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文章目录
循环及并发数控制
for while until循环
语法结构
1. =======for循环======================
for 条件测试
do
循环体
done
=======当条件为真时，执行循环体=======
2. =======while循环===================
while 条件测试
do
循环体
done
========当条件为真时，执行循环体=======
3. =======until循环====================
until 条件测试
do
循环体
done
========当条件为假时，执行循环体=======
for循环并发删除用户
#!/usr/bin/bash
. /etc/init.d/functions
Prefix=lss
for i in `seq 10`
do
{
User=$Prefix$i
id $User &> /dev/null
if [ $? -eq 0 ];then
userdel -r $User && action "userdel $User" /bin/true
else
echo ""
action "NO $User" /bin/false
fi
}& #中间这段直接放到后台执行
done
wait #等前面放到后台的所有任务都执行完毕，在执行后面的
echo "END"
//测试删除lss1~lss10
[root@mysql-master /soft/scripts]# ./userdel.sh
NO lss10 [FAILED]
userdel lss6 [ OK ]
userdel lss7 [ OK ]
userdel lss3 [ OK ]
userdel lss4 [ OK ]
userdel lss8 [ OK ]
userdel lss9 [ OK ]
userdel lss1 [ OK ]
userdel lss5 [ OK ]
userdel lss2 [ OK ]
END
[root@mysql-master /soft/scripts]#
for在读取行获取参数时以空格为分隔符,while可将行作为分隔符
// for在读取行获取参数时以空格为分隔符
例如：文件user.txt
[root@mysql-master /soft/scripts]# cat user1.txt
lss1 123
lss2 1233
lss3 2345
#!/usr/bin/bash
#希望for处理文件按回车分隔，而不是空格或tab
#用IFS重新定义分隔符
#IFS内部字段分隔符
echo "用IFS处理前"
for line in `cat user1.txt`
do
user=`echo $line|awk '{print $1}'`
pass=`echo $line|awk '{print $2}'`
echo "User:$user Passwd:$pass"
done
echo "用IFS处理后"
IFS=$'\n'
for line in `cat user1.txt`
do
user=`echo $line|awk '{print $1}'`
pass=`echo $line|awk '{print $2}'`
echo "User:$user Passwd:$pass"
done
[root@mysql-master /soft/scripts]# ./fortest.sh
用IFS处理前
User:lss1 Passwd:
User:123 Passwd:
User:lss2 Passwd:
User:1233 Passwd:
User:lss3 Passwd:
User:2345 Passwd:
用IFS处理后
User:lss1 Passwd:123
User:lss2 Passwd:1233
User:lss3 Passwd:2345
[root@mysql-master /soft/scripts]#
- while比较适合处理文件，可直接获取到行
[root@mysql-master /soft/scripts]# vim batch_useradd4.sh
#!/usr/bin/bash
while read line
do
User=`echo $line|awk '{print $1}'`
Password=`echo $line|awk '{print $2}'`
id $User &>/dev/null
if [ $? -eq 0 ];then
echo "$User is already exists or Format error"
else
useradd $User && echo "$Password" |passwd --stdin $User &>/dev/null
if [ $? -eq 0 ];then
echo "$User is created"
fi
fi
done < /soft/scripts/user1.txt
//测试
[root@mysql-master /soft/scripts]# sh batch_useradd4.sh
lss1 is created
lss2 is created
is already exists or Format error
lss3 is created
[root@mysql-master /soft/scripts]#
并发控制（FD和命名管道实现并发）
- FD文件句柄
//通过exec 3<> ip2.txt 打开文件
//通过exec 3<&- 关闭文件(释放文件句柄)
//文件删除不要紧，只要文件没被关闭句柄还在，就依然可以将文件还原cp /proc/$$/fd/6 ip2.txt
//fd 文件句柄没有被释放，还可以cp回来
[root@mysql-master /soft/scripts]# exec 6<> ip2.txt #打开文件
[root@mysql-master /soft/scripts]# cat ip2.txt
192.168.1.4
...
[root@mysql-master /soft/scripts]# ll /proc/$$/fd
...
lrwx------ 1 root root 64 Oct 28 03:36 6 -> /soft/scripts/ip2.txt
[root@mysql-master /soft/scripts]# rm -f ip2.txt
[root@mysql-master /soft/scripts]# ll /proc/$$/fd
...
lrwx------ 1 root root 64 Oct 28 03:36 6 -> /soft/scripts/ip2.txt (deleted)
//通过文件句柄恢复文件
[root@mysql-master /soft/scripts]# ll /proc/$$/fd
...
lrwx------ 1 root root 64 Oct 28 03:36 6 -> /soft/scripts/ip2.txt (deleted)
[root@mysql-master /soft/scripts]# cp /proc/$$/fd/6 /soft/scripts/ip2.txt
[root@mysql-master /soft/scripts]# cat ip2.txt
192.168.1.4
...
//关闭文件句柄
[root@mysql-master /soft/scripts]# exec 6<&- #关闭文件
[root@mysql-master /soft/scripts]# ll /proc/$$/fd #文件句柄被释放
total 0
lrwx------ 1 root root 64 Oct 28 03:36 0 -> /dev/pts/1
lrwx------ 1 root root 64 Oct 28 03:36 1 -> /dev/pts/1
lrwx------ 1 root root 64 Oct 28 03:36 2 -> /dev/pts/1
lrwx------ 1 root root 64 Oct 28 05:13 255 -> /dev/pts/1
[root@mysql-master /soft/scripts]#
- 命名管道
//创建命名管道
[root@mysql-master /soft/scripts]# mkfifo /tmp/tmpfifio
//测试
//先在1终端准备接受管道放入的命令
[root@mysql-master /soft/scripts]# tty
/dev/pts/1
[root@mysql-master /soft/scripts]# grep yum /tmp/tmpfifio
//然后在0终端放入rpm -qa命令到/tmp/tmpfifio管道中
[root@mysql-master /soft/scripts]#
[root@mysql-master /soft/scripts]# tty
/dev/pts/0
[root@mysql-master /soft/scripts]# rpm -qa > /tmp/tmpfifio #回车后1终端局可以拿到命令，最后管道变成空了
// /dev/pts/1
[root@mysql-master /soft/scripts]# grep yum /tmp/tmpfifio
yum-plugin-fastestmirror-1.1.31-45.el7.noarch
yum-metadata-parser-1.1.4-10.el7.x86_64
yum-3.4.3-158.el7.centos.noarch
[root@mysql-master /soft/scripts]#
- 案例：FD和命名管道实现并发数控制
[root@mysql-master /soft/scripts]# vim thread_ping.sh
#最大并发数
Thread_num=5
#命名管道文件
Tmp_fifo=/tmp/$$.fifo
#创建命名管道文件
mkfifo $Tmp_fifo
#用文件句柄(随便给个6)打开管道文件
exec 6<> $Tmp_fifo
rm -f $Tmp_fifo
##控制并发数
for i in `seq $Thread_num`
do
#向管道中放入最大并发数个行，供下面read读取
echo >&6
done
##
IP=192.168.1
for i in {1..254}
do
#通过文件句柄读取行，当行取尽时，停止下一步（并发）
read -u 6
{
ping -c1 -W1 $IP.$i &>/dev/null
if [ $? -eq 0 ];then
echo "$IP.$i is UP"
else
echo "$IP.$i is DOWN"
fi
#一个并发执行后要想管道中在加入一个空行，供下次使用
echo >&6
}&
done
wait
echo "END"