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# 5. Programming Tutorial

This chapter covers all of the facilities of gtroff. Users of macro packages may skip it if not interested in details.

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## 5.1 Text

gtroff input files contain text with control commands interspersed throughout. But, even without control codes, gtroff will still do several things with the input text: filling and adjusting, adding additional space after sentences, hyphenating and inserting implicit line breaks.

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### 5.1.1 Filling and Adjusting

When gtroff reads in text it collects words from input and fits as many of them together on one output line as it can. This is known as filling.

Once gtroff has a filled line it will try to adjust it. This means it will widen the spacing between words until the text reaches the right margin (in the default adjustment mode). Extra spaces between words are preserved, but spaces at the end of lines are ignored. Spaces at the front of a line will cause a break (breaks will be explained in 5.1.5 Implicit Line Breaks)

See section 5.8 Manipulating Filling and Adjusting.

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### 5.1.2 Hyphenation

Since the odds are not great for finding a set of words, for every output line, which will fit nicely on a line without inserting excessive amounts of space between words, gtroff will hyphenate words so that lines can be justified without there being too much space between words. It uses an internal hyphenation algorithm (a simplified version of the algorithm used within TeX) to indicate which words can be hyphenated and how to do so. When a word is hyphenated the first part of the word will be added to the current filled line being output (with an attached hyphen), and the other portion will be added to the next line to be filled.

See section 5.9 Manipulating Hyphenation.

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### 5.1.3 Sentences

Although it is often debated, some typesetting rules say there should be different amounts of space after various punctuation marks. For example, the Chicago typsetting manual says that a period at the end of a sentence should have twice as much space following it as would a comma or a period as part of an abbreviation.

gtroff does this by flagging certain characters (normally !', ?' and .') as end of sentence characters. When gtroff encounters one of these characters at the end of a line it will append two sentence spaces in the formatted output. (This justifies one of the conventions mentioned in 5.2 Input Conventions.)

In addition, the following characters resp. glyphs are treated transparently while handling end of sentence characters: "', '', )', ]', *', dg, and rq.

See the cflags request in 5.17.4 Using Symbols, for more details.

To prevent the insertion of extra space after an end of sentence character (at the end of a line), append \&.

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### 5.1.4 Tab Stops

gtroff translates tabulator characters, also called tabs (normally code point ASCII 0x09 resp. EBCDIC 0x05), in the input into movements to the next tabulator stop. These tab stops are initially located every half inch across the page. Using this, simple tables can easily be made. However, it can often be deceptive as the appearance (and width) of the text on a terminal and the results from gtroff can vary greatly.

Also, a possible sticking point is that lines beginning with tab characters will still be filled, again producing unexpected results. For example, the following input

 1 2 3 4 5

will produce

 1 2 3 4 5

See section 5.11 Tabs and Fields.

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### 5.1.5 Implicit Line Breaks

An important concept in gtroff is the break. When a break occurs, gtroff will output the partially filled line (unjustified), and resume collecting and filling text on the next output line.

There are several ways to cause a break in gtroff. A blank line will not only cause a break, but it will also cause a one line vertical space (effectively a blank line) to be output.

A line which begins with a space will cause a break and the space will be output at the beginning of the next line. Note that this space isn't adjusted, even in fill mode.

The end of file will also cause a break -- otherwise the last line of the document may vanish!

Certain requests also cause breaks, implicitly or explicitly. This will be discussed in 5.8 Manipulating Filling and Adjusting.

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## 5.2 Input Conventions

Since gtroff does filling automatically, it is traditional in groff not to try and type things in as nicely formatted paragraphs. These are some conventions commonly used when typing gtroff text:

• Break lines after punctuation, particularly at the end of a sentence, and in other logical places. Keep separate phrases on lines by themselves, as entire phrases are often added or deleted when editing.

• Try to keep lines less than 40-60 characters, to allow space for inserting more text.

• Do not try to do any formatting in a WYSIWYG manner (i.e., don't try and use spaces to get proper indentation).

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## 5.3 Measurements

gtroff (like any other programs) requires numeric parameters to specify various measurements. Most numeric parameters(4) may have a measurement unit attached. These units are specified as a single character which immediately follows the number or expression. Each of these units are understood, by gtroff, to be a multiple of its basic unit. So, whenever a different measurement unit is specified gtroff converts this into its basic units. This basic unit, represented by a u', is a device dependent measurement which is quite small, ranging from 1/75th to 1/72000th of an inch. The values may be given as fractional numbers; however, fractional basic units are always rounded to integers.

Some of the measurement units are completely independent of any of the current settings (e.g. type size) of gtroff.

i
Inches. An antiquated measurement unit still in use in certain backwards countries. One inch is equal to 2.54cm.

c
Centimeters. One centimeter is equal to 0.3937in.

p
Points. This is a typesetter's measurement used for measure type size. It is 72 points to an inch.

P
Pica. Another typesetting measurement. 6 Picas to an inch (and 12 points to a pica).

s
z
See section 5.18.2 Fractional Type Sizes, for a discussion of these units.

The other measurements understood by gtroff are dependent on settings currently in effect in gtroff. These are very useful for specifying measurements which should look proper with any size of text.

m
Ems. This unit is equal to the current font size in points. So called because it is approximately the width of the letter m' in the current font.

n
Ens. This is half of an em.

v
Vertical space. This is equivalent to the current line spacing. See section 5.18 Sizes, for more information about this.

M
100ths of an em.

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### 5.3.1 Default Units

Many requests take a default unit. While this can be helpful at times, it can cause strange errors in some expressions. For example, the line length request expects em units. Here are several attempts to get a line length of 3.5 inches and their results:

 3.5i => 3.5i 7/2 => 0i 7/2i => 0i 7i/2 => 0.1i 7i/2u => 3.5i 

Everything will be converted to basic units first. In the above example it is assumed that 1i equals 240u, and 1m equals 10p (thus 1m equals 33u). The value 7i/2 will be first handled as 7i/2m, then converted to 1680u/66u which is 25u, and this is approximately 0.1i.

As a conclusion, the safest way to specify measurements is to always attach a scaling indicator. If you want to multiply or divide by a certain scalar value, use u' as the unit for that value.

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## 5.4 Expressions

gtroff has most of operators common to other languages:

• Arithmetic: +' (addition), -' (subtraction), /' (division), *' (multiplication), %' (modulo).

gtroff only provides integer arithmetic. The internal type used for computing results is int', which is usually a 32bit signed integer.

• Comparison: <' (less than), >' (greater than), <=' (less than or equal), >=' (greater than or equal), =' (equal), ==' (the same as =').

• Logical: &' (logical and), :' (logical or).

• Unary operators: -' (negating, i.e. changing the sign), +' (just for completeness; does nothing in expressions), !' (logical not; this works only within if and while requests). See below for the use of unary operators in motion requests.

• Extrema: >?' (maximum), <?' (minimum). For example, 5>?3' yields 5'.

• Scaling: (c;e). Evaluate e using c as the default scaling indicator. If c is missing, ignore scaling indicators in the evaluation of e.

Parentheses may be used as in any other language. However, in gtroff they are necessary to ensure order of evaluation. gtroff has no operator precedence; expressions are evaluated left to right. This means that 3+5*4' is evaluated as if it were parenthesized like (3+5)*4', not as 3+(5*4)', as might be expected.

For many requests which cause a motion on the page, the unary operators work differently. The +' and -' operators then indicate a motion relative to the current position (down or up, respectively), and the |' operator indicates an absolute position on the page or input line. +' and -' are also treated differently by the following requests and escapes: bp, in, ll, lt, nm, nr, pl, pn, po, ps, rt, ti, \R, and \s. Here the plus and minus signs indicate increments resp. decrements.

See section 5.7.1 Setting Registers.

Due to the way arguments are parsed, spaces are not allowed in expressions, unless the entire expression is surrounded by parentheses.

See section 5.6.1.1 Request Arguments, and 5.20 Conditionals and Loops.

