Jamie Reginald Hall faced the Supreme Court in Hobart yesterday over the brazen daylight robbery of the Lenah Valley Newsagency last August.

The court heard Hall, then 38, ran into the shop about 4.30pm.

He was wearing a home- made balaclava and armed with a 30-centimetre kitchen knife.

Prosecutors said the offender jumped over the counter, lunging at a 15-year-old employee while wielding the knife "menacingly" above his head.

The court heard when shop owner John Carney stood between Hall and the girl, the offender thrust the knife twice at Mr Carney's chest, slicing through two layers of clothing.

Crown prosecutor Allison Shand said Hall threatened the shop owner, screaming: "You're f--- dead, you're f--- dead, I'm going to kill you, where's the money?"

CCTV footage played in court showed Hall emptying several tills of more than $2200, before fleeing on foot.

The court heard Mr Carney pursued Hall into the street but lost sight of him.

Ms Shand said the offender hid under a nearby house, where his clothing, balaclava and knife were later recovered.

Hall was caught by police about an hour later, with most of the stolen money secreted in his sock.

Ms Shand said the violence Hall used was extreme.

"It was good luck, rather than good measure, that Mr Carney was not injured or killed," Ms Shand said.

The defence said drug use had a "prolific impact" on Hall's life choices, and his decision to commit the armed robbery was spontaneous.

The defence said Hall had shown remorse by pleading guilty, and said a crushing sentence should not be imposed.

Hall committed the crime while on bail for charges connected with the armed robbery of a Moonah hotel early last year.

He will be sentenced for both offences on April 30.