$ cat header 
<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">

$ cat footer 
</urlset>

$ cat header file footer
<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
one line
</urlset>

在bash循环中包装上述内容：

To wrap the above in a bash-loop:

for f in *.xml; do cat header $f footer > tmp && mv tmp $f; done