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## 5.5 Identifiers

Like any other language, gtroff has rules for properly formed identifiers. In gtroff, an identifier can be made up of almost any printable character, with the exception of the following characters:

• Whitespace characters (space, tabs, and newlines).

• Backspace (ASCII 0x08 resp. EBCDIC 0x16) and character code 0x01.

• The following input characters are invalid and will be ignored if groff runs on a machine based on ASCII, causing a warning message of type input' (see 5.30 Debugging, for more details): 0x00, 0x0B, 0x0D-0x1F, 0x80-0x9F.

And here are the invalid input characters if groff runs on an EBCDIC host: 0x00, 0x08, 0x09, 0x0B, 0x0D-0x14, 0x17-0x1F, 0x30-0x3F.

Currently, some of these reserved codepoints are used internally, thus making it non-trivial to extend gtroff to cover Unicode or other character sets resp. encodings which use characters of these ranges.

Note that invalid characters will be removed before parsing; an identifier foo, followed by an invalid character, followed by bar will be treated as foobar.

For example, any of the following is valid.

 br PP (l end-list @_ 

Note that identifiers longer than two characters with a closing bracket (]') in its name can't be accessed with escape sequences which expect an identifier as a parameter. For example, \[foo]]' will access the glyph foo', followed by ]', whereas \C'foo]'' really asks for glyph foo]'.

Escape: \A ident
Whether an identifier ident is valid in gtroff can be tested with the \A escape. It expands to the character 1 or 0 according to whether its argument (usually delimited by quotes) is or is not acceptable as the name of a string, macro, diversion, number register, environment, or font. It will return 0 if no argument is given. This is useful for looking up user input in some sort of associative table.

 \A'end-list' => 1 

See section 5.6.3 Escapes, for details on parameter delimiting characters.

Identifiers in gtroff can be any length, but, in some contexts, gtroff needs to be told where identifiers end and text begins (and in different ways depending on their length):

• Single character.

• Two characters. Must be prefixed with (' in some situations.

• Arbitrary length (gtroff only). Must be bracketed with [' and ]' in some situations. Any length identifier can be put in brackets.

Unlike many other programming languages, undefined identifiers are silently ignored or expanded to nothing.

See section 5.7.2 Interpolating Registers, and 5.19 Strings.

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## 5.6 Embedded Commands

Most documents need more functionality beyond filling, adjusting and implicit line breaking. In order to gain further functionality, gtroff allows commands to be embedded into the text, in two ways.

The first is a request which takes up an entire line, and does some large scale operation (e.g. break lines, start new pages).

The other is an escape which can be embedded anywhere in the text, or even as an argument to a request. Escapes generally do more minor operations like sub- and superscripts, print a symbol, etc.

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### 5.6.1 Requests

A request line begins with a control character, which is either a single quote ('', the no-break control character) or a period (.', the normal control character). These can be changed; see 5.12 Character Translations, for details. After this there may be optional tabs or spaces followed by an identifier which is the name of the request. This may be followed by any number of space-separated arguments.

To begin a line with a control character without it being interpreted, precede it with \&. This represents a zero width space, which means it will not affect the output.

In most cases the period is used as a control character. Several requests will cause a break implicitly; using the single quote control character will prevent this.

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#### 5.6.1.1 Request Arguments

Arguments to requests (and macros) are processed much like the shell: The line is split into arguments according to spaces. An argument which is intended to contain spaces can either be enclosed in quotes (single or double), or have the spaces escaped with backslashes.

Here are a few examples:

 .uh The Mouse Problem .uh "The Mouse Problem" .uh The\ Mouse\ Problem 

The first line is the uh macro being called with 3 arguments, The', Mouse', and Problem'. The latter two have the same effect or calling the uh macro with one argument, The Mouse Problem'.(5)

Note, however, that the ds request works differently. See section 5.19 Strings, for more details.

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### 5.6.2 Macros

gtroff has a macro facility for defining a series of lines which can be invoked by name. They are called in the same manner as requests -- arguments also may be passed in the same manner.

See section 5.21 Writing Macros, and 5.6.1.1 Request Arguments.

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### 5.6.3 Escapes

Escapes may occur anywhere in the input to gtroff. They usually begin with a backslash and are followed by a single character which indicates the function to be performed. The escape character can be changed; see 5.12 Character Translations.

Escape sequences which require an identifier as a parameter accept three possible syntax forms.

• The next single character is the identifier.

• If this single character is an opening parenthesis, take the following two characters as the identifier. Note that there is no closing parenthesis after the identifier.

• If this single character is an opening bracket, take all characters until a closing bracket as the identifier.

Examples:

 \fB \n(XX \*[TeX] 

Other escapes may require several arguments and/or some special format. In such cases the argument is traditionally enclosed in single quotes (and quotes are always used in this manual for the definitions of escape sequences). The enclosed text is then processed according to what that escape expects. Example:

 \l'1.5i$$bu'  Note that the quote character can be replaced with any other character which does not occur in the argument (even a newline or a space character) in the following escapes: \o, \b, and \X. This makes e.g.  A caf \o e\' in Paris => A café in Paris  possible, but it is better not to use this feature to avoid confusion. The following escapes sequences (which are handled similarly to characters since they don't take a parameter) are also allowed as delimiters: \%, \ ', \|, \^, \{, \}, \', \, \-, \_, \!, \?, \@, $$, \/, \,, \&, \~, \0, \a, \c, \d, \e, \E, \p, \r, \t, and \u. Again, don't use these if possible.

No newline characters as delimiters are allowed in the following escapes: \A, \Z, \C, and \w.

Finally, the escapes \D, \h, \H, \l, \L, \N, \R, \s, \S, \v, and \x can't use the following characters as delimiters:

• The digits 0-9.

• The (single-character) operators +-/*%<>=&:().'.

• The space, tab, and newline characters.

• All escape sequences except \%, \{, \}, \', \, \-, \_, \!, \@, \/, \c, \e, and \p.

To have a backslash (resp. the current escape character) appear in the output several escapes are defined: \\, \e or \E. These are very similar, and only differ with respect to being used in macros or diversions. See section 5.21.1 Copy-in Mode, and 5.25 Diversions, for more information.

See section 5.5 Identifiers, and 5.12 Character Translations.

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#### 5.6.3.1 Comments

Probably one of the most(6) common forms of escapes is the comment.

Escape: \" \arg\
Start a comment. Everything to the end of the input line is ignored.

This may sound simple, but it can be tricky to keep the comments from interfering with the appearance of the final output.

If the escape is to the right of some text or a request, that portion of the line will be ignored, but the space leading up to it will be noticed by gtroff. This only affects the .ds request.

One possibly irritating idiosyncracy is that tabs must not be used to line up comments. Tabs are not treated as white space between the request and macro arguments.

A comment on a line by itself will be treated as a blank line, because after eliminating the comment, that is all that remains:

 Test \" comment Test 

will produce

 Test Test 

As a consequence, it is common to start the line with .\" which will cause the line to be treated as an undefined request and thus ignored completely.

Another commenting scheme seen sometimes is three consecutive single quotes ("') at the beginning of a line. This works, but gtroff will give a warning about an undefined macro (namely "), which is harmless, but irritating.

Escape: \# \arg\
To avoid all this, gtroff has a new comment mechanism using the \# escape. This escape works the same as \" except that the newline is also ignored:

 Test \# comment Test 

will produce

 Test Test 

as expected.

For commenting away large blocks of text, the ig request may be useful.

See section 5.19 Strings.

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## 5.7 Registers

Numeric variables in gtroff are called registers. There are a number of built-in registers, supplying anything from the date to details of formatting parameters.

See section 5.5 Identifiers, for details on register identifiers.

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### 5.7.1 Setting Registers

Registers are defined resp. set via the nr request or the \R escape.

Request: nr ident value
Escape: \R ident value
Set number register ident to value. If ident doesn't exist, it will be created.

