shell 字符串操作 + 变量替换

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本文详细介绍Shell脚本中字符串操作与变量替换的高级技巧，包括字符串长度获取、截取、替换及变量默认值设置等实用功能，适用于系统脚本编写。

本篇内容包括：

字符串操作
变量替换

1.字符串操作

表达式	含义
${#string}	获取字符串 string 的长度
${string:position}	从字符串 string position 处截取子串
${string:position:length}	从字符串 string position 处截取length 长度的子串
${string#substring}	从字符串 string 的开头，删除最短匹配 substring 的子串
${string##substring}	从字符串 string 的开头，删除最长匹配 substring 的子串
${string%substring}	从字符串 string 的结尾，删除最短匹配 substring 的子串
${string%%substring}	从字符串 string 的结尾，删除最长匹配 substring 的子串
${string/substring/replacement}	在字符串 string 中，使用 replacement 替换 substring
${string//substring/replacement}	在字符串 string 中，使用 replacement，代替所有匹配的 substring
${string/#substring/replacement}	条件替换：如果字符串 string 的前缀匹配 substring ，那么就用 replacement 来代替匹配到的 substring
${string/%substring/replacement}	条件替换：如果字符串 string 的后缀匹配 substring ，那么就用 replacement 来代替匹配到的 substring

1.获取长度：

zhang@zhang-virtual-machine:~/Desktop$ string='my blog nickName is xiao mu xi zi'
zhang@zhang-virtual-machine:~/Desktop$ echo $string
my blog nickName is xiao mu xi zi
zhang@zhang-virtual-machine:~/Desktop$ echo ${#string}
33
zhang@zhang-virtual-machine:~/Desktop$

2.字符串截取：

zhang@zhang-virtual-machine:~/Desktop$ echo $string
my blog nickName is xiao mu xi zi
zhang@zhang-virtual-machine:~/Desktop$ echo ${string:8}
nickName is xiao mu xi zi
zhang@zhang-virtual-machine:~/Desktop$ echo ${string:8:8}
nickName
zhang@zhang-virtual-machine:~/Desktop$

3.字符串替换：

zhang@zhang-virtual-machine:~/Desktop$ echo $string
my blog nickName is xiao mu xi zi
zhang@zhang-virtual-machine:~/Desktop$ echo ${string#my}
blog nickName is xiao mu xi zi
zhang@zhang-virtual-machine:~/Desktop$ echo ${string#my blog}
nickName is xiao mu xi zi
zhang@zhang-virtual-machine:~/Desktop$ echo ${string##my blog}
nickName is xiao mu xi zi
zhang@zhang-virtual-machine:~/Desktop$ echo ${string##zi}
my blog nickName is xiao mu xi zi
zhang@zhang-virtual-machine:~$ echo ${string%zi}
my blog nickName is xiao mu xi
zhang@zhang-virtual-machine:~$ echo ${string%%xi zi}
my blog nickName is xiao mu
zhang@zhang-virtual-machine:~$

zhang@zhang-virtual-machine:~/Desktop$ greet='hello,world,hello,linux'
zhang@zhang-virtual-machine:~/Desktop$ echo $greet
hello,world,hello,linux
zhang@zhang-virtual-machine:~/Desktop$ echo ${greet/hello/welcome to}
welcome to,world,hello,linux
zhang@zhang-virtual-machine:~/Desktop$ echo ${greet//hello/welcome to}
welcome to,world,welcome to,linux
zhang@zhang-virtual-machine:~/Desktop$ echo $greet
hello,world,hello,linux

zhang@zhang-virtual-machine:~/Desktop$ echo $greet
hello,world,hello,linux
zhang@zhang-virtual-machine:~/Desktop$ echo ${greet/#world/php}
hello,world,hello,linux
zhang@zhang-virtual-machine:~/Desktop$ echo ${greet/#hello/welcome to}
welcome to,world,hello,linux
zhang@zhang-virtual-machine:~/Desktop$ echo ${greet/%linux/php}
hello,world,hello,php
zhang@zhang-virtual-machine:~/Desktop$

2.变量替换

表达式	含义
${var-DEFAULT}	如果 var 没有被声明，那么就以 DEFAULT 作为其默认值
${var:-DEFAULT}	如果var没有被声明或者其值为空，那么就以 DEFAULT 作为其默认值
${var=DEFAULT}	如果var没有被声明，那么就以 DEFAULT 作为其默认值
${var:=DEFAULT}	如果var没有被声明或者其值为空，那么就以 DEFAULT 作为其默认值
${var+OTHERVALUE}	如果var声明了，那么其值就是 OTHERVALUE ，否则就为空字符串
${var:+OTHERVALUE}	如果var被设置了，那么其值就是 OTHERVALUE ，否则就为空字符串
${!varprefix*}	匹配之前所有以varprefix开头进行声明的变量
${!varprefix@}	匹配之前所有以varprefix开头进行声明的变量

zhang@zhang-virtual-machine:~/Desktop$ echo $name

zhang@zhang-virtual-machine:~/Desktop$ echo ${name-zhang}
zhang
zhang@zhang-virtual-machine:~/Desktop$ name=
zhang@zhang-virtual-machine:~/Desktop$ echo $name

zhang@zhang-virtual-machine:~/Desktop$ echo ${name:-zhang}
zhang
zhang@zhang-virtual-machine:~/Desktop$ echo ${name=zhang}

zhang@zhang-virtual-machine:~/Desktop$ echo ${name:=zhang}
zhang
zhang@zhang-virtual-machine:~/Desktop$

zhang@zhang-virtual-machine:~/Desktop$ echo $lastName

zhang@zhang-virtual-machine:~/Desktop$ echo ${lastName+guoping}

zhang@zhang-virtual-machine:~/Desktop$ lastName='xiao mu xi zi'
zhang@zhang-virtual-machine:~/Desktop$ echo ${lastName+guoping}
guoping
zhang@zhang-virtual-machine:~/Desktop$ echo ${lastName:+guoping}
guoping
zhang@zhang-virtual-machine:~/Desktop$

zhang@zhang-virtual-machine:~/Desktop$ varprefixName='zhang'
zhang@zhang-virtual-machine:~/Desktop$ varprefixLastName='guoping'
zhang@zhang-virtual-machine:~/Desktop$ fullName='guoping zhang'
zhang@zhang-virtual-machine:~/Desktop$ echo ${!varprefix*}
varprefixLastName varprefixName
zhang@zhang-virtual-machine:~/Desktop$ 
zhang@zhang-virtual-machine:~$ skillDynamicLanguage='php'
zhang@zhang-virtual-machine:~$ skillStaticLanguage='C++'
zhang@zhang-virtual-machine:~$ echo ${!Lanugage@}

zhang@zhang-virtual-machine:~$ echo ${!skill@}
skillDynamicLanguage skillStaticLanguage
zhang@zhang-virtual-machine:~$

以上所列，有点冷门(即用的比较少，有些系统脚本偶尔会用到)，不过掌握后还是能省去不少麻烦。