You can buy bottled pineapple syrup, but it’s easy to make excellent fresh syrup at home.
4 cups cane sugar
2 cups water
1 small pineapple
In a bowl or 2-quart jar, combine sugar with water and stir. Skin and cube a small pineapple and add the fruit to the sugar mixture. Let stand for 24 hours. Remove the pineapple cubes, lightly pressing them with a hand juicer or other method to squeeze some juice into the mixture. Stir to dissolve any residual sugar and pour the resulting syrup through a tea strainer or cheesecloth-lined funnel into a 1.5-liter bottle. Add a small dash of spirits (any distillate of at least 80-proof) as a preservative. Keep refrigerated for up to a month.