1.shell編程-變數的高級用法_ZenDei技術網路在線

1.1.變數替換變數替換的六種形式實例：非貪婪和貪婪的區別從頭部刪除從尾部刪除字元串替換，把bin替換成大寫的BIN，單斜線和雙斜線的區別 1.2.字元串處理計算字元串長度方法一方法二 string有空格，則必須加雙引號實例獲取子串在字元串中的索引位置實例會把子串分割成一個一 ...

1.1.變數替換

變數替換的六種形式

實例：非貪婪和貪婪的區別

從頭部刪除

[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]#

從尾部刪除

[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]#

字元串替換，把bin替換成大寫的BIN，單斜線和雙斜線的區別

[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.字元串處理

計算字元串長度

方法一

${#string}

方法二

string有空格，則必須加雙引號

expr length "$string"

實例

[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]#

獲取子串在字元串中的索引位置

expr index $string $substring

實例

[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]#

會把子串分割成一個一個字元，index是最先找到的那個字元的位置。

計運算元串長度

expr match $string substr

實例

[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]#

必須從開頭匹配才可以

抽取子串

實例

[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]#

註意：使用expr索引是從1開始計算，使用${string:position},索引從0開始計算。

1.3.字元串處理完整腳本

思路分析

1.將不同的功能模塊劃分，並編寫函數
    function print_tips
    function len_of_string
    function del_hadoop
    function rep_hadoop_mapreduce_first
    function rep_hadoop_maapreduce_all

2.實現第一步所定義的功能函數

3.程式主流程的設計

vim example.sh

#!/bin/bash

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

function print_tips
{
    echo "******************************"
    echo "(1)列印string長度"
    echo "(2)刪除字元串中所有的Hadoop"
    echo "(3)替換第一個Hadoop為Mapreduce"
    echo "(4)替換全部Hadoop為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.命令替換

語法格式

方法一：
`command`

方法二：
$(command)

實例一：獲取系統所有的用戶並輸出

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

結果

實例二：根據當前當前時間計算今年和明年

$(())；兩個括弧主要用來進行整數運算

[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]#

實例三：根據當前時間獲取今年還剩下多少星期和已經過了多少星期

[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 "今年還剩下$(((365 - $(date +%j))/7))星期"
今年還剩下26星期
[root@VM_0_9_centos shell_learn]#

實例四：判斷nginx進程是否存在，若不存在則自動拉起該進程

[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的進程個數為0，則拉起該進程

#!/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.有類型變數

declare和typeset命令

declare和typeset命令兩者等價
declare和typeset命令都是用來定義變數類型的

取消申明的變數

declare +r
declare +i
declare +a
declare +x

實例一：-r 將變數設為只讀

[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]#

實例二：-i 將變數設為整數

shell中如果不聲明，預設當做字元串處理

[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]#

實例三：-a 將變數定義為數組

定義數組

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

輸出數組所有的內容

[root@VM_0_9_centos shell_learn]# echo ${array[@]}
jones mike kobe jordan

第一個元素

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

數組長度

[root@VM_0_9_centos shell_learn]# echo ${#array[@]}
4

刪除元素

[root@VM_0_9_centos shell_learn]# unset array

1.6.Bash數學運算之expr

語法格式

需要加轉義字元“\”

[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

實例：輸入一個正整數num，然後計算1+2+3+....+num的值，必須判斷num是否為正整數，不符合重新輸入

vim num.sh