shell sed 替换,该如何处理

shell sed 替换
# DocumentRoot /var/www
DocumentRoot /home/cxl/web
<Directory />
Options FollowSymLinks
AllowOverride None
</Directory>
# <Directory /var/www/>
<Directory /home/cxl/web/>
Options Indexes FollowSymLinks MultiViews
AllowOverride None
Order allow,deny
allow from all
</Directory>
ScriptAlias /cgi-bin/ /usr/lib/cgi-bin/
<Directory "/usr/lib/cgi-bin">
AllowOverride None
Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch
Order allow,deny
Allow from all
</Directory>

以上一段代码，想将“<Directory /var/www/>”后面内容的“AllowOverride None”替换为“AllowOverride All”，仅替换这一个，别的不变
用shell脚本怎么写？

------解决方案--------------------
sed '/<Directory \/var\/www\/>/,/AllowOverride None/s/AllowOverride None/AllowOverride All/' text