1、多线程执行

while read line
do
    echo $user
done < user.txt

2、while循环从文件中读取内容：适合处理文件

while read ip
do 
    {
        ping -c1 -W1 $ip &>/dev/null 
    }&
done < ip.txt
thread=5  #进程个数
tmp_fifofile=/tmp/$$.fifo  #创建管道
mkfifo $tmp_fifofile  
exec 8<> $tmp_fifofile  #打开文件描述符
rm $tmp_fifofile  
for i in `seq $thread`
do
    echo >&8           #往管道中加入5个空行，加入其他的内容也可以
done
while read ip
do 
    read -u 8       #每次读一行
    { 
         ping -c1 -W1 $ip &>/dev/null 
         echo >&8  #处理完后加入一行，使管道中一直有五行
    }&
done < ip.txt
wait
exec 8<&-  #关闭文件描述符

3、无限循环，:命令执行永久为true

while :
do
    #statements
done
while true
do
    #statements
done

4、判断：再次确认（输入y/n）

read -p "Are you sure? [y/n]" action
if [[ "$action" = "y" ]]; then
    #statements
fi
read -p "Are you sure? [y/n]" action
case $action in
    y|Y|YES|yes )
        ;;
esac

5、判断参数个数

if [[ $# -eq 0 ]]; then
    echo "参数个数为0"
    exit 1
fi

默认取所有参数$*
for i 
do
    #statements
done

6、提示用法

usage(){
        echo "Usage: `basename $0` (start|stop|restart|safeStart)"
        exit -1
}

7、$? ： 判断上一个命令执行是否成功

mkdir /usr/local/redis
if [[ $? -eq 0 ]]; then
    echo "ok"
fi

7、关联数组

declare -A hosts
while read line 
do 
    type=`echo $line |awk '{print $2}'`
    let hosts[$type]++
done </etc/hosts
for i in ${!hosts[@]}   #数组索引
do
    echo "$i: ${hosts[$i]}"
done

8、select选项

#!/usr/bin/bash
#$PS3赋值来修改提示符
PS3="command(5 for quit):"
select command in disk_partion fs cpu_load mem_util quit
do
    case $command in
        disk_partion )
            fdisk -l
            ;;
        fs )
            df -h
            ;;
        cpu_load )
            uptime
            ;;
        mem_util )
            free -m
            ;;
        quit)
            break
            ;;
        *)
            echo "erro"
            exit -1
    esac
done

可以使用循环自定义：

#!/bin/bash
help(){
    echo "Command action"
    echo "   a   toggle a bootable flag"
    echo "   b   edit bsd disklabel"
    echo "   c   toggle the dos compatibility flag"
    echo "   d   delete a partition"
    echo "   g   create a new empty GPT partition table"
    echo "   G   create an IRIX (SGI) partition table"
    echo "   l   list known partition types"
    echo "   m   print this menu"
    echo "   n   add a new partition"
    echo "   o   create a new empty DOS partition table"
    echo "   p   print the partition table"
    echo "   q   quit without saving changes"
    echo "   s   create a new empty Sun disklabel"
    echo "   t   change a partition's system id"
    echo "   u   change display/entry units"
    echo "   v   verify the partition table"
    echo "   w   write table to disk and exit"
    echo "   x   extra functionality (experts only)"
}
while [[ true ]]; do
    read -p "command(m for help):" command
    case $command in
        m )
            help
            ;;
        q )
            exit
            ;;
        * )
            help
            ;;
    esac
done