6.2.1.1 Syntax

roff’s page description language is a sequence of tokens: single-letter commands or their arguments. Some commands accept a subcommand as a first argument, followed by one or more further arguments.

AT&T device-independent troff used whitespace minimally when producing output. GNU troff, in contrast, attempts to make its output more human-readable. The whitespace characters—tab, space, and newline—are always meaningful. They are never used to represent spacing in the document; that is done with horizontal (h, H) and vertical (v, V) positioning commands. Any sequence of space and/or tab characters is equivalent to a single space, separating commands from arguments and arguments from each other. Space is required only where omitting it would cause ambiguity. A line break separates commands. The comment character is a pound/hash sign (#), and marks the remainder of the line as a comment. A line comprising only whitespace after comment removal does nothing but separate input tokens.

The positioning commands noted above, and the command to write one glyph (c), each take a single argument; the former a signed integer, and the latter a printable ISO 646/“ASCII” character. A series of such commands could validly occur without spaces on an input line, but GNU troff follows each with a newline.

Some commands have a more complex syntax; the GNU troff extension command for writing glyph sequences (t) accepts a variable number of arguments. Those that draw geometric objects (D) or control the device (x) furthermore recognize subcommand arguments. Such commands thus must end with a newline. In GNU troff, the device extension (sub)command ‘x X’ uniquely supports a line continuation syntax; a single input line contains any other.