Learn Polish: Warto zbierać leśne grzyby, byle mieć atlas. - It is worth gathering forest mushrooms, provided you have a field guide.

The conjunction byle (provided that) is followed by an infinitive when the condition applies generally or shares a subject with the main clause, as seen here with the impersonal warto. If you were talking to a specific person, you would use a past tense form with a personal ending attached to the conjunction, such as byleś miał atlas (provided you had a field guide).

Could I use byleby instead of byle in this sentence?

Yes, byle and byleby are interchangeable here. Both set a minimal condition meaning provided that or as long as. The suffix -by just adds a slight bit of emphasis, but the grammatical rules and the overall meaning remain exactly the same.

Why do we use the imperfective zbierać instead of the perfective zebrać?

The sentence describes mushroom picking as a general, ongoing activity or hobby. Because it is not about completing a single, specific gathering event, the imperfective aspect is the natural choice after warto.

I thought an atlas was a book of maps. Is it really the word for a field guide?