法结构
shell：
for 变量名 in 取值列表
do
循环体
done
C语言风格：
for ((初值;条件;步长))
do
循环体
done
for循环的特殊用法
#!/bin/bash
for i
do
let $sum=$sum+$i
done
执行./for.sh 1 2
输出3
for i后面不加东西相当于for i in $*也就是所有参数
1.1批量添加网卡接口
for i in {2..20}
do
ifconfig ens33:$i 192.168.81.$i
done
1.2for实现批量主机ping探测
循环体中的{}&表示将循环体中的命令放到后台执行
wait命令：后台程序运行完后再执行后面的命令
#!/bin/bash
#-------------------实现批量主机ping探测--------------
#20200208
>ip.txt
for i in {2..254}
do
{
ip=192.168.81.$i
ping -c1 -W1 $ip &>/dev/null
if [ $? -eq 0 ];then
echo $ip | tee -a ip.txt
fi
}&
done
wait
echo "finish........."
1.3从文件中获取ip地址进行探测
for ip in $(cat ip.txt)
do
ping -c1 -W1 $ip &>/dev/null
if [ $? -eq 0 ];then
echo "$ip is up..."
else
echo "$ip is down..."
fi
done
1.4for实现批量用户创建
#!/bin/bash
#------------实现批量用户-------------------
#20200208
while :
do
echo -en "\e[35m Please enter user prefix & user password & user numbers [zhangsan 123 10]: \e[0m"
read prefix password numbers
printf "user infomation:
-----------------------------------------------
userprefix: $prefix
userpassword: $password
usernumbers: $numbers
-----------------------------------------------
"
read -p "Aree you sure create user[y|n|q]: " action
case $action in
y|Y)
break
;;
q)
exit
;;
esac
done
for i in $(seq -w $numbers)
do
user=$prefix$i
id $user &>/dev/null
if [ $? -eq 0 ];then
echo "user $user already exists..."
else
useradd $user
echo "$password" |passwd --stdin $user &>/dev/null
if id $user &>/dev/null;then
echo "user is created....."
fi
fi
done
1.5实现从文件中批量创建用户
#!/bin/bash
#------------------实现文件中批量创建用户-----------------
#20200209
if [ $# -eq 0 ];then
echo "usage: $(basename $0) file"
exit 1
fi
if [ ! -f $1 ];then
echo "error file"
exit 2
fi
IFS=$'\n'
for line in `cat $1`
do
user=$(echo "$line" | awk '{print $1}')
pass=$(echo "$line" | awk '{print $2}')
id $line &>/dev/null
if [ $? -eq 0 ];then
echo "$i is already exists..."
else
useradd $user
echo "$pass" |passwd --stdin $user &>/dev/null
if [ $? -eq 0 ];then
echo "$i is created..."
fi
fi
done
1.6批量创建用户改版
对比1.5主要有一下改进
1.如果用户什么都不输入则重新走一遍循环
2.如果用户输入的numbers不是整数则重新循环，并提示参数设置的不对
3.如果用户只输入了用户前缀则也重新循环
#!/bin/bash
while :
do
echo -en "\e[36m please enter userprefix & userpassword & usernumbers: \e[0m"
read userprefix userpassword usernumbers
cat <<-EOF
----------------------------------------------------------------------------
user information
userprefix: $userprefix
userpassword: $userpassword
usernumbers: $usernumbers
----------------------------------------------------------------------------
EOF
if [[ ! "$usernumbers" =~ ^[0-9]+$ ]] && [ -z "$3" ];then
echo -e "\e[31m error parameter\e[0m"
echo -e "\e[33mPlease input again\e[0m"
continue
fi
read -p "Are you sure user information[y|n|q]: " action
case $action in
y|Y)
break
;;
q)
exit 1
esac
done
for i in $(seq -w $usernumbers)
do
user=$userprefix$i
id $user &>/dev/null
if [ $? -eq 0 ];then
echo -e "\e[31m user $user already exists... \e[0m"
else
useradd $user
echo "$userpassword" | passwd --stdin $user &>/dev/null
if [ $? -eq 0 ];then
echo -e "\e[32m $user is created....\e[0m"
fi
fi
done
1.7根据模式进行批量用户创建和删除
1.让用户输入用户名前缀、密码、数量
2.$3必须是整数
3.将用户输入的信息打印成菜单
4.询问用户是否确认创建/删除
5.创建完成提示创建/删除成功
6.循环，用户输入的不正常则重新输入
7.如果创建则执行函数创建，删除则执行函数删除
#!/bin/bash
qrxx(){
if [[ ! $usernumbers =~ ^[0-9]+$ ]];then
echo -e "\e[31merror parameter\e[0m"
continue
fi
cat <<-EOF
+---------------------------------------------------------+
user information
userprefix: $userprefix
userpass: $userpass
usernumbers: $usernumbers
+---------------------------------------------------------+
EOF
}
create(){
echo -en "\e[034mplease enter userprefix userpass usernumbers[ user 123 10 ]: \e[0m"
read userprefix userpass usernumbers
qrxx
echo -en "\e[35mare you sure create user infomation [y|n] \e[0m"
read action
case $action in
y|Y)
for i in `seq -w $usernumbers`
do
user=$userprefix$i
id $user &>/dev/null
if [ $? -ne 0 ];then
useradd $user
echo "$userpass" |passwd --stdin $user &>/dev/null
if [ $? -eq 0 ];then
echo "$user is created..."
fi
else
echo "$user already exists..."
fi
done
;;
n|N)
continue
;;
*)
echo "error action,please input [y|n]."
esac
#echo "Parameter is not complete"
}
delete(){
echo -en "\e[034mplease enter userprefix usernumbers[ user 10 ]: \e[0m"
read userprefix usernumbers
qrxx
echo -en "\e[35mare you sure delete user information [y|n]: \e[0m"
read action
case $action in
y|Y)
for i in $(seq -w $usernumbers)
do
user=$userprefix$i
id $user &>/dev/null
if [ $? -eq 0 ];then
userdel -r $user
if [ $? -eq 0 ];then
echo "$user is deleted..."
fi
else
echo "$user is not exists... "
fi
done
;;
n|N)
continue
esac
}
while :
do
cat <<-EOF
+---------------------------------------------------------+
| MENU |
| 1.Batch to create user |
| 2.Batch delete user |
| q.exit |
+---------------------------------------------------------+
EOF
echo -en "\e[33mPlease input you want to choose the mode: \e[0m"
read mode
case $mode in
1)
create
;;
2)
delete
;;
q)
exit
;;
*)
echo "error"
esac
done