What's GNU

This month's column discusses groff, the GNU version of troff.

As you are hopefully beginning to see, troff provides you all the mechanisms you need for complete control over your document's format. Unfortunately, this is often more control than you need. Writing documents using bare troff, while possible, can be quite painful. It is very much like programming in assembly language: you have complete control, and when the result works it works really well, but there is an awful lot of detail to keep track of, and it can be tedious and difficult.

To make it easier for regular users to manage the detail, troff allows you to define macros. A macro is like a subroutine in a programming language. You can group commands together to perform a larger task, and use the macro name, instead of writing out the entire sequence of commands each time.

Consider starting a new paragraph. You have to do the following tasks:

  • 1. See if there is room left on the page for at least two lines of text.

  • 2. Skip a space after the last paragraph.

  • 3. Indent the first line of text by 1/2 an inch.

You could write the commands to do this over and over again. But that is (a) tedious, (b) a hassle to update if you change how you do paragraphing. Instead, you can define a macro, say .P, to do this for you.

        .de P   \" DEfine paragraph macro
        .ne 3   \" we NEed at least three lines
        .sp     \" SPace down one line
        .ti .5i \" Temporary Indent .5 inches
        ..      \" end the macro definition

Then, in your text, you just put .P on a line by itself wherever you want a paragraph.

        .ds LX the Linux Operating System
        .ds LJ \fILinux Journal\fP
        If you are new to \*(LX, then you should subscribe to
        \*(LJ. It covers \*(LX in great detail,
        month after month.
        And even if you are an experienced user of \*(LX,
        \*(LJ will bring you valuable tips and tricks to keep
        your Linux system up and running.

One of the less attractive features of standard troff is that command, macro, string, and register names are limited to no more than two characters. Fortunately, groff allows longer names, with a different syntax for accessing them. In fact, groff has many nice extensions over troff, making the task of writing macro packages considerably easier. The extensions are documented in the gtroff(1) man page.

Popular Macro Packages

There are a number of popular troff macro packages. Using them is like programming in FORTRAN; it beats the heck out of Assembly Language, but it's not as nice as C or Modula-3.

The common macro packages are:

  • -ms - Manuscript macros. Originated in V7, popular on Berkeley Unix.

  • -man - Manual Page macros.

  • -mm - Memorandum Macros. Very powerful macros, popular on System V.

  • -me - Berkeley Technical Paper macros. An ugly package.

  • -mdoc - The new Document Macros from Berkeley.

  • -mandoc - A package that figures out dynamically if you want -man or -mdoc.

groff will support these directly if you have them, particularly using the -C compatibility mode option. It also has its own version of many of these packages.

The -ms and -mm are the most portable packages to use. -mm has many more features than -ms, thus making it harder to learn. In the long run though, the effort is worth it, because you can do so much.

Preprocessors For troff

Over the years, it was found that macros helped, but that there were some things that were just too difficult to do in bare troff, even with macro packages. The approach that was developed was to write a “little language” that solved a particular task, and to pre-process the language into raw troff. The common pre-processors are:

  • tbl - formats tables

  • eqn - formats equations

  • pic - formats pictures (diagrams)

  • grap - formats graphs

As an example, here is part of a table from a reference card I worked on:

        lfB l lfB l.
        abs~absolute value~int~integer part
        acos~arc cosine~log~natural logarithm
        asin~arc sine~sin~sine
        atan~arc tangent~sinh~hyperbolic sine
        cos~cosine~sqrt~square root
        cosh~hyperbolic cosine~tan~tangent

We'll explain it line by line. First, tbl only looks at lines between .TS (table start) and .TE (table end). Everything else is left alone. This makes it easy to use tbl in a pipeline with the other preprocessors. The first line sets the tab character to ~. Normally, tabs in the input separate each column of the table. For this table, a ~ is used to make it easier to mark off the columns.

Then, for each line of data in the table, you provide a line that describes the layout information. l means left justified, r means right justified, and c means centered. All the columns in this table are left justified. The first and third columns also use a different font (the f). Here, they are using the bold font.

In this example, there is only one control line, so it is applied to all the data lines. For more complicated tables, you have one control line per data line, with the last control line applying to any remaining data lines.

The other preprocessors are similar in functionality. grap is actually a preprocessor for pic.

Typically, the commands are used in a pipeline:

        grap doc.tr pic  tbl eqn  troff -mm -Tps > doc.ps

The actual usage will vary from machine to machine; we'll see below how to run groff.