View source for Grepping in XML and other structured files

Sometimes you need to grep in a HTML file or an XML file or other kinds of files which are not line-based.  This is usually hard or painful using your standard grepping tools.  Luckily there's a wonderful tool called '''sgrep''' which does exactly this sort of thing.  You'll find it in apt if you're using Ubuntu and probably ports if you are using a BSD and if not, you're being really difficult but its homepage might be [http://www.cs.helsinki.fi/u/jjaakkol/sgrep.html].

Here's an example to show how you might yank all the virtualhost directives out of a httpd.conf:
 grep -v ^# httpd.conf | sgrep -i '"<virtualhost".."</virtualhost>"'
(Note how you must use regular grep to remove comments first, because they ''are'' line-based.)

Yay!

Also in apt I found a tool called '''xgrep''' (homepage probably [http://wohlberg.net/public/software/xml/xgrep/]) which is less neat than sgrep but might work better for some cases when you have well-formed XML files (which httpd.conf certainly isn't), because it allows you to specify tag ancestry and such.

And a small tip for dealing with ugly XML files: Expat comes with a tool called '''xmllint''' which is able to reformat files thus:
 xmllint --format - <uglymess.xml

That'll be $5.