A short run is the time period in which one resource is fixed. Quantity of labor is variable but quantity of capital and production processes are fixed. Firms will produce if the market price at least covers variable costs, since fixed costs have already been paid and, as such, don't enter the decision-making process. The options a firm had to minimize losses are to reduce inventory levels, reduce variable costs, increase efficiency levels by linking it to production levels and reduce labor when the demand is low. A firm in perfect competition has no control over the market place. Sometimes that price may be so low that a firm loses money no matter how much it produces.
For a firm to shut down in the short run, the average variable cost can avoid paying by shutting down exceed the price it would get for selling the good. Such a firm can either continue to produce at a loss or temporarily shut down. In the situation that the price is lower than average total cost, it can minimize loss when it still produces, but if the price is lower than average variable cost, it can minimize loss