Shell脚本使用sed命令时遇到变量的一些解决方案

关于SED命令我就不多说了，下面奉上我的例子

在写脚本配置YUM源的时候，总是以多多益善的想法为主，所以这时候就需要制定一个模版了，下面奉上我的Centos7源的模版

[base]
name=CentOS-$releasever - Base - URLS
failovermethod=priority
baseurl=URLS/centos/$releasever/os/$basearch/
        URLS/centos/$releasever/os/$basearch/
        URLS/centos/$releasever/os/$basearch/
gpgcheck=1
gpgkey=URLS/centos/RPM-GPG-KEY-CentOS-7
 
#released updates 
[updates]
name=CentOS-$releasever - Updates - URLS
failovermethod=priority
baseurl=URLS/centos/$releasever/updates/$basearch/
        URLS/centos/$releasever/updates/$basearch/
        URLS/centos/$releasever/updates/$basearch/
gpgcheck=1
gpgkey=URLS/centos/RPM-GPG-KEY-CentOS-7
 
#additional packages that may be useful
[extras]
name=CentOS-$releasever - Extras - URLS
failovermethod=priority
baseurl=URLS/centos/$releasever/extras/$basearch/
        URLS/centos/$releasever/extras/$basearch/
        URLS/centos/$releasever/extras/$basearch/
gpgcheck=1
gpgkey=URLS/centos/RPM-GPG-KEY-CentOS-7
 
#additional packages that extend functionality of existing packages
[centosplus]
name=CentOS-$releasever - Plus - URLS
failovermethod=priority
baseurl=URLS/centos/$releasever/centosplus/$basearch/
        URLS/centos/$releasever/centosplus/$basearch/
        URLS/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=URLS/centos/RPM-GPG-KEY-CentOS-7
 
#contrib - packages by Centos Users
[contrib]
name=CentOS-$releasever - Contrib - URLS
failovermethod=priority
baseurl=URLS/centos/$releasever/contrib/$basearch/
        URLS/centos/$releasever/contrib/$basearch/
        URLS/centos/$releasever/contrib/$basearch/
gpgcheck=1
enabled=0
gpgkey=URLS/centos/RPM-GPG-KEY-CentOS-7

在这个模版中，URLS属于我预设的镜像URL可替换变量名，所以我的思路就是只需要将这个变量名替换成一个可用的URL地址即可使用该源，但是这时候谁也不知道要将这个URLS替换成什么

所以这时候就需要使用变量来解决了，一开始的想法是将不确定的URL赋值到变量U里面，然后执行下面的指令

sed "s/URLS/$U/g" dome.repo

 然后提示错误了，于是我查了一下资料，得知这个SED指令可以自定义分隔符，因为  /  在shell中是有特殊的含义的，所以这时候只需要把这个符号换成其他的即可，比如#

 这时候就神奇的成功了,然后试一下&

 结果可见，涉及变量的时候只需要把斜杠换成其他符号即可