Justin Kevin Pearce, 25, of Bridgewater, pleaded guilty in April to causing grievous bodily harm by stabbing his brother twice from behind with a steak knife last year.

He was yesterday sentenced in the Supreme Court of Tasmania in Hobart to a 12-month, wholly suspended prison term by Justice Helen Wood.

Justice Wood said Pearce had an intellectual disability, had never worked and left school in grade 7.

She acknowledged he had a drinking problem, and said treatment was "imperative".

"The reason you've been given this chance is because I believe you can do it," she said.

His victim, Timothy Pearce, underwent surgery to remove the knife and suffered a punctured lung.

Pearce had consumed a carton of beer and a bottle of Jack Daniels whisky on the day of the attack and, when drinking with other friends, he was convinced to help "go and kill someone".

Pearce returned home to obtain a baseball bat and metal piping, and his brother and father attempted to stop him.

He produced a pocket knife, which was removed from him.

Pearce then grabbed a steak knife, and attacked his brother from behind.

His victim ran to get help from neighbours with the knife protruding from his back.

Pearce's nine-year-old nephew was present during the attack.

Justice Wood told Pearce the crime was a serious one, but took into account Pearce's "exceptional case".

She said he had a limited understanding of risk, but was very remorseful.

"This is a very serious crime, you could have even killed him," Justice Wood said.

"It is absolutely important that you stop drinking.

"You're going to have to work hard."

Pearce was ordered to attend a live-in rehabilitation program, not commit any further offences that would receive a prison term, and must attend counselling.