bash 字符串处理

时间:2021-09-23 10:37:11

bash 字符串处理

字符串切片:${var:offset:length}
示例:
[root@localhost ~]#mypath="/etc/sysconfig/network-scripts/"    #定义一个变量,等会切这个变量
[root@localhost ~]# echo ${mypath:5}       #偏移5个字符显示
sysconfig/network-scripts/
[root@localhost ~]# echo ${mypath:10}     #偏移10个字符显示
nfig/network-scripts/
[root@localhost ~]# echo ${mypath:5:5}    #偏移5个字符,取5个字符 
sysco

取出字符串的最后几个字符:${var: -length}
注意:-length之前有空白字符;
[root@localhost ~]# echo ${mypath: -10}
k-scripts/

基于模式取子串:
${var#*word}:自左而右,查找var变量中存储的字符串中第一次出现的由word所指明的字符,删除此字符及其左侧的所有内容;
示例:
[root@localhost ~]#mypath="/etc/sysconfig/network-scripts"
[root@localhost ~]# echo ${mypath#*/}
etc/sysconfig/network-scripts

${var##*word}:自左而右,查找var变量中存储的字符串中最后一次出现的由word所指明的字符,删除此字符及其左侧的所有内容;
[root@localhost ~]#mypath="/etc/sysconfig/network-scripts"
[root@localhost ~]# echo ${mypath##*/}
network-scripts

再举两个示例:
[root@localhost ~]#mypath="/etc/sysconfig/network-scripts"
[root@localhost ~]# echo ${mypath##*c}
ripts
[root@localhost ~]# echo ${mypath#*c}
/sysconfig/network-scripts

${var%word*}:自右而左,查找var变量中存储的字符串中第一次出现的由word所指明的字符,删除此字符及其右侧的所有内容;
${var%%word*}:自右而左,查找var变量中存储的字符串中最后一次出现的由word所指明的字符,删除此字符及其右侧的所有内容;

示例:
[root@localhost ~]#mypath="/etc/sysconfig/network-scripts"
[root@localhost ~]# echo ${mypath%c*}
/etc/sysconfig/network-s
[root@localhost ~]# echo ${mypath%%c*}
/et

示例:取一个URL的协议和端口
[root@localhost ~]#url="http://www.baidu.com:80"
[root@localhost ~]# echo ${url##*:}
80
[root@localhost ~]# echo ${url%%:*}
http

查找替换:   
${var/pattern/replacement}:查找var变量存储的字符中第一次由pattern匹配到的内容,并替换为replacement;
[root@localhost ~]#url="http://www.baidu.com:80"
[root@localhost ~]# echo ${url/www/WWW}
http://WWW.baidu.com:80
[root@localhost ~]# echo ${url/w/W}
http://Www.baidu.com:80

${var//pattern/replacement}:查找var变量存储的字符中所有能够由pattern匹配到的内容,并替换为replacement;
[root@localhost ~]# echo ${url//w/W}
http://WWW.baidu.com:80

${var/#pattern/replacement}:查找var变量存储的字符中最开始处能够由pattern匹配到的内容,并替换为replacement;
[root@localhost ~]# userinfo="root:x:0:0:rootuser:/root:/bin/bash"
[root@localhost ~]# echo ${userinfo/#root/ROOT}
ROOT:x:0:0:root user:/root:/bin/bash

${var/%pattern/replacement}:查找var变量存储的字符中最后位置能够由pattern匹配到的内容,并替换为replacement;
[root@localhost ~]# userinfo="root:x:0:0:rootuser:/root:/bin/root"
[root@localhost ~]# echo ${userinfo/%root/ROOT}
root:x:0:0:root user:/root:/bin/ROOT

查找删除:   
${var/pattern}:查找var变量存储的字符中第一次由pattern匹配到的内容,并删除;
${var//pattern}:查找var变量存储的字符中所有能够由pattern匹配到的内容,并删除;
${var/#pattern}:查找var变量存储的字符中最开始处能够由pattern匹配到的内容,并删除;
${var/%pattern}:查找var变量存储的字符中最后位置能够由pattern匹配到的内容,并删除;
示例:
[root@localhost ~]# userinfo="root:x:0:0:rootuser:/root:/bin/root"
[root@localhost ~]# echo ${userinfo/root}
:x:0:0:root user:/root:/bin/root
[root@localhost ~]# echo ${userinfo//root}
:x:0:0: user:/:/bin/
[root@localhost ~]# echo ${userinfo/#root}
:x:0:0:root user:/root:/bin/root
[root@localhost ~]# echo ${userinfo/%root}
root:x:0:0:root user:/root:/bin/

字符串大小写转换:
${var^^}:把var变量中的所有小写字母,统统替换为大写;
${var,,}:把var变量中的所有大写字母,统统替换为小写;
示例:
[root@localhost ~]# echo $userinfo
root:x:0:0:root user:/root:/bin/root
[root@localhost ~]# myinfo=${userinfo^^}
[root@localhost ~]# echo $myinfo
ROOT:X:0:0:ROOT USER:/ROOT:/BIN/ROOT
[root@localhost ~]# echo ${myinfo,,}
root:x:0:0:root user:/root:/bin/root

变量赋值:   
${var:-word}:如果变量var为空或未声明,则返回word所表示的字符串;否则,则返回var变量的值;
[root@localhost ~]# echo $name
                      #这行的值为空
[root@localhost ~]# echo ${name:-tom}
tom
[root@localhost ~]# name=hello 
[root@localhost ~]# echo ${name:-tom}
hello

${var:=word}:如果变量var为空或未声明,则返回word所表示的字符串,并且把word赋值为var变量;否则,则返回var变量的值;
[root@localhost ~]# echo $name
                     #这行的值为空
[root@localhost ~]# name=${name:-tom}
[root@localhost ~]# echo $name
tom
[root@localhost ~]# name=${name:-jerry}
[root@localhost ~]# echo $name
tom

${var:?error}:如果变量var为空或未声明,则返回error为错误信息;否则,则返回var变量的值;
[root@localhost ~]# echo "User's name is${name:?wrong}"
-bash: name: wrong
[root@localhost ~]# name=tom
[root@localhost ~]# echo "User's name is${name:?wrong}"
User's name is tom

${var:+word}:如果变量var为空或未声明,忽略;否则,则返回word;
[root@localhost ~]# unset name
[root@localhost ~]# echo "User's name is${name:+wrong}"
User's name is 
[root@localhost ~]# name=tom
[root@localhost ~]# echo "User's name is${name:+wrong}"
User's name is wrong

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