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 ~]#
标签：变量定义 image 变量的高级用法 cas 判断 hadoop bsp only frame
原文地址：https://www.cnblogs.com/gaidy/p/11757441.html
