1.shell编程-变量的高级用法

1.1.变量替换

变量替换的六种形式

实例：非贪婪和贪婪的区别

从头部删除

[root@VM_0_9_centos shell_learn]# var_1="i love you,do you love me"

[root@VM_0_9_centos shell_learn]# echo $var_1

i love you,do you love me

[root@VM_0_9_centos shell_learn]# var1=${var_1#*ov}

[root@VM_0_9_centos shell_learn]# echo $var1

e you,do you love me

[root@VM_0_9_centos shell_learn]# var2=${var_1##*ov}

[root@VM_0_9_centos shell_learn]# echo $var2

e me

[root@VM_0_9_centos shell_learn]#

从尾部删除

[root@VM_0_9_centos shell_learn]# var_1="i love you,do you love me"

[root@VM_0_9_centos shell_learn]# echo $var_1

i love you,do you love me

[root@VM_0_9_centos shell_learn]# var3=${var_1%ov*}

[root@VM_0_9_centos shell_learn]# echo $var3

i love you,do you l

[root@VM_0_9_centos shell_learn]# var4=${var_1%%ov*}

[root@VM_0_9_centos shell_learn]# echo $var4

i l

[root@VM_0_9_centos shell_learn]#

字符串替换，把bin替换成大写的BIN，单斜线和双斜线的区别

[root@VM_0_9_centos shell_learn]# echo $PATH

/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin

[root@VM_0_9_centos shell_learn]#

[root@VM_0_9_centos shell_learn]# var5=${PATH/bin/BIN}

[root@VM_0_9_centos shell_learn]# echo $var5

/usr/local/sBIN:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin

[root@VM_0_9_centos shell_learn]#

[root@VM_0_9_centos shell_learn]# var6=${PATH//bin//BIN}

[root@VM_0_9_centos shell_learn]# echo $var6

/usr/local/s/BIN:/usr/local//BIN:/usr/s/BIN:/usr//BIN:/root//BIN

[root@VM_0_9_centos shell_learn]#

1.2.字符串处理

计算字符串长度

方法一

${#string}

方法二

string有空格，则必须加双引号

expr length "$string"

实例

[root@VM_0_9_centos shell_learn]# var1="hello world"

[root@VM_0_9_centos shell_learn]# len=${#var1}

[root@VM_0_9_centos shell_learn]# echo $len

11

[root@VM_0_9_centos shell_learn]# len2=`expr length "$var1"`

[root@VM_0_9_centos shell_learn]# echo $len2

11

[root@VM_0_9_centos shell_learn]#

获取子串在字符串中的索引位置

expr index $string $substring

实例

[root@VM_0_9_centos shell_learn]# var1="quickstart is a app"

[root@VM_0_9_centos shell_learn]# index=`expr index "$var1" start`

[root@VM_0_9_centos shell_learn]# echo $index

6

[root@VM_0_9_centos shell_learn]# index2=`expr index "$var1" uniq`

[root@VM_0_9_centos shell_learn]# echo $index2

1

[root@VM_0_9_centos shell_learn]# index3=`expr index "$var1" cnk`

[root@VM_0_9_centos shell_learn]# echo $index3

4

[root@VM_0_9_centos shell_learn]#

会把子串分割成一个一个字符，index是最先找到的那个字符的位置。

计算子串长度

expr match $string substr

实例

[root@VM_0_9_centos shell_learn]# var1="quickstart is a app"

[root@VM_0_9_centos shell_learn]# len=`expr match "$var1" quic`

[root@VM_0_9_centos shell_learn]# echo $len

4

[root@VM_0_9_centos shell_learn]# len=`expr match "$var1" app`

[root@VM_0_9_centos shell_learn]# echo $len

0

[root@VM_0_9_centos shell_learn]# len=`expr match "$var1" quic.*`

[root@VM_0_9_centos shell_learn]# echo $len

19

[root@VM_0_9_centos shell_learn]#

必须从开头匹配才可以

抽取子串

实例

[root@VM_0_9_centos shell_learn]# var1="kafka hadoop yarn mapreduce"