The argument to \R has to be enclosed in quotes usually. See section 5.6.3 Escapes, for details on parameter delimiting characters.

For example, the following two lines are equivalent:

 .nr a 1 \R'a 1' 

Both nr and \R have two additional special forms to increment resp. decrement a register.

Request: nr ident +value
Request: nr ident -value
Escape: \R ident +value
Escape: \R ident -value
Increment (decrement) register ident by value.

 .nr a 1 .nr a +1 \na => 2 

To assign the negated value of a register to another register, some care must be taken to get the desired result:

 .nr a 7 .nr b 3 .nr a -\nb \na => 4 .nr a (-\nb) \na => -3 

The surrounding parentheses prevent the interpretation of the minus sign as a decrementing operator. An alternative is to start the assignment with a 0':

 .nr a 7 .nr b -3 .nr a \nb \na => 4 .nr a 0\nb \na => -3 

Request: rr ident
Remove number register ident. If ident doesn't exist, the request is ignored.

Request: rnn ident1 ident2
Rename number register ident1 to ident2. If either ident1 or ident2 doesn't exist, the request is ignored.

Request: aln ident1 ident2
This request creates an alias ident1 for a number register ident2. The new name and the old name will be exactly equivalent. If ident1 is undefined, a warning of type reg' will be generated, and the request will be ignored. See section 5.30 Debugging, for information about warnings.

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### 5.7.2 Interpolating Registers

Numeric registers can be accessed via the \n escape.

Escape: \n ident
Interpolate number register ident. This means that the value of the register is expanded in-place while gtroff is parsing the input line.

 .nr a 5 .nr as \na+\na \n(as => 10 

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### 5.7.3 Auto-increment

Number registers can also be auto-incremented and auto-decremented. The increment resp. decrement factor can be specified with a third argument to the nr request or \R escape.

Request: nr ident value incr
Set number register ident to value; the increment for auto-incrementing is set to incr. Note that the \R escape doesn't support this notation.

To activate auto-incrementing, the escape \n has a special syntax form.

Escape: \n +ident
Escape: \n -ident
Before interpolating, increment resp. decrement ident by the auto-increment value as specified with the nr request (or the \R escape). If no auto-increment value has been specified, both syntax forms are identical to \n.

For example,

 .nr a 0 1 .nr xx 0 5 .nr foo 0 -2 \n+a, \n+a, \n+a, \n+a, \n+a .br \n-(xx, \n-(xx, \n-(xx, \n-(xx, \n-(xx .br \n+[foo], \n+[foo], \n+[foo], \n+[foo], \n+[foo] 

produces

 1, 2, 3, 4, 5 -5, -10, -15, -20, -25 -2, -4, -6, -8, -10 

To change the increment value without changing the value of a register, the following can be used:

 .nr a \na 10 

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### 5.7.4 Assigning Formats

When a register is used in the text of an input file (as opposed to part of an expression), it is textually replaced (or interpolated) with a representation of that number. This output format can be changed to a variety of formats (numbers, Roman numerals, etc.). This is done using the af request.

Request: af ident format
Change the output format of a number register. The first argument ident is the name of the number register to be changed, and the second argument format is the output format. The following output formats are available:

1
Decimal arabic numbers. This is the default format: 1, 2, 3, ....

0...0
Decimal numbers with as many digits as specified. So, 00' would result in printing numbers as 01, 02, 03, ....

In fact, any digit instead of zero will do; gtroff only counts how many digits are specified. As a consequence, af's default format 1' could be specified as 0' also (and exactly this is returned by the \g escape, see below).

I
Upper-case Roman numerals: 0, I, II, III, IV, ....

i
Lower-case Roman numerals: 0, i, ii, iii, iv, ....

A
Upper-case letters: A, B, C, ..., Z, AA, AB, ....

a
Lower-case letters: a, b, c, ..., z, aa, ab, ....

Omitting the number register format will cause a warning of type missing'. See section 5.30 Debugging, for more details. Specifying a nonexistent format causes an error.

The following example will produce 10, X, j, 010':

 .nr a 10 .af a 1 \" the default format \na, .af a I \na, .af a a \na, .af a 001 \na 

The largest number representable for the i' and I' formats is 39999 (resp. -39999); UNIX troff uses z' and w' to represent 10000 and 5000 in Roman numerals, and so does gtroff. Currently, the correct glyphs of Roman numeral five thousand and Roman numeral ten thousand (Unicode code points U+2182 and U+2181, respectively) are not available.

If ident doesn't exist, it will be created.

Changing the output format of a read-only register causes an error. It is necessary to first copy the register's value to a writeable register, then apply the af request to this other register.

Escape: \g ident
Return the current format of the specified register ident. For example, \ga' after the previous example would produce the string 000'. If the register hasn't been defined yet, nothing is returned.

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### 5.7.5 Built-in Registers

The following lists some built-in registers which are not described elsewhere in this manual. Any register which begins with a .' is read-only. A complete listing of all built-in registers can be found in 12. Register Index.

.H
Horizontal resolution in basic units.

.V
Vertical resolution in basic units.

dw
Day of the week (1-7).

dy
Day of the month (1-31).

mo
Current month (1-12).

year
The current year.

yr
The current year minus 1900. Unfortunately, the documentation of UNIX Version 7's troff had a year 2000 bug: It incorrectly claimed that yr contains the last two digits of the year. That claim has never been true of either traditional troff or GNU troff. Old troff input that looks like this:

 '\" The following line stopped working after 1999 This document was formatted in 19\n(yr. 

can be corrected as follows:

 This document was formatted in \n[year]. 

or, to be portable to older troff versions, as follows:

 .nr y4 1900+\n(yr This document was formatted in \n(y4. 

.c
c.
The current input line number. Register .c' is read-only, whereas c.' (a gtroff extension) is writable also, affecting both .c' and c.'.

ln
The current output line number after a call to the nm request to activate line numbering.

.x
The major version number. For example, if the version number is 1.03 then .x will contain 1'.

.y
The minor version number. For example, if the version number is 1.03 then .y will contain 03'.

.Y
The revision number of groff.

.g
Always 1. Macros should use this to determine whether they are running under GNU troff.

.A
If the command line option -a' is used to produce an ASCII approximation of the output, this is set to 1, zero otherwise. See section 2.1 Options.

.P
This register is set to 1 (and to 0 otherwise) if the current page is actually being printed, i.e., if the -o' option is being used to only print selected pages. See section 2.1 Options, for more information.

.T
If gtroff is called with the -T' command line option, the number register .T is set to 1, and zero otherwise. See section 2.1 Options.

Additionally, gtroff predefines a single (read/write) string register .T which contains the current output device (for example, latin1' or ps').

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## 5.8 Manipulating Filling and Adjusting

Various ways of causing breaks were given in 5.1.5 Implicit Line Breaks. The br request will likewise cause a break. Several other requests will also cause breaks, but implicitly. These are bp, ce, cf, fi, fl, in, nf, rj, sp, ti, and trf.

Request: br \arg\
Break the current line, i.e., the input collected so far will be emitted without adjustment.

If the no-break control character is used, no break will happen:

 a 'br b => a b 

Initially, gtroff will fill and adjust text to both margins. Filling can be disabled via the nf request and re-enabled with the fi request.

Request: fi \arg\
Activate fill mode (which is the default). This request implicitly enables adjusting; it will also cause a break in the text currently being filled. The number register .u is set to 1.

The fill mode status is associated with the current environment (see section 5.26 Environments).

Request: nf \arg\
Activate no-fill mode. Input lines are output as-is, retaining line breaks. The current line length will be ignored. This command implicitly disables adjusting; it also causes a break. The number register .u will be set to 0.

The fill mode status is associated with the current environment (see section 5.26 Environments).

Request: ad [mode]
Set adjusting mode.

