I live in South Australia and we have similar laws.
It's legal to carry a knife for a lawful purpose.
It's illegal to carry a knife or any other object for use for self defense or for a weapon. Though in a typically dumb legal bit of logic, if you are caught carrying a weapon for defense, the charge is possession of an offensive weapon. Go figure.
Anyway in my jurisdiction (and as I understand it most if not all other Aussie juistictions) you can carry a knife for a lawful purpose (other than self defense, even though self defense is legal - again go figure).

So if they catch you with say a 5 inch fixed blade and you say "I use it to peel fruit" or at least "I plan to use it to peel fruit", Then they will probably not charge you.

If you have one of those itty bitty 1.5inch long swiss army knives and you say you carry it for self defense, you may wel be charged with possession of an offensive weapon.

So basically if you are asked what you use the knife for and you state a lawful purpose that is vaguely credible, and they have no evidence that you've actually done anything else with it, they will probably not try to charge you.
I.e. intent is basically what you say, unless they can show otherwise.

E.g. if they caught you with a knife while wearing a balaklava and hanging around an ATM at night, they might try to charge yu with POOW, whereas if they do a random search and you happen to have a scrapper 5 in your bag and say that you use it to open boxes at work, the they'll probably let you go.

Then we have certain other classes of knives which are simply illegal because their design is (apparently) inherently evil.E.g. double edged blades, bali songs, flick knives.

But this country is almost as bad as the UK for this sort of foolishness.
Some years ago a woman in (I think) a different state was prosecuted for carrying hair spray, as she told a policeman than she carried with the intent to spray it in an attackers face if she were attacked. I believe the prosecutions was successful.