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Troff

From Academic Kids

Troff is a document processing system developed by AT&T for the Unix operating system.

Contents

History

Troff can trace its origins back to a text formatting program called RUNOFF, written by Jerome H. Saltzer for MIT's CTSS operating system in the mid-1960s. (The name allegedly 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 Roman 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 terminals. It understood everything troff did, and ignored the commands which were not applicable (e.g. font changes).

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 are thus currently three variants of the original Bell Labs troff:

  • An ancient variation from Bill Joy, still shipped by Sun.
  • The SoftQuad DWB, based on USL DWB 2.0 from 1994
  • The DWB 3.4 from Lucent Software Solutions (USL)

Use of troff and family was reduced somewhat in the 1990s, but it is still being used quite extensively. While Troff has been supplanted by other programs such as Interleaf, FrameMaker and LaTeX, it is still the default format of the UNIX documentation.

Features

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.

Extensive macro packages have been created for various document styles. A typical distribution of troff includes the me macros for formatting research papers, man macros for creating Unix man pages, and the ms macros for books, technical documentation, and reports.

As troff developed, 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 input, making 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.

Later, 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.

Reimplementations

groff is the GNU replacement for troff and nroff, and is free software.

References

Mel Melchner letter explaining roff/troff/DWB history and status (http://groups.google.com/groups?selm=DqA8Hy.Jyn%40research.att.com)

External links

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