Sage vs Sag - giving commands
Hi,
Could you please help me understand the difference between "Sage" and Sag"
There is a saying that reads "Sage nicht alles, was du weißt, aber wisse immer, was du sagst."
I believe it roughly means "Don't say everything you know, but know everything you say"
But if I want to give the command "say nothing" it is "Sag nichts".

If both sentences are being directed to someone (du) why is one "sage" and the other "sag"?
I hope that makes sense!

Thank you very much :)

~Alex

Question

Sage vs Sag - giving commands
Hi, 
Could you please help me understand the difference between "Sage" and Sag" 
There is a saying that reads "Sage nicht alles, was du weißt, aber wisse immer, was du sagst."
I believe it roughly means "Don't say everything you know, but know everything you say"
But if I want to give the command "say nothing" it is "Sag nichts".

If both sentences are being directed to someone (du)  why is one "sage" and the other "sag"?
I hope that makes sense!

Thank you very much :)

~Alex

Answer

The form with the additional -e, such as "sage" is fading and considered somewhat old-fashioned. You can still find it in a lot of old sayings, but apart from these, we usually use the form without the -e ("sag!"). There is no difference in meaning between them.

Answer

There might be regional differences, but I use  the imperative form usually without e, such as 'sag'.
The word 'sage' as imperative exists in some proverbs. e.g. 'sage und schreibe' and your example. 
But in sentecnes such as: Sage mir doch endlich was du machen willst' you can use either.

Answer

By the way: Ich habe .. gewohnt. = I lived. = It is over. I don't live there anymore.  So: Ich wohne seit 2015 in Australien. A simplified rule: Use "Perfekt" in German in spoken language, when the action is over. Use  "Präteritum" in written language, when the action is over.

Answer

The Duden accepts both forms (https://www.duden.de/rechtschreibung/sagen)
So, there is no difference.
I use the form without the e, if possible. In that case: Sag mir die Wahrheit! And I taught it this way. But I would never correct someone who uses the other form.