Meanings of doodly-squat in English

He's got a virus, and that stuff doesn't do doodly-squat for viruses.

I had never before grasped that doodly-squat was less than horsepucky, but it's always nice to learn something new.

"Not doodly-squat," I said.

"Then, you've got doodly-squat," she said and looked away, back to where Captain Matthews was answering questions with his solemn, manly jaw jutting out.