Shell Programming and Scripting

Hi,

I have a log file which amongst other text has these lines:

(id is always the same format - [A-Z][0-9][0-9][0-9])

e.g.

Code:

<username>user1</username>
<name>fdfsdf</name>
Multiple other tags
<id>A111</id>
<username>user2</username>
<name>fdfsdf</name>
Multiple other tags
<id>A222</id>
<username>user1</username>
<name>fdfsdf</name>
Multiple other tags
<id>A222</id>

etc

Is anyone able to say how i would:

a) do a count on the file for unique id's that have a username of 'user2'.
b) do a count on the file for all id's that have a username of 'user2'.
c) do a count on the file for all id's that do not have a username of 'user2'.

Thanks for any help that can be provided!!

Is this a homework assignment?