[root@VM_0_9_centos shell_learn]# sub1=${var1:10}

[root@VM_0_9_centos shell_learn]# echo $sub1

op yarn mapreduce

[root@VM_0_9_centos shell_learn]# sub2=${var1:10:5}

[root@VM_0_9_centos shell_learn]# echo $sub2

op ya

[root@VM_0_9_centos shell_learn]# sub3=${var1: -5}

[root@VM_0_9_centos shell_learn]# echo $sub3

educe

[root@VM_0_9_centos shell_learn]# sub4=${var1:(-6)}

[root@VM_0_9_centos shell_learn]# echo $sub4

reduce

[root@VM_0_9_centos shell_learn]# sub5=${var1: -5:3}

[root@VM_0_9_centos shell_learn]# echo $sub5

edu

[root@VM_0_9_centos shell_learn]# sub6=`expr substr "$var1" 10 5`

[root@VM_0_9_centos shell_learn]# echo $sub6

oop y

[root@VM_0_9_centos shell_learn]#

注意：使用expr索引是从1开始计算，使用${string:position},索引从0开始计算。

1.3.字符串处理完整脚本

思路分析

1.将不同的功能模块划分，并编写函数

    function print_tips

    function len_of_string

    function del_hadoop

    function rep_hadoop_mapreduce_first

    function rep_hadoop_maapreduce_all

2.实现第一步所定义的功能函数

3.程序主流程的设计

vim example.sh

#!/bin/bash

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

function print_tips

{

    echo "******************************"

    echo "(1)打印string长度"

    echo "(2)删除字符串中所有的Hadoop"

    echo "(3)替换第一个Hadoop为Mapreduce"

    echo "(4)替换全部Hadoop为Mapreduce"

    echo "*******************************"

}

function len_of_string

{

    echo "${#string}"

}

function del_hadoop

{

    echo "${string//Hadoop/}"

}

function rep_hadoop_mapreduce_first

{

    echo "${string/Hadoop/Mapreduce}"

}

function rep_hadoop_mapreduce_all

{

        echo "${string//Hadoop/Mapreduce}"

}

while true

do

    echo "[string=$string]"

    echo

    print_tips

    read -p "Pls input your choice(1|2|3|4|q|Q): " choice

    case $choice in

        1)

            len_of_string

            ;;

        2)

            del_hadoop

            ;;

        3)

            rep_hadoop_mapreduce_first

            ;;

        4)

            rep_hadoop_mapreduce_all

            ;;

        q|Q)

            exit

            ;;

        *)

            echo "Error,input only in {1|2|3|4|q|Q|}"

            ;;

    esac

done

sh example.sh

1.4.命令替换

语法格式

方法一：

`command`

方法二：

$(command)

实例一：获取系统所有的用户并输出

cat /etc/passwd | cut -d ":" -f 1

vim example2.sh

#!/bin/bash

#

index=1

for user in `cat /etc/passwd | cut -d ":" -f 1`

do

    echo "This is $index user: $user"

    index=$(($index+1))

done

结果

实例二：根据当前当前时间计算今年和明年

$(())；两个括号主要用来进行整数运算

[root@VM_0_9_centos shell_learn]# date

Wed Jun 26 21:58:04 CST 2019

[root@VM_0_9_centos shell_learn]# date +%Y

2019

[root@VM_0_9_centos shell_learn]# echo "This is $(date +%Y) year"

This is 2019 year

[root@VM_0_9_centos shell_learn]# echo "This is $(($(date +%Y) + 1)) year"

This is 2020 year

[root@VM_0_9_centos shell_learn]#

实例三：根据当前时间获取今年还剩下多少星期和已经过了多少星期

[root@VM_0_9_centos shell_learn]# date +%j

177

[root@VM_0_9_centos shell_learn]# echo "This yaer have passed $(date +%j) days"

This yaer have passed 177 days

[root@VM_0_9_centos shell_learn]# echo "This yaer have passed $(($(date +%j)/7)) weeks"

This yaer have passed 25 weeks

[root@VM_0_9_centos shell_learn]# echo "今年还剩下$(((365 - $(date +%j))/7))星期"

