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2 Features 3 Variants |
Troff can trace its origins back to a formatting program called runoff, written by J. E. Saltzer. It ran on MIT's CTSS operating system in the mid-sixties. The name came from the phrase at the time, I'll run off a document.
Bob Morris ported it to the GE 635 architecture and called the program roff (an abbreviation of runoff). It was rewritten as rf for the PDP-7, and at the same time (1969), Doug McIlroy rewrote an extended and simplified version of roff in the BCPL programming language.
The first version of Unix was developed on a PDP-7 which was sitting
around Bell Labs. In 1971 the developers wanted to get a PDP-11 for
further work on the operating system. In order to justify the cost for
this system, they proposed that they would implement a document
formatting system for the AT&T patents division. This first formatting
program was a reimplementation of McIllroy's roff, written by
Joe F. Ossanna.
When they needed a more flexible language, a new version of roff
called nroff (Newer 'roff') was written. It had a much more
complicated syntax, but provided the basis for all future versions.
When they got a Graphic Systems CAT Phototypesetter, Ossanna wrote a
version of nroff that would drive it. It was dubbed troff, for
typesetter 'roff', although many people have speculated that it
actually means Times 'roff' because of the use of the Times font
family in troff by default. As such, the name troff is pronounced
t-roff rather than trough.
With troff came nroff (they were actually almost the same program), which was for producing output for line printers and character terminalss. It understood everything troff
did, and ignored the commands which were not applicable (e.g. font
changes).
Since there are several things which cannot be done easily in
troff, work on several preprocessors began. These programs would
transform certain parts of a document into troff, which made a very
natural use of "pipes" in Unix -- sending the output of one program as the input to another (see pipes and filters).
The eqn preprocessor allowed mathematical formulae to be specified
in a much simpler and more intuitive manner. tbl is a preprocessor
for formatting tables. The refer preprocessor (and the similar
program, bib) processes citations in a document according to a
bibliographic database.
Unfortunately, Ossanna's troff was written in PDP-11
assembly language and produced output specifically for the CAT phototypesetter.
He rewrote it in C, although it was now 7000 lines of uncommented code
and still dependent on the CAT. As the CAT became less common, and was
no longer supported by the manufacturer, the need to make it support
other devices became a priority. However, before this could be done,
Ossanna was killed in an auto accident.
So, Brian Kernighan took on the task of rewriting troff. The
newly rewritten version produced a device independent code which was
very easy for postprocessors to read and translate to the appropriate
printer codes. Also, this new version of troff (called ditroff for
device independent 'troff') had several extensions, which included
drawing functions.
The troff collection of tools was eventually called Documenter's WorkBench (DWB), and was under continuous development in Bell Labs (renamed Unix System Laboratories, USL) through 1994. At that time, SoftQuad took over the maintenance, although Brian Kernighan continued to improve troff on his own. There is thus currently three variants of the original Bell Labs troff:
Troff features commands to designate fonts, spacing, paragraphs, margins, footnotes and more. Extensions are available for producing tables, diagrams, and mathematics. Inputs to troff are plain text files that can be created by any text editor.
As troff developed, several new preprocessors appeared. The pic preprocessor provides a wide range of drawing functions. Likewise the ideal preprocessor did the same, although via a much different paradigm. The grap preprocessor took specifications for graphs, but, unlike other
preprocessors, produced pic code.
Besides nroff, designed to generate formatted plain text instead of typeset output, groff is the GNU replacement for troff and nroff, and is free software.
History
Features
Variants
References