1.shell编程之变量的高级用法

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 ~]#