Ending a sentence with an abbreviation [duplicate]

I always stumble when using abbreviations in a sentence, as they inherently contain a period in them. How do I use a comma or a semicolon after an abbreviation? How about a period?

E.g. (This is an example of my quandary)

Solution 1:

Based on the "Oxford Manual of Style" I changed my approach:

• At the end of a sentence don't add a second period.
• For other punctuation still include the period. E.g. "IT.?" would be right.

But, when I was reading Mathematics at university I was told to always add the sentence ending period whatever went before, so if an equation ended with ellipsis there would be four periods together.

Summary: it is a matter of style.

Solution 2:

This pretty much explains who the period belongs to:

This one is simple enough: never double up periods. If a statement ends with “etc.” the period in the abbreviation does double duty, serving as the full stop to end the sentence. If, however, you need another mark of punctuation after an abbreviation, you can put it after the period

So, it really belongs to no one: it is shared. Your link would include the period.
N.B., emphasis added by me.

To ensure that there is only one period; taken from Wikipedia:

Abbreviations A full stop is used after some abbreviations.[3] If the abbreviation ends a declaratory sentence there is no additional full stop immediately following the full stop that ends the abbreviation (e.g., My name is Gabriel Gama, Jr.) This is called haplography. Logically there should be two full stops (one for the abbreviation, one for the sentence ending), but only one is conventionally written. In the case of an interrogative or exclamatory sentence ending with an abbreviation, a question or exclamation mark can still be added (e.g., Are you Gabriel Gama, Jr.?). [edit]