Jon Greenbay pleaded guilty to the robbery charge as well as one count of theft under $1500 with previous convictions.
He's sentenced to six years in prison and will get 209 days credit for time already served in jail.
Last July, police were called to the Family Dollar on Brook St.
Officials say a clerk saw Greenbay taking items out of the store and confronted him in the parking lot.
Police say Greenbay pulled a knife on the clerk and told the clerk to go back inside before running off.
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