shell 流程结构

if 判断语句

            if [ $a == $b ]
            then
                echo "等于"
            else
                echo "不等于"
            fi

case分支选择

            case $xs in
            ) echo "" ;;
            ) echo "" ;;
            *) echo "其他" ;;
            esac

while循环

            # while true  等同   while :
            # 读文件为整行读入
            num=
            while [ $num -lt  ]
            do
            echo $num
            ((num=$num+))
            done
            ###########################
            grep a  a.txt | while read a
            do
                echo $a
            done
            ###########################
            while read a
            do
                echo $a
            done < a.txt 

for 循环

            # 读文件已空格分隔
            w=`awk -F ":" '{print $1}' c`
            for d in $w
            do
                $d
            done
            ###########################
            for ((i=;i<${#o[*]};i++))
            do
            echo ${o[$i]}
            done

until 循环

            #  当command不为0时循环
            until command
            do
                body
            done

流程控制 

            break N     #  跳出几层循环
            continue N  #  跳出几层循环，循环次数不变
            continue    #  重新循环次数不变