shell脚本编程总结

原创
2016/10/26 19:06
阅读数 83

shell脚本:

         是一门解释行语言

        分类:

              ksh
               tcsh
                sh
                bash

查看系统支持的shell
            /etc/shells
查看当前使用shell
            echo $SHELL                

shell数据类型:
        字符型:
            'sads' '1233' "jhsdajks"
        数值型:
            123 1 2 3 5

 shell变量:
        变量:一段被命名的内存空间
        变量名:
            一般具有实际意义的单词缩写
            不能以关键字或特殊字符作为变量
            不能以数字开头作为变量
        定义变量:
            variable_name=value
            aa='123'
            bb=123
        变量分类:
            环境变量:全系统都能使用的变量
                     printenv,env
                     定义环境变量export variable_name=value
                     在shell当中直接定义只在当前shell终端窗口生效
                     永久生效:/etc/profile
                     某用户生效:~/.bashrc

            局部变量:

 定义:aa=123
                    在shell当中直接定义只在当前shell终端窗口生效
                    或者只在脚本内生效

            特殊变量:
                    $?:表示上一条执行指令的返回状态码
                    $n:n表示整数,$1表示脚本后面所跟的第一个参数
                    $0:表示脚本名称
                    $#:所有参数的个数
                    $*:列出所有的参数
                    $@:列出所有的参数
                    $$:查看脚本执行时的进程号


        运算符:
            数值运算符:
                    +:加
                    -:减
                    *:乘
                    /:商取整  10/3 3
                    %:取余    10%3 1
                    **:取幂   10**3 1000

            布尔值预算符:
                    &&:与运算
                    ||:或运算
                    !:非运算

            关系运算符:
                    $aa和$$bb是数值
                    >:大于 [ $aa -gt $bb ]
                    <:小于 [ $aa -lt $bb ]
                    <=:小于等于 [ $aa -le $bb ]
                    >=:大于等于 [ $aa -ge $bb ]
                    ==:等于     [ $aa -eq $bb ]
                    !=:不等于   [ $aa -ne $bb ]
        shell语法:
            第一行必须以#!/bin/bash作用指定解释器 必要
            最好有缩进习惯 非必要
            要有注释信息   非必要

            打印:
                #!/bin/bash
                #
                #
                echo "hello world"
                echo 'hello world'
                "":弱引用 echo "$aa" 引用的是aa变量的值
                '':强引用 echo '$aa' 就是打印$aa
                echo -e '\t'打印一个制表符

                printf "username:%s uid:%d" $user $uid
                格式化输出
                        %s字符变量占位符
                        %d整数变量占位符
                        %f浮点变量占位符
                        %cASCII变量占位符

            命令替换:
                    `command`:tab键上面的那个符号,专业一点叫做反引号
                     a=`date`:表示把变量名a的作用变为date指令

            循环:
                for 变量 in 范围
                    do
                        代码块
                    done

                for i in {1..10}
                    do
                        echo $i
                    done
                for i in `cat /etc/passed`
                    do
                        echo $i
                    done
                for i in 1 2 3 4 5
                    do
                        echo $i
                    done
                for i in ${array_name[*]}
                    do
                        echo $i
                    done
                注意循环可以嵌套
                    for i in {1..9}
                        do
                            for j in {1..9}
                                do
                                    $((i*j))
                                done
                        done
            while循环:
                    while 条件
                        do
                            代码块
                        done
                    当条件为真的时候执行代码块
                    i=0
                    while [ $i -le 10 ]
                        do
                            echo $i
                            let i++
                        done
                    死循环:
                        while true
                            do
                                代码块
                            done

            跳出循环:
                    break:跳出当前循环体
                    continue:跳出本次循环
                    exit:推出循环程序
                    
            条件判断:
                    if 条件;then
                        代码块1
                    else
                        代码块2
                    fi
                    条件为真的时候执行代码块1,其他情况执行代码块2
                    if 1>2;then
                        echo 'ok'
                    else
                        echo 'bad'
                    fi
                    
                    if [ $a ];then
                        echo 'ok'
                    else
                        echo 'bad'
                    fi
                    表明$a存在时执行ok不存在执行bad

                    条件判断的嵌套
                            if 条件1;then
                                代码块
                            elif 条件2;then
                                代码块2
                            else
                                代码块3
                            fi
                            如果满足条件1执行代码块1
                            满足条件2执行代码块2
                            其他情况执行代码块3

        分支选择:
                case 变量 in
                    条件1)
                        代码块1
                        ;;
                    条件2)
                        代码块2
                        ;;
                        *)
                        代码块3
                        ;;
                esac

                read -e -p 'please:' a
                case $a in
                    1)
                    echo '$a'
                    ;;
                    [a-z])
                    echo $a
                    ;;
                    quit|exit)
                    exit 4
                    ;;
                    *)
                    echo '其他非匹配输入'
                    ;;
                    注意:脚本是按照顺询执行的所以需要把*写在最后,以免其他的模式被屏蔽

 

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