Linux man pages : groff_out (5)
groff_out - groff intermediate output format
This manual page describes the intermediate output format of the GNU
roff(7) text processing system. This output is produced by a run of
the GNU troff(1) program before it is fed into a device postprocessor
As the GNU roff processor groff(1) is a wrapper program around troff
that automatically calls a postprocessor, this output does not show up
normally. This is why it is called intermediate within the groff sys-
tem. The groff program provides the option -Z to inhibit postprocess-
ing, such that the produced intermediate output is sent to standard
output just like calling troff manually.
In this document, the term troff output describes what is output by the
GNU troff program, while intermediate output refers to the language
that is accepted by the parser that prepares this output for the post-
processors. This parser is smarter on whitespace and implements obso-
lete elements for compatibility, otherwise both formats are the same.
The pre-groff roff versions are denoted as classical troff.
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 com-
pletely different from the groff(7) language. While the groff language
is a high-level programming language for text processing, the interme-
diate 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 groff is fairly readable, while
classical troff output was hard to understand because of strange habits
that are still supported, but not used any longer by GNU troff.
During the run of troff, the roff input is cracked down to the informa-
tion on what has to be printed at what position on the intended device.
So the language of the intermediate output format can be quite small.
Its only elements are commands with or without arguments. In this doc-
ument, the term "command" always refers to the intermediate output lan-
guage, never to the roff language used for document formatting. There
are commands for positioning and text writing, for drawing, and for
Classical troff output had strange requirements on whitespace. The
groff output parser, however, is smart about whitespace by making it
maximally optional. The whitespace characters, i.e. the tab, space,
and newline characters, always have a syntactical meaning. They are
never printable because spacing within the output is always done by
Any sequence of space or tab characters is treated as a single syntac-
tical space. It separates commands and arguments, but is only required
when there would occur a clashing between the command code and the
arguments without the space. Most often, this happens when variable
length command names, arguments, argument lists, or command clusters
meet. Commands and arguments with a known, fixed length need not be
separated by syntactical space.
A line break is a syntactical element, too. Every command argument can
be followed by whitespace, a comment, or a newline character. Thus a
syntactical line break is defined to consist of optional syntactical
space that is optionally followed by a comment, and a newline charac-
The normal commands, those for positioning and text, consist of a sin-
gle letter taking a fixed number of arguments. For historical reasons,
the parser allows to stack such commands on the same line, but fortu-
nately, in groff intermediate output, every command with at least one
argument is followed by a line break, thus providing excellent read-
The other commands