Activation and deactivation of adjusting will be implicitly done with calls to the fi resp. nf requests.

mode can have one of the following values:

l
Adjust text to the left margin. This produces what is traditionally called ragged-right text.

r
Adjust text to the right margin, producing ragged-left text.

c
Center filled text. This is different to the ce request which only centers text without filling.

b
n
Justify to both margins. This is the default used by gtroff.

With no argument, gtroff will adjust lines in the same way it did before adjusting has been deactivated (with a call to na, for example).

 text .ad r text .ad c text .na text .ad \" back to centering text 

The current adjustment mode is available in the number register .j; it can be stored and subsequently used to set adjustment.

The adjustment mode status is associated with the current environment (see section 5.26 Environments).

Request: na \arg\
Disable adjusting. This request won't change the current adjustment mode: A call to ad afterwards will use the previous adjustment setting.

The adjustment mode status is associated with the current environment (see section 5.26 Environments).

Escape: \p \arg\
Adjust the current line and cause a break.

In most cases this will produce very ugly results, since gtroff doesn't have a sophisticated paragraph building algorithm (as TeX does, for example); instead, gtroff fills and adjusts a paragraph line by line:

  This is an uninteresting sentence. This is an uninteresting sentence.\p This is an uninteresting sentence. 

is formatted as

  This is an uninteresting sentence. This is an uninteresting sentence. This is an uninteresting sentence. 

Request: ss word_space_size [sentence_space_size]
Change the minimum size of a space between filled words. It takes its units as one twelfth of the space width parameter for the current font. Initially both the word_space_size and sentence_space_size are 12.

If two arguments are given to the ss request, the second argument sets the sentence space size. If the second argument is not given, sentence space size will be set to word_space_size. The sentence space size is used in two circumstances: if the end of a sentence occurs at the end of a line in fill mode, then both an inter-word space and a sentence space will be added; if two spaces follow the end of a sentence in the middle of a line, then the second space will be a sentence space. Note that the behaviour of UNIX troff will be exactly that exhibited by GNU troff if a second argument is never given to the ss request. In GNU troff, as in UNIX troff, a sentence should always be followed by either a newline or two spaces.

The number registers .ss and .sss hold the values of the parameters set by the first and second arguments of the ss request.

The word space and sentence space values are associated with the current environment (see section 5.26 Environments).

This request is ignored in nroff mode; it is also ignored if there is no parameter.

Request: ce [nnn]
Center text. While the .ad c' request will also center text, it has the side effect of filling the text. ce will not fill the text it affects. This request causes a break.

With no arguments, ce will center the next line of text. nnn specifies the number of lines to be centered. If the argument is zero or negative, centering is disabled.

The basic length for centering text is the line length (as set with the ll request) minus the indentation (as set with the in request). Temporary indentation is ignored.

A common idiom is to turn on centering for a large number of lines, and to turn off centering after text to be centered. This is useful for any request which takes a number of lines as an argument.

 .ce 1000 replace this with something more interesting ... .ce 0 

The .ce number register contains the number of lines remaining to be centered, as set by the ce request.

Request: rj [nnn]
Justify unfilled text to the right margin. Arguments are identical to the ce request. The .rj number register is the number of lines to be right-justified as set by the rj request. This request causes a line break.

 [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ]

## 5.9 Manipulating Hyphenation

As discussed in 5.1.2 Hyphenation, gtroff will hyphenate words. There are a number of ways to influence hyphenation.

Request: hy [mode]
Enable hyphenation. The request has an optional numeric argument, mode, to restrict hyphenation if necessary:

1
The default argument if mode is omitted. Hyphenate without restrictions. This is also the start-up value of gtroff.

2
Do not hyphenate the last word on a page or column.

4
Do not hyphenate the last two characters of a word.

8
Do not hyphenate the first two characters of a word.

Values in the previous table are additive. For example, the value 12 causes gtroff to neither hyphenate the last two nor the first two characters of a word.

The current hyphenation restrictions can be found in the number register .hy'.

The hyphenation mode is associated with the current environment (see section 5.26 Environments).

Request: nh \arg\
Disable hyphenation (i.e., set the hyphenation mode to zero). Note that the hyphenation mode of the last call to hy is not remembered.

The hyphenation mode is associated with the current environment (see section 5.26 Environments).

Request: hlm [nnn]
Set the maximum number of consecutive hyphenated lines to nnn. If this number is negative, there is no maximum. The default value is -1 if nnn is omitted. This value is associated with the current environment (see section 5.26 Environments). Only lines output from a given environment count towards the maximum associated with that environment. Hyphens resulting from \% are counted; explicit hyphens are not.

The current setting of hlm is available in the .hlm register. Also the number of immediately preceding consecutive hyphenated lines are available in the number register .hlc'.

Request: hw word1 word2 ...
Define how word1, word2, etc. are to be hyphenated. The words must be given with hyphens at the hyphenation points. For example:

 .hw in-sa-lub-rious 

Besides the space character, any character whose hyphenation code value is zero can be used to separate the arguments of hw (see the documentation for the hcode request below for more information). In addition, this request can be used more than once.

Hyphenation exceptions specified with the hw request are associated with the current hyphenation language; it will cause an error if there is no current hyphenation language.

This request is ignored if there is no parameter.

In old versions of troff there was a limited amount of space to store such information; fortunately, with gtroff, this is no longer a restriction.

Escape: \% \arg\
To tell gtroff how to hyphenate words on the fly, the \% escape, also known as the hyphenation character, can be used. Preceding a word with this character will prevent it from being hyphenated, putting it in a word will indicate to gtroff that the word may be hyphenated at that point. Note that this mechanism will only affect that one occurrence of the word; to change the hyphenation of a word for the entire document, use the hw request.

Request: hc [char]
Change the hyphenation character to char. This character will then work the same as the \% escape, and thus, no longer appear in the output. Without an argument, hc will reset the hyphenation character to be \% (the default) only.

The hyphenation character is associated with the current environment (see section 5.26 Environments).

Request: hpf pattern_file
Read in a file of hyphenation patterns. This file will be searched for in the same way as tmac.name' is searched for if the -mname' option is specified.

It should have the same format as the argument to the \patterns primitive in TeX (without using TeX's macro expansion); the letters appearing in this file are interpreted as hyphenation codes. A %' character in the patterns file introduces a comment that continues to the end of the line.

If no hpf request is specified (either in the document or in a macro package), gtroff won't hyphenate at all.

The set of hyphenation patterns is associated with the current language set by the hla request. The hpf request is usually invoked by the troffrc' or troffrc-end' file; by default, troffrc' loads hyphenation patterns for American English (in file hyphen.us').

hpf will cause an error if there is no current hyphenation language.

Request: hcode c1 code1 c2 code2 ...
Sets the hyphenation code of character c1 to code1, that of c2 to code2, etc. A hyphenation code must be a single input character (not a special character) other than a digit or a space. Initially each lower-case letter (a'-z') has its hyphenation set to itself, and each upper-case letter (A'-Z') has a hyphenation code which is the lower-case version of itself.

This request will be ignored if it has no parameter.

Request: hym [length]
Set the (right) hyphenation margin to length. If the current adjustment mode is not b', the line will not be hyphenated if it is shorter than length. Without argument, the hyphenation margin will be reset to its default value, which is 0. The default scaling indicator for this request is m. The hyphenation margin is associated with the current environment (see section 5.26 Environments).

A negative argument will reset the hyphenation margin to zero, emitting a warning of type range'.

The current hyphenation margin is available in the .hym register.

Request: hys [hyphenation_space]
Set the hyphenation space to hyphenation_space. If the current adjustment mode is b', don't hyphenate the line if it can be justified by adding no more than hyphenation_space extra space to each word space. Without argument, the hyphenation space is set to its default value, which is 0. The default scaling indicator for this request is m. The hyphenation space is associated with the current environment (see section 5.26 Environments).

A negative argument will reset the hyphenation space to zero, emitting a warning of type range'.

The current hyphenation space is available in the .hys register.