今年还剩下26星期

[root@VM_0_9_centos shell_learn]#

实例四：判断nginx进程是否存在，若不存在则自动拉起该进程

[root@VM_0_9_centos shell_learn]# ps -ef |grep nginx

root      6658     1  0 22:33 ?        00:00:00 nginx: master process /usr/sbin/nginx

nginx     6659  6658  0 22:33 ?        00:00:00 nginx: worker process

root      6891   501  0 22:35 pts/0    00:00:00 grep --color=auto nginx

[root@VM_0_9_centos shell_learn]# ps -ef |grep nginx |grep -v grep |wc -l

2

[root@VM_0_9_centos shell_learn]# systemctl stop nginx

[root@VM_0_9_centos shell_learn]#

[root@VM_0_9_centos shell_learn]# ps -ef |grep nginx |grep -v grep |wc -l

0

[root@VM_0_9_centos shell_learn]# sh example3.sh

[root@VM_0_9_centos shell_learn]#

[root@VM_0_9_centos shell_learn]# ps -ef |grep nginx |grep -v grep |wc -l

2

[root@VM_0_9_centos shell_learn]#

vim example3.sh

如果nginx的进程个数为0，则拉起该进程

#!/bin.bash

#

nginx_process_num=$(ps -ef | grep nginx | grep -v grep | wc -l)

if [ $nginx_process_num -eq 0 ];then

    systemctl start nginx

fi

1.5.有类型变量

declare和typeset命令

declare和typeset命令两者等价
declare和typeset命令都是用来定义变量类型的

取消申明的变量

declare +r

declare +i

declare +a

declare +x

实例一：-r 将变量设为只读

[root@VM_0_9_centos shell_learn]# var1="hello world"

[root@VM_0_9_centos shell_learn]# var1="hello python"

[root@VM_0_9_centos shell_learn]# echo $var1

hello python

[root@VM_0_9_centos shell_learn]# declare -r var1

[root@VM_0_9_centos shell_learn]# var1="hello go"

-bash: var1: readonly variable

[root@VM_0_9_centos shell_learn]#

实例二：-i 将变量设为整数

shell中如果不声明，默认当做字符串处理

[root@VM_0_9_centos shell_learn]# num1=10

[root@VM_0_9_centos shell_learn]# num2=$num1+20

[root@VM_0_9_centos shell_learn]# echo $num2

10+20

[root@VM_0_9_centos shell_learn]# declare -i num2

[root@VM_0_9_centos shell_learn]# num2=$num1+20

[root@VM_0_9_centos shell_learn]# echo $num2

30

[root@VM_0_9_centos shell_learn]#

实例三：-a 将变量定义为数组

定义数组

[root@VM_0_9_centos shell_learn]# declare -a array

[root@VM_0_9_centos shell_learn]# array=("jones" "mike" "kobe" "jordan")

输出数组所有的内容

[root@VM_0_9_centos shell_learn]# echo ${array[@]}

jones mike kobe jordan

第一个元素

[root@VM_0_9_centos shell_learn]# echo ${array[0]}

jones

数组长度

[root@VM_0_9_centos shell_learn]# echo ${#array[@]}

4

删除元素

[root@VM_0_9_centos shell_learn]# unset array

1.6.Bash数学运算之expr

语法格式

需要加转义字符“\”

[root@VM_0_9_centos shell_learn]# num1=30

[root@VM_0_9_centos shell_learn]# num2=40

[root@VM_0_9_centos shell_learn]# expr $num1 \> $num2

0

[root@VM_0_9_centos shell_learn]# expr $num1 \< $num2

1

[root@VM_0_9_centos shell_learn]# expr $num1 + $num2

70

[root@VM_0_9_centos shell_learn]# expr $num1 - $num2

-10

[root@VM_0_9_centos shell_learn]# expr $num1 * $num2

expr: syntax error

[root@VM_0_9_centos shell_learn]# expr $num1 \* $num2

1200

1.7.Bash数学运算之bc

bc是bash内建的运算器，支持浮点数运算。内建变量scale可以设置，默认为0.

[root@VM_0_9_centos ~]# echo "23+35" | bc

58

[root@VM_0_9_centos ~]# echo "23.3+35" | bc

58.3

[root@VM_0_9_centos ~]# echo "scale=3;23.3/3.5" | bc

6.657

[root@VM_0_9_centos ~]#

巴特西