6.1 gtroff Output

This section describes the groff intermediate output format produced by GNU troff.

As groff is a wrapper program around GNU troff and automatically calls an output driver (or “postprocessor”), this output does not show up normally. This is why it is called intermediate. groff provides the option -Z to inhibit postprocessing such that the produced intermediate output is sent to standard output just as it is when calling GNU troff directly.

Here, the term troff output describes what is output by GNU troff, while intermediate output refers to the language that is accepted by the parser that prepares this output for the output drivers. This parser handles whitespace more flexibly than AT&T’s implementation and implements obsolete elements for compatibility; otherwise, both formats are the same.¹²⁴

The main purpose of the intermediate output concept is to facilitate the development of postprocessors by providing a common programming interface for all devices. It has a language of its own that is completely different from the gtroff language. While the gtroff language is a high-level programming language for text processing, the intermediate output language is a kind of low-level assembler language by specifying all positions on the page for writing and drawing.

The intermediate output produced by gtroff is fairly readable, while output from AT&T troff is rather hard to understand because of strange habits that are still supported, but not used any longer by gtroff.