Request: shc [char]
Set the soft hyphen character to char. If the argument is omitted, the soft hyphen character will be set to the default character $$hy (this is the start-up value of gtroff also). The soft hyphen character is the character which will be inserted when a word is hyphenated at a line break. If the soft hyphen character does not exist in the font of the character immediately preceding a potential break point, then the line will not be broken at that point. Neither definitions (specified with the char request) nor translations (specified with the tr request) are considered when finding the soft hyphen character. Request: hla language Set the current hyphenation language to the string language. Hyphenation exceptions specified with the hw request and hyphenation patterns specified with the hpf request are both associated with the current hyphenation language. The hla request is usually invoked by the troffrc' or the troffrc-end' files; troffrc' sets the default language to us'. The current hyphenation language is available as a string in the read-only number register .hla'.  .ds curr_language \n[.hla] \*[curr_language] => us   [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ## 5.10 Manipulating Spacing Request: sp [distance] Space downwards distance. With no argument it will advance 1 line. A negative argument will cause gtroff to move up the page the specified distance. If the argument is preceded by a |' gtroff will move that distance from the top of the page. This request causes a line break. The default scaling indicator is v. Request: ls [nnn] Output nnn-1 blank lines after each line of text. With no argument gtroff will use the previous value before the last ls call.  .ls 2 \" This causes double-spaced output .ls 3 \" This causes triple-spaced output .ls \" Again double spaced  The line spacing is associated with the current environment (see section 5.26 Environments). The number register .L contains the current line spacing setting. Escape: \x spacing Sometimes, extra vertical spacing is only needed occasionally, e.g. to allow space for a tall construct (like an equation). The \x escape will do this. The escape is given a numerical argument, usually enclosed in quotes (like \x'3p''); the default scaling indicator is v. If this number is positive extra vertical space will be inserted below the current line. A negative number will add space above. If this escape is used multiple times on the same line, the maximum of the values is used. See section 5.6.3 Escapes, for details on parameter delimiting characters. The .a number register contains the most recent (nonnegative) extra vertical line space. Request: ns \arg\ Enable no-space mode. In this mode, spacing (either via sp or via blank lines) is disabled. The bp request to advance to the next page is also disabled, except if it is accompanied by a page number (see 5.16 Page Control, for more information). This mode will end when actual text is output or the rs request is encountered. This request is useful for macros which want to avoid that subsequent macros inadvertently insert some vertical space before the text starts (for example, to set up the first paragraph after a section header). It is associated with the current diversion level. Request: rs \arg\ Disable no-space mode. This request is associated with the current diversion level.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ## 5.11 Tabs and Fields A tab character (ASCII char 9, EBCDIC char 5) causes a horizontal movement to the next tab stop (much like it did on a typewriter). Escape: \t \arg\ This escape is a non-interpreted tab character. In copy mode (see section 5.21.1 Copy-in Mode), \t is the same as a real tab character. Request: ta [n1 n2 ... nn T r1 r2 ... rn] Change tab stop positions. This request takes a series of tab specifiers as arguments (optionally divided into two groups with the letter T') which indicate where each tab stop is to be (overriding any previous settings). Tab stops can be specified absolutely, i.e., as the distance from the left margin. For example, the following will set 6 tab stops every one inch.  .ta 1i 2i 3i 4i 5i 6i  Tab stops can also be specified relatively (using a leading +') which means that the specified tab stop will be set that distance from the previous tab stop. For example, the following is equivalent to the previous example.  .ta 1i +1i +1i +1i +1i +1i  gtroff supports an extended syntax to specify repeat values after the T' mark (these values are always taken as relative) -- this is the usual way to specify tabs set at equal intervals. The following is, yet again, the same as the previous examples. It does even more since it defines an infinite number of tab stops separated by one inch.  .ta T 1i  Now we are ready to interpret the full syntax given at the beginning: Set tabs at positions n1, n2, ..., nn and then set tabs at nn+r1, nn+r2, ..., nn+rn and then at nn+rn+r1, nn+rn+r2, ..., nn+rn+rn, and so on. Example: 4c +6c T 3c 5c 2c' is equivalent to 4c 10c 13c 18c 20c 23c 28c 30c ...'. The material in each tab column (i.e., the column between two tab stops) may be justified to the right or left or centered in the column. This is specified by appending R', L', or C' to the tab specifier. The default justification is L'. Example:  .ta 1i 2iC 2iR  Some notes: • The default unit of the ta request is m'. • A tab stop is converted into a non-breakable horizontal movement which can be neither stretched nor squeezed. For example,  .ds foo a\tb\tc .ta T 5i \*[foo]  creates a single line which is a bit longer than 10 inches (a string is used to show exactly where the tab characters are). Now consider the following:  .ds bar a\tb b\tc .ta T 5i \*[bar]  gtroff first converts the tab stops of the line into unbreakable horizontal movements, then splits the line after the second b' (assuming a sufficiently short line length). Usually, this isn't what the user wants. • Superfluous tabs (i.e., tab characters which do not correspond to a tab stop) are ignored except the first one which delimits the characters belonging to the last tab stop for right-justifying resp. centering. Consider the following example  .ds Z foo\tbar\tfoo .ds ZZ foo\tbar\tfoobar .ds ZZZ foo\tbar\tfoo\tbar .ta 2i 4iR \*[Z] .br \*[ZZ] .br \*[ZZZ] .br  which produces the following output:  foo bar foo foo bar foobar foo bar foobar  The first line right-justifies the second foo' relative to the tab stop. The second line right-justifies foobar'. The third line finally right-justifies only foo' because of the additional tab character which marks the end of the string belonging to the last defined tab stop. • Tab stops are associated with the current environment (see section 5.26 Environments). • Calling ta without an argument will unset all tab stops. • The start-up value of gtroff is T 0.5i'. This value is used even in nroff mode (contrary to UNIX nroff which has tab stops preset every 0.8i). The number register .tabs contains a string representation of the current tab settings suitable for use as an argument to the ta request.  .ds tab-string \n[.tabs] \*[tab-string] => T120u  Request: tc [fill-char] Normally gtroff will fill the space to the next tab stop with space. This can be changed with the tc request. With no argument gtroff will revert to using space, which is the default. The value of this tab repitition character is associated with the current environment (see section 5.26 Environments).  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ### 5.11.1 Leaders Sometimes it may may be desirable to use the tc request to fill a particular tab stop with a given character (for example dots in a table of contents), but also normal tab stops on the rest of the line. For this gtroff provides an alternate tab mechanism, called leaders which will do just that. A leader character (character code 1) behaves similarly to a tab character: It moves to the next tab stop. The only difference is that for this movement, the fill character defaults to a period character and not to space. Escape: \a \arg\ This escape is a non-interpreted leader character. In copy mode (see section 5.21.1 Copy-in Mode), \a is the same as a real leader character. Request: lc [fill-char] The character that will be repeated can be declared with the lc request. Without an argument, leaders will act the same as tabs (i.e., using space for filling). gtroff's start-up value is .'. The value of this leader repitition character is associated with the current environment (see section 5.26 Environments). For a table of contents, to name an example, tab stops may be defined so that the section number is one tab stop, the title is the second with the remaining space being filled with a line of dots, and then the page number slightly separated from the dots.  .ds entry 1.1\tFoo\a\t12 .lc . .ta 1i 5i +.25i \*[entry]  This produces  1.1 Foo.......................................... 12   [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ### 5.11.2 Fields Fields are a more general way of laying out tabular data. A field is defined as the data between a pair of delimiting characters. It contains substrings which are separated by padding characters. The width of a field is the distance on the input line from the position where the field starts to the next tab stop. A padding character inserts stretchable space similar to TeX's \hss command (thus it can even be negative) to make the sum of all substring lengths plus the stretchable space equal to the field width. If more than one padding character is inserted, the available space is evenly distributed among them. Request: fc [delim-char [padding-char]] Define a delimiting and a padding character for fields. If the latter is missing, the padding character defaults to a space character. If there is no argument at all, the field mechanism is disabled (which is the default). Note that contrary to e.g. the tab repitition character, delimiting and padding characters are not associated to the current environment (see section 5.26 Environments). Example:  .fc # ^ .ta T 3i #foo^bar^smurf# .br #foo^^bar^smurf#  and here the result:  foo bar smurf foo bar smurf   [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ## 5.12 Character Translations The control character (.') and the no-break control character ('') can be changed with the cc and c2 requests, respectively. Request: cc [c] Set the control character to c. With no argument the default control character .' is restored. The value of the control character is associated with the current environment (see section 5.26 Environments). Request: c2 [c] Set the no-break control character to c. With no argument the default control character '' is restored. The value of the no-break control character is associated with the current environment (see section 5.26 Environments). Request: eo \arg\ Disable the escape mechanism completely. After executing this request, the backslash character \' no longer starts an escape sequence. This request can be very helpful in writing macros since it is not necessary then to double the escape character. Here an example:  .