How can we control the length of output?

When we generate the results like the following:

export DATA_DIR=../data
python run_eval.py sshleifer/distilbart-cnn-12-6 $DATA_DIR/test.source ../output/result.txt \
    --reference_path $DATA_DIR/test.target \
    --score_path ../output/score.json \
    --task summarization \
    --device cuda \
    --fp16 \
    --bs 32

How can we control the length of the output? Like we want to have less than 100 tokens in the output.

Thank you!