Shell编程学习笔记(二)-变量的高级用法

1.变量替换

 

example1:根据匹配规则删除变量部分内容 

example2:根据匹配规则替换变量部分内容

 

2.字符串处理

注意： ${}计算索引是从0开始 expr计算索引是从1开始。

 

3.关于字符串的完整脚本实例

#!/bin/bash

string="Bigdata process framework is Hadoop,Hadoop is an open source project"

function tips_info
{
        echo "*********************************"
        echo "*** (1) 打印string长度"
        echo "*** (2) 在整个字符串中删除Hadoop"
        echo "*** (3) 替换第一个Hadoop为Mapreduce"
        echo "*** (4) 替换全部Hadoop为Mapreduce"
        echo "*********************************"
}

function print_len
{
        if [ -z "$string" ];then
                echo "Error,string is null"
                exit 1
        else
                echo "${#string}"
        fi
}
function del_hadoop
{
        if [ -z "$string" ];then
                echo "Error,string is null"
                exit 1
        else
                echo "${string//hadoop/}"
        fi
}

function rep_hadoop_mapreduce_first
{
        if [ -z "$string" ];then
                echo "Error,string is null"
                exit 1
        else
                echo "${string/Hadoop/Mapreduce}"
        fi
}
function rep_hadoop_mapreduce_all
{
        if [ -z "$string" ];then
                echo "Error,string is null"
                exit 1
        else
                echo "${string//Hadoop/Mapreduce}"
        fi
}

while true
do

echo "[string=\"$string\"]"
tips_info
read -p "please Switch a Choice: " choice

case "$choice" in
        1)
                echo
                echo "Length Of String is:`print_len`"
                echo
                continue
                ;;
        2)
                echo
                echo "删除Hadoop后的字符串为:`del_hadoop`"
                ;;
        3)
                echo
                echo "替换第一个Hadoop后的字符串为:`rep_hadoop_mapreduce_first`"                                        
                ;;
        4)
                echo
                echo "替换全部的Hadoop后的字符串为:`rep_hadoop_mapreduce_all`"
                ;;

        q|Q)
                exit 0
                ;;
        *)
                echo "error,unlegal input,legal input only in { 1|2|3|4|q|Q }"
                continue
                ;;
esac
done

4.命令替换

命令替换：将某一个变量的输出结果作为另一变量的一部分

语法格式：

1. `command`

2.$(command) 

例1-获取配置文件中的配置名

配置文件如下所示

[hadoop]
username=12231
hadoop_client=12231
hadoop_output=12231
python_interpreter=pypy
queue_name=12231
hadoop_client_tianqi=12231
hadoop_output_tianqi=12231
queue_name_tianqi=12231

sql_client=/home/work/songhzwg/mysql/mysql-5.1.49/client/mysql

[email]
send_mail=true

#!/bin/bash
#打印配置文件的配置名

index=1

for conf_name in `cat ~/Desktop/config.conf | cut -d "=" -f 1`
do
	echo "This is $index config name: $conf_name"
	index=$((index + 1))
done

输出如下结果:

This is 1 config name: [hadoop]
This is 2 config name: username
This is 3 config name: hadoop_client
This is 4 config name: hadoop_output
This is 5 config name: python_interpreter
This is 6 config name: queue_name
This is 7 config name: hadoop_client_tianqi
This is 8 config name: hadoop_output_tianqi
This is 9 config name: queue_name_tianqi
This is 10 config name: sql_client
This is 11 config name: [email]
This is 12 config name: send_mail

知识点：1.命令替换 2.cut(-d 指定分割名 -f指定分割后的结果列表索引)

例2-根据系统时间计算今年或明年

 echo "Next year is $((`date +%Y` + 1))"

5.有类型变量

declare 声明变量类型

declare -r 声明变量为只读类型 eg:declare -r var="hello"

declare -i 声明变量为整形

declare -f 显示系统自定义的函数和内容

declare -F 显示定义的函数

 

declare -a array 声明一个数组

array=("jones" "mike" "kobe" "jordan")

1.输出数组内容：

echo ${array[@]} 输出全部内容

echo ${array[1]} 输出下标索引为1的内容

2.获取数组长度

echo ${#array}

3.赋值

array[0]="lily"

array[20]="hanmeimei"

4.删除元素

unset array[2]

unset array 清空整个数组

5.切片访问

${array[@]:1:4} 索引1到3的元素

6.数组遍历

for v in ${array[@]}

do

          echo $v

done