"Being in print" or "new" a is not well-defined in this context. "Being in print" is only a metaphor, since the process of printing is typically completed when a copy of a book is sold (and makes not sense in the case of publishing-on-demand, where it would be equivalent to "is available"); and "new" can mean "in its original condition" or "recently published" (with some uncertainty what time span "recently" denotes).

A more precise criterion would be whether a book is still on its publisher's backlist. As far as "The UNIX Programming Environment" is concerned, the answer is positive. Its publisher Prentice Hall was aquired by Simon & Schuster and later sold to Pearson.[1] On Pearson's Web-site the book is still available.[2]

[1] https://de.wikipedia.org/wiki/Prentice_Hall

[2] https://www.pearson.com/en-us/subject-catalog/p/unix-program...