\" This is a simplified version of the .\" .BR request from the man macro package .eo .de BR . ds result \& . while (\n[.] >= 2) \{\ . as result \fB\1\fR\2 . shift 2 . \} . if \n[.] .as result \fB\1 \*[result] . ft R .. .ec  Request: ec [c] Set the escape character to c. With no argument the default escape character \' is restored. It can be also used to re-enable the escape mechanism after an eo request. Note that changing the escape character globally will likely break macro packages since gtroff has no mechanism (like TeX) to intern' macros, i.e., to convert a macro definition into an internal form which is independent of its representation. If a macro is called, it will be executed literally. Escape: \e \arg\ This escape sequence prints the current escape character (which is the backslash character \' by default). A translation is a mapping of an input character to an output character. The default mappings are given in the font definition files for the specific output device (see section 8.2 Font Files); all mappings (both with tr and in the font definition files) occur at output time, i.e., the input character gets assigned the metric information of the mapped output character. Request: tr abcd... Translate character a to b, character c to d, etc. If there is an odd number of arguments, the last one will be translated to the space character. Some notes: • Special characters (\(xx, \[xxx], \C'xxx', \', \, \-, \_), characters defined with the char request, and numbered characters (\N'xxx') can be translated also. • The \e escape can be translated also. • Characters can be mapped onto the \% escape (but \% can't be mapped onto another character). • The following characters can't be translated: space (with one exception, see below), backspace, newline, leader (and \a), tab (and \t). • Translations are not considered for finding the soft hyphen character set with the shc request. • The character pair c\&' (this is an arbitrary character c followed by the zero width space character) will map this character to nothing.  .tr a\& foo bar => foo br  It is even possible to map the space character to nothing:  .tr aa \& foo bar => foobar  As shown in the example, the space character can't be the first character pair as an argument of tr. Additionally, it is not possible to map the space character to any other character; requests like .tr aa x' will undo .tr aa \&' instead. If justification is active, lines will be justified inspite of the empty' space character (but there is no minimal distance, i.e. the space character, between words). • After an output character has been constructed (this happens at the moment immediately before the character is appended to an output character list, either by direct output, in a macro, diversion, or string), it is no longer affected by tr. • Without an argument, the tr request is ignored. Request: trnt abcd... trnt is the same as the tr request except that the translations do not apply to text that is transparently throughput into a diversion with \!. See section 5.25 Diversions, for more information. For example,  .tr ab .di x \!.tm a .di .x  will print b'; if trnt is used instead of tr it will print a'.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ## 5.13 Troff and Nroff Mode Originally, nroff and troff were two separate programs, the former for tty output, the latter for everything else. With GNU troff, both programs are merged into one executable. Usually, a macro package can be used with both nroff and troff. Nevertheless, it is sometimes necessary to make a distinction between the two programs (resp. modes), and gtroff provides two built-in conditions n' and t' for the if, ie, and while requests to decide whether gtroff shall behave like nroff or like troff. Request: troff \arg\ Make the t' built-in condition true (and the n' built-in condition false) for if, ie, and while conditional requests. This is the default if gtroff (not groff) is started with the -R' switch to avoid loading of the start-up files troffrc' and troffrc-end'. Without -R', gtroff stays in troff mode if the output device is not a tty (e.g. ps'). Request: nroff \arg\ Make the n' built-in condition true (and the t' built-in condition false) for if, ie, and while conditional requests. This is the default if gtroff uses a tty output device; the code for switching to nroff mode is in the file tmac.tty' which will be loaded by the start-up file troffrc. See section 5.20 Conditionals and Loops, for more details on built-in conditions.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ## 5.14 Line Layout The following drawing shows the dimensions which gtroff uses for placing a line of output onto the page. They are labeled with the request which manipulates each dimension.   -->| in |<-- |<-----------ll------------>| +----+----+----------------------+----+ | : : : | +----+----+----------------------+----+ -->| po |<-- |<--------paper width---------------->|  These dimensions are: po Page offset -- this is the leftmost position of text on the final output, defining the left margin. in Indentation -- this is the distance from the left margin where text will be printed. ll Line length -- this is the distance from the left margin to right margin.  .in +.5i .ll -.5i A bunch of really boring text which should be indented from both margins. Replace me with a better (and more) example! .in -.5i .ll +.5i  Request: po [offset] Request: po +offset Request: po -offset Set horizontal page offset to offset (resp. increment or decrement the current value by offset). Note that this request does not cause a break, so changing the page offset in the middle of text being filled may not yield the expected result. The initial value is 1i if in troff mode, and 0 if in nroff mode (see section 5.13 Troff and Nroff Mode); the default scaling indicator is m (and not v as incorrectly documented in the original UNIX troff manual). The current page offset can be found in the built-in number register .o'. If po is called without an argument, the page offset is reset to the previous value before the last call to po.  .po 3i \n[.o] => 720 .po -1i \n[.o] => 480 .po \n[.o] => 720  Request: in [indent] Request: in +indent Request: in -indent Set indentation to indent (resp. increment or decrement the current value by indent). This request causes a break. Initially, there is no indentation. If in is called without an argument, the indentation is reset to the previous value before the last call to in. The default scaling indicator is m. The indentation is associated with the current environment. If a negative indentation value is specified (which is not allowed), gtroff emits a warning of type range' and sets the indentation to zero. The effect of in is delayed until a partially collected line (if it exists) is output. The current indentation (as set by in) can be found in the built-in number register .i'. Request: ti offset Request: ti +offset Request: ti -offset Temporarily indent the next output line by offset. If an increment or decrement value is specified, adjust the temporary indentation relative to the value set by the in request. This request causes a break; its value is associated with the current environment. The default scaling indicator is m. A call of ti without an argument is ignored. If the total indentation value is negative (which is not allowed), gtroff emits a warning of type range' and sets the temporary indentation to zero. Total indentation' is either offset if specified as an absolute value, or the temporary plus normal indentation, if offset is given as a relative value. The effect of ti is delayed until a partially collected line (if it exists) is output. The number register .in is the indentation that applies to the current output line. The difference between .i and .in is that the latter takes into account whether a partially collected line still uses the old indentation value resp. a temporary indentation value is active. Request: ll [length] Request: ll +length Request: ll -length Set the line length to length (resp. increment or decrement the current value by length). Initially, the line length is set to 6.5i. The effect of ll is delayed until a partially collected line (if it exists) is output. The default scaling indicator is m. If ll is called without an argument, the line length is reset to the previous value before the last call to ll. If a negative line length is specified (which is not allowed), gtroff emits a warning of type range' and sets the line length to zero. The line length is associated with the current environment. The current line length (as set by ll) can be found in the built-in number register .l. The number register .ll is the line length that applies to the current output line. Similar to .i and .in, the difference between .l and .ll is that the latter takes into account whether a partially collected line still uses the old line length value.