Ini duplicate find

I have a ini file with different sections, like this:

[section1]
c:\=1
d:\=1
e:\=1
d:\=1

[section2]
c:\=1

Is there a way to find duplicates within the same section and between sections?

For example. My gui adds keys to these sections in to different places. One to allow (section1) and another to block (section2). When i try to add something to section1 (for ex.), i want my script to search for duplicates in section1 and in section2 and warn me if any duplicates were found.

Basic question is...: How can i search ini files for duplicates (without using arrays)?