how long will an opened, store bought glass jar of tomato sauce last in a fridge?

Till it grows a beard.

At the first sight of something dark & fuzzy growing, either on the sauce or in the lid...pour it down the disposal.

If you haven't put anything into it, like a spoon, and it's kept properly chilled, it should be safe for several weeks because of the high acid content. I really wouldn't press my luck after that.

Always use a black marker pen (the sort with permanent ink) to date when any container of food stuff was placed in the refidge.

Takes the guess work out.

Remember: it's cheaper to throw out food you suspect has gone bad then a visit to the hospital for food poisoning.

Spaghetti sauce is one of the few things that holds it's flavor when frozen. I made a big batch of homemade spaghetti sauce, put it in small Tupperware containers and used on or two a month for a year. The last was as good as the first. But to answer your question, you'll use it before it goes bad.

tomato sauce - ages

tomato paste or pasta sauce - 3-5 days

it will last about a week. just remember when you chill tomatoes or tomato products they lose their flavor.

also if you use a little wine in you tomato sauce it amplifies the hell out of the flavor.

i have opened jars in the past and put them in my fridge and they last for at least two to three months

probably as long as salsa, a couple of months....you will know it is bad if you see mold, or bubbles. good luck.