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ## 5.15 Page Layout gtroff provides some very primitive operations for controlling page layout. Request: pl [length] Request: pl +length Request: pl -length Set the page length to length (resp. increment or decrement the current value by length). This is the length of the physical output page. The default scaling indicator is v. The current setting can be found in the built-in number register .p'. Note that this only specifies the size of the page, not the top and bottom margins. Those are not set by groff directly. See section 5.24 Traps, for further information on how to do this. Negative pl values are possible also, but not very useful: No trap is sprung, and each line is output on a single page (thus suppressing all vertical spacing). gtroff provides several operations which help in setting up top and bottom titles (or headers and footers). The tl request will print a title line, which consists of three parts: a left justified portion, a centered portion and a right justified portion. The argument to tl is specified as 'left'center'right'. The %' character is replaced with the current page number. This character can be changed with the pc request (see below). The title line is printed using its own line length, which is specified with the lt request. The current setting of this is available in the .lt number register. The pn request will change the page number of the next page. The only argument is the page number. The current page number is stored in the number register %. The number register .pn contains the number of the next page: either the value set by a pn request, or the number of the current page plus 1. The pc request will change the page number character (used by the tl request) to a different character. With no argument, this mechanism is disabled. See section 5.24 Traps.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ## 5.16 Page Control To stop processing the current page, and move to the next page, invoke the bp request. This request will also cause a break. It can also take an argument of what the next page should be numbered. The only difference between bp and pn is that pn does not cause a break or actually eject a page.  .de newpage 'bp 'sp .5i .tl 'left top'center top'right top' 'sp .3i ..  It is often necessary to force a certain amount of space before a new page occurs. This is most useful to make sure that there is not a single orphan line left at the bottom of a page. The ne request will ensure that there is a certain distance, specified by the first argument, before the next page is triggered (see 5.24 Traps, for further information). The default unit for ne is v and the default argument is 1v. For example, to make sure that no fewer than 2 lines get orphaned, do the following before each paragraph:  .ne 2 .ti +5n text  sv is similar to the ne request; it reserves the specified amount of vertical space. If the desired amount of space exists before the next trap (bottom page boundary), the space will be output immediately. If there is not enough space, it is stored for later output via the os request. The default argument is 1v and the default unit is v.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ## 5.17 Fonts gtroff has the ability to switch fonts at any point in the text. There are two ways to do this, via the ft request and the \f escape. Fonts are generally specified as upper-case strings, which are usually 1 to 4 characters representing an abbreviation or acronym of the font name. The basic set of fonts are R', I', B', and BI'. These are Times Roman, Italic, Bold, and Bold Italic. There is also at least one symbol font which contains various special symbols (Greek, mathematics). Such symbols fonts cannot be used directly, but should be used via an escape.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ### 5.17.1 Changing Fonts Font changes can be done either with the ft request or the \f request. With no arguments, it will switch to the previous font (also known as P').  eggs, bacon, .ft B spam .ft and sausage.  The \f escape is useful for changing fonts in the middle of words:  eggs, bacon, \fBspam\fP and sausage.  Both of the above examples will produce the same output. Note the usage of P' to indicate the previous font -- using \f it is not possible to omit this parameter. Sometimes, when putting letters of different fonts, more or less space at such boundaries are needed. There are two escapes to help with this. The \/ escape increases the width of the preceding character so that the spacing between that character and the following character will be correct if the following character is a Roman character. For example, if an italic f is immediately followed by a Roman right parenthesis, then in many fonts the top right portion of the f will overlap the top left of the right parenthesis. It is a good idea to use this escape sequence whenever an italic character is immediately followed by a Roman character without any intervening space. This small amount of space is also called italic correction. The \, escape modifies the spacing of the following character so that the spacing between that character and the preceding character will be correct if the preceding character is a Roman character. It is a good idea to use this escape sequence whenever a Roman character is immediately followed by an italic character without any intervening space. In analogy to above, this space could be called left italic correction, but this term isn't used widely. The ftr request will translate fonts; its syntax is  .ftr F G  which translates font F to font G. Whenever a font named F is referred to in a \f escape sequence, or in the ft, ul, bd, cs, tkf, special, fspecial, fp, or code requests, font G will be used. If G is missing, or equal to F then font F will not be translated.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ### 5.17.2 Font Families Due to the variety of fonts available, gtroff has added the concept of font families. Each of these families has four styles (R', I', B' and BI'). The fonts are specified as the concatenation of the font family and style. Specifying a font without the family part will cause gtroff to use that style of the current family. By default, gtroff uses the Times family. This way, it is possible to use the basic four fonts and to select a different font family on the command line. Font families can be switched with the fam request. The current font family is available in the number register .fam. This is a string-valued register.  spam, .fam H spam, .ft B spam, .fam T spam, .ft AR baked beans, .ft R and spam.   [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ### 5.17.3 Font Positions For the sake of old phototypesetters and compatability with old versions of troff, gtroff has the concept of font positions, on which various fonts are mounted. The last one or two are reserved for the symbol font(s). New fonts can be mounted with the fp request. These numeric positions can then be referred to with font changing commands. When gtroff starts it is using font number one.  .fp 1 H .fp 2 HI .fp 3 HB wink, wink, .ft 2 nudge, nudge, .ft .ft 3 say no more! .ft  Note that after these font changes have taken place, the original font is restored. The current font in use, as a font position, is available in number register .f. This can be useful to remember the current font, for later recall.  .nr save-font \n(.f ... lots 'o text ... .ft \n[save-font]  The number of the next free font position is available in the number register .fp. This is useful when mounting a new font, like so:  .fp \n[.fp] NEATOFONT  Fonts not listed in the DESC' file are automatically mounted on the next available font position when they are referenced. If a font is to be mounted explicitly with the fp request on an unused font position, it should be mounted on the first unused font position, which can be found in the .fp register. Although gtroff does not enforce this strictly, it will not allow a font to be mounted at a position whose number is much greater than that of any currently used position. The fp request has an optional third argument. This argument gives the external name of the font, which is used for finding the font description file. The second argument gives the internal name of the font which is used to refer to the font in gtroff after it has been mounted. If there is no third argument then the internal name will be used as the external name. This feature make it possible to use fonts with long names in compatibility mode.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ### 5.17.4 Using Symbols Symbols can be inserted by using a special escape sequence. This escape is simply the escape character (usually a backslash) followed by an identifier. The symbol identifiers have to be two or more characters, since single characters conflict with all the other escapes. The identifier can be either preceded by a parenthesis if it is two characters long, or surrounded by square brackets. So, the symbol for the mathematical Greek letter pi' can be produced either by \(*p or \[*p].  area = \(*p\fIr\fP\u2\d  The escape \C'xxx' will typeset the character named xxx. Normally it is more convenient to use \[xxx]. But \C has the advantage that it is compatible with recent versions of ditroff and is available in compatibility mode. The escape \N'n' will typeset the character with code n in the current font. n can be any integer. Most devices only have characters with codes between 0 and 255. If the current font does not contain a character with that code, special fonts will not be searched. The \N escape sequence can be conveniently used on conjunction with the char request:  .char \[phone] \f(ZD\N'37'  The code of each character is given in the fourth column in the font description file after the charset command. It is possible to include unnamed characters in the font description file by using a name of ---'; the \N escape sequence is the only way to use these. Each character has certain properties associated with it. These properties can be modified with the cflags request. The first argument is the the sum of the desired flags and the remaining arguments are the characters to have those properties. 