Aaron James Campbell, 22, was released from custody on Tuesday morning after more than four months behind bars.

Acting Justice Richard Refshauge sentenced him in the ACT Supreme Court to two years and four months in jail, but suspended the rest of the term in favour of a drug and alcohol treatment order.

An agreed statement of facts shows Campbell entered the IGA supermarket in O'Connor not long after 8pm on August 4, when the owner was working there alone.

When Campbell left without paying for several items, including a $15 phone charger, the owner ran outside the shop to confront him.

Campbell struck the store owner in the face, prompting a bystander who saw this from his car to get out and try to apprehend the 22-year-old.

When Campbell saw this man coming, he pulled a 10cm fishing knife out of his bag and swung it at him.

The weapon narrowly missed the bystander's neck but made contact with his back.

While it did not pierce his skin, the blade cut a small hole in his jumper.

Campbell, homeless at the time, ended up dropping the knife and fleeing the area on foot.

He was arrested early on August 10, when, "showing signs of intoxicating substance abuse", he approached police officers in City Walk and told them he was wanted.

Campbell, who pleaded guilty in September to an aggravated robbery charge, was kept in custody from the date of his arrest until his sentencing on Tuesday morning.

Three months of his time behind bars was spent serving a sentence for two unrelated crimes, with the remaining 36 days referable to the robbery.

Campbell accepted a further jail sentence was necessary, but he sought that the balance of it be suspended and a drug and alcohol treatment order imposed.

He was assessed as both eligible and suitable for one of these, with Acting Justice Refshauge saying the 22-year-old had "expressed a desire to address his drug dependency".

The judge found Campbell, who has used various illicit drugs, was dependent on methamphetamine "and probably cannabis", with his addictions having substantially contributed to his offending.

The treatment order Acting Justice Refshauge ultimately imposed will run for two years, with Campbell required to spend at least the first half of it in a residential drug rehabilitation program.

MORE COURT AND CRIME NEWS:

Acting Justice Refshauge told Campbell, a man who routinely punched holes in walls during a "disturbed" and disadvantaged childhood, that his crime was "inexcusable".

The judge noted Campbell's use of violence during the robbery, observing that a knife was "always loaded" and capable of causing death.

He warned the 22-year-old drug dependency would be a lifelong struggle.

But he urged him to learn how to manage this "dreaded, pernicious" issue, and accept the help of professionals to prevent his problems getting "bigger than Ben-Hur".

Our journalists work hard to provide local, up-to-date news to the community. This is how you can continue to access our trusted content: