Most non-compete agreements that I've seen and sometimes signed used a phrasing that prohibits "outside work that would be in competition with the employer's business offerings or interests." The better agreements explicitly spelled out an approval process for the employee to work on a potentially competing project after receiving approval from the employer. That allowed for open source contributions. The best agreements also had exclusion clauses for works the employee had started prior to employment, but those projects needed to be listed with the employer.
You will most definitely need to consult an attorney familiar with business practices in your locale. This has been a contentious area of law, and jurisdictions do vary in their interpretation.
The overall intent is to protect the employer's line of business. If the employer really is in the business of creating daily build scripts, then yes, the employee needs to acknowledge they can't do that outside of work without the employer's approval. If the daily build scripts are simply a means to an end and not necessarily a product offering, then the employee should be okay in crafting other build scripts.
A more practical scenario would be an employee who builds a hypervisor for company XYZ. Working on an open-source hypervisor would then be in conflict with XYZ's interests unless approval is given to work on the OSS project.
Non-competes can get problematic for employees of large companies. I used to work for a multinational firm with hundreds of thousands of employees and a few bazillion software and hardware product lines. It was hard finding projects that wouldn't necessarily compete with my employer's interests. OTOH, they were really good about approving OSS contributions that didn't compete with direct day-to-day duties.