Shell Script Programming Advanced

Shell Script Programming Advanced

Process Control

过程式编程语言    顺序执行    选着执行    循环执行

Conditional Select if statement

选择执行注意：if语句可嵌套单分支    if判断条;then        条件为真的分支代码    fi双分支：    if判断条件；then        条件为真的分支的代码     else        条件为假的分支代码    

If statement

    多分支     if 判断条件1; then          条件1为真的分支代码    elif 判断条件2; then         条件2为真的分支代码     elif 判断条件3; then         条件3为真的分支代码    else        以上条件都为假的分支代码    fi逐条件进行判断，第一次遇为“真”条件时，执行其分支，而后结束整个if语句  

If example

    根据命令的退出状态来执行命令if ping -c1 -W2 station1 &> /dev/null; then    echo ‘Station1 is UP‘elif grep "station1" ~/maintenance.txt &> /dev/null; then    echo ‘Station1 is undergoing maintenance‘else    echo ‘Station1 is unexpectedly DOWN!‘    exit 1fi  

Conditional Judgment: Case statement

Cycle

    循环执行    将某代码段重复运行多次    重复运行多少次        循环次数事先已知        循环次数事先未知    有进入条件和退出条件for, while, until  

For loop

    The for variable name in list; Do loop body done for i[i represents the variable name] in {1..10}; "In followed by the list" do Userdel-r user$i; The "Do and do" is the loop body execution mechanism: The elements in the list are assigned to the "variable name" in turn; The loop body is executed once each assignment; Until the element in the list is exhausted, the loop end example: [[email protected]:11:44bin] #sum = 0; For NUM in 1 4 6 4;do Sum=$[sum+num]; Done echo sum= $sum sum=38 [[[Email protected]:12:58bin] #for num in 1 4 6 4;do echo "num= $num";d one num=1 num =23 num=4 num=6 num=4 [[email protected]:13:24bin] #sum = 0; For num in {1..100};d o sum=$[sum+num]; Done echo sum= $sum sum=5050 [[email protected]:16:24bin] #sum = 0; For num in ' seq ';d o sum=$[sum+num]; Done echo sum= $sum sum=55 [[email protected]:16:47bin] #sum = 0; For num in {1..100..2};d o sum=$[sum+num]; Done echo sum= $sum sum=2500 Example: Calculates 1 to 100 and [[email protected]:27:29bin] #sum = 0; For i in {1..100};d o sum=$[sum+i];d one;echo sum= $sum sum=5050 [[email protected]:27:44bin] #sum = 0; For i in ' SEQ 1 2 ';d o sum=$[sum+i];d one;echo sum= $sum   sum=2500 

For loop

列表生成方式：(1) 直接给出列表(2) 整数列表：    (a) {start..end}    (b) $(seq [start [step]] end)(3) 返回列表的命令    $(COMMAND)(4) 使用glob，如：*.sh(5) 变量引用；   [email protected], $*  

While loop

    while CONDITION; do        

Until cycle

    until CONDITION; do        循环体done进入条件： CONDITION 为false退出条件： CONDITION 为true  

Loop Control statement Continue

Loop control Statement Break

    用于循环体中break [N]：提前结束第N层循环，最内层为第1层 while CONDTIITON1; doCMD1...if CONDITION2; thenbreakfiCMDn... done  

Loop Control Shift Command

    shift [n]用于将参量列表 list 左移指定次数，缺省为左移一次。参量列表 list 一旦被移动，最左端的那个参数就从列表中删除。while 循环遍历位置参量列表时，常用到 shift./doit.sh a b c d e f g h./shfit.sh a b c d e f g h

Example: doit.sh

    #!/bin/bash# Name: doit.sh# Purpose: shift through command line arguments# Usage: doit.sh [args]while [ $# -gt 0 ] # or (( $# > 0 ))do echo $* shiftdone示例：shift.sh#!/bin/bash#step through all the positional parametersuntil [ -z "$1" ]do echo "$1" shiftdoneecho  

Create an infinite loop

while true; do循环体doneuntil false; do循环体Done

Shell Script Programming Advanced