1 the character ends sentences (initially characters .?!' have this property) 2 lines can be broken before the character (initially no characters have this property) 4 lines can be broken after the character (initially the characters -\(hy\(em' have this property) 8 the character overlaps horizontally (initially the characters \(ul\(rn\(ru' have this property) 16 the character overlaps vertically (initially character \(br' has this property) 32 an end of sentence character followed by any number of characters with this property will be treated as the end of a sentence if followed by a newline or two spaces; in other words the character is transparent for the purposes of end of sentence recognition -- this is the same as having a zero space factor in TeX (initially characters "')]*\(dg\(rq' have this property). New characters can be created with the char request. It is called as  .char c string  This defines character c to be string. Every time character c needs to be printed, string will be processed in a temporary environment and the result will be wrapped up into a single object. Compatibility mode will be turned off and the escape character will be set to \' while string is being processed. Any emboldening, constant spacing or track kerning will be applied to this object rather than to individual characters in string. A character defined by this request can be used just like a normal character provided by the output device. In particular other characters can be translated to it with the tr request; it can be made the leader character by the lc request; repeated patterns can be drawn with the character using the \l and \L escape sequences; words containing the character can be hyphenated correctly, if the hcode request is used to give the character a hyphenation code. There is a special anti-recursion feature: use of character within the character's definition will be handled like normal characters not defined with char. A character definition can be removed with the rchar request. Its arguments are the characters to be removed. This undoes the effect of a char request. See section 7.1 Special Characters.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ### 5.17.5 Artificial Fonts There are a number of requests for artificially creating fonts. These are largely vestigial remains from the days when output devices did not have a wide variety of fonts, and when nroff and troff were separate programs. These are no longer necessary in GNU troff. The ul request will print subsequent lines in italics on a device capable of it, or underline the text on a character output device. The single argument is the number of lines to be "underlined," with no argument, the next line will be underlined. The cu request is similar to ul ... The uf request will set the underline font used by ul and cu. The bd request artificially creates a bold font by printing each character twice, slightly offset. The first argument specifies the font to embolden, and the second is the number of basic units, minus one, by which the two characters will be offset. If the second argument is missing, emboldening will be turned off.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ### 5.17.6 Ligatures and Kerning The ligature mechanism can be switched on or off with the lg request; if the parameter is non-zero or missing, ligatures are enabled, otherwise disabled. Default is on. The current ligature mode can be found in the number register .lg (set to 1 if ligatures are enabled, 0 otherwise). If the font description file contains pairwise kerning information, characters from that font will be kerned. Kerning between two characters can be inhibited by placing \& between them. Kerning can be activated with the kern request. If the parameter is non-zero or missing, enable pairwise kerning, otherwise disable it. The number register .kern is set to 1 if pairwise kerning is enabled, 0 otherwise. Track kerning must be used with great care since it is usually considered bad typography if the reader notices the effect. The syntax of the tkf request is like this:  .tkf f s1 n1 s2 n2  Enable track kerning for font f. If the current font is f the width of every character will be increased by an amount between n1 and n2; if the current point size is less than or equal to s1 the width will be increased by n1; if it is greater than or equal to s2 the width will be increased by n2; if the point size is greater than or equal to s1 and less than or equal to s2 the increase in width is a linear function of the point size.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ## 5.18 Sizes gtroff uses two dimensions with each line of text, type size and vertical spacing. The type size is the height from the text baseline to the top of the tallest character (descenders may drop below this baseline). Vertical spacing is the amount of space gtroff allows for a line of text; normally, this is about 20% larger than the current type size. Ratios smaller than this can result in hard-to-read text; larger that this, it will spread the text out more vertically (useful for term papers). By default, gtroff uses 10 point type on 12 point spacing. The difference between type size and vertical spacing is known, by typesetters, as leading.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ### 5.18.1 Changing Type Sizes Using the ps request and the \s escape the type size can be changed. The vs request will change the vertical spacing. The default unit for the ps and vs requests are points. The number registers .s and .v contain the current type size and vertical spacing. These requests take parameters in units of points. It is possible to specify sizes as an absolute size, or as a relative change from the current size. The size 0 means go back to the previous size. With no argument it will also revert to the previous size.  snap, snap, .ps +2 grin, grin, .ps +2 wink, wink, \s+2nudge, nudge,\s+8 say no more! .ps 10  The \s escape may be called in a variety of ways. Much like other escapes there must be a way to determine where the argument ends and the text begins. Any of the following forms are valid: \sn Set the point size to n points. n must be either 0 or in the range 4 to 39. \s+n \s-n Increase resp. decrease the point size by n points. n must be exactly one digit. \s(nn Set the point size to nn points. nn must be exactly two digits. \s+(nn \s-(nn \s(+nn \s(-nn Increase resp. decrease the point size by nn points. nn must be exactly two digits. See section 5.18.2 Fractional Type Sizes, for yet another syntactical form of using the \s escape. Some devices may only have certain permissible sizes, in which case gtroff will round to the nearest permissible size.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ### 5.18.2 Fractional Type Sizes A scaled point is equal to 1/sizescale points, where sizescale is specified in the DESC' file (1 by default.) There is a new scale indicator z' which has the effect of multiplying by sizescale. Requests and escape sequences in gtroff interpret arguments that represent a point size as being in units of scaled points, but they evaluate each such argument using a default scale indicator of z'. Arguments treated in this way are the argument to the ps request, the third argument to the cs request, the second and fourth arguments to the tkf request, the argument to the \H escape sequence, and those variants of the \s escape sequence that take a numeric expression as their argument (see below). For example, suppose sizescale is 1000; then a scaled point will be equivalent to a millipoint; the request .ps 10.25' is equivalent to .ps 10.25z' and thus sets the point size to 10250 scaled points, which is equal to 10.25 points. It would make no sense to use the z' scale indicator in a numeric expression whose default scale indicator was neither u' nor z', and so gtroff disallows this. Similarly it would make no sense to use a scaling indicator other than z' or u' in a numeric expression whose default scale indicator was z', and so gtroff disallows this as well. There is also new scale indicator s' which multiplies by the number of units in a scaled point. So, for example, \n[.ps]s' is equal to 1m'. Be sure not to confuse the s' and z' scale indicators. The number register .s returns the point size in points as decimal fraction. There is also a new number register .ps that returns the point size in scaled points. The last-requested point size in scaled points is contained in the .psr number register. The last requested point size in points as a decimal fraction can be found in .sr. This is a string-valued register. \s[n] \s'n' Set the point size to n scaled points; n is a numeric expression with a default scale indicator of z'. \s[+n] \s[-n] \s+[n] \s-[n] \s'+n' \s'-n' \s+'n' \s-'n' Increase or resp. decrease the point size by n scaled points; n is a numeric expression with a default scale indicator of z'. See section 8.2 Font Files.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ## 5.19 Strings gtroff has string variables, which are entirely for user convenience (i.e. there are no built-in strings). They are defined via the ds request.  .ds UX \s-1UNIX\s0\u\s-3tm\s0\d  They are interpolated, or expanded in-place, via the \* escape:  The \*(UX Operating System  If the string named by the \* does not exist, the escape will be replaced by nothing. Caution: Unlike other requests, the second argument to the ds request takes up the entire line including trailing spaces. This means that comments on a line with such a request can introduce unwanted space into a string.  .ds UX \s-1UNIX\s0\u\s-3tm\s0\d \" UNIX trademark  Instead the comment should be put on another line or have the comment escape adjacent with the end of the string.  .ds UX \s-1UNIX\s0\u\s-3tm\s0\d\" UNIX trademark  To produce leading space the string can be started with a double quote. No trailing quote is needed; in fact, any trailing quote is included in your string.  .ds sign " Yours in a white wine sauce,  The as request will append a string to another string. It works similar to the ds request except that it appends the second argument onto the string named by the first argument.  .as sign " with shallots, onions and garlic,  Strings are not limited to a single line of text. A string can span several lines by escaping the newlines with a backslash. The resulting string will be stored without the newlines.  .ds foo lots and lots \ of text are on these \ next several lines  Rudimentary string manipulation routines are given with the substring and length requests. The former has the following syntax:  .substring xx n1 [n2]  It replaces the string in register xx with the substring defined by the indices n1 and n2. The first character in the string has index one. If n2 is omitted, it is taken to be equal to the string's length. If the index value n1 or n2 is negative or zero, it will be counted from the end of the string, going backwards: The last character has index 0, the character before the last character has index -1, etc. Here the syntax of the length request:  .length xx string  It computes the length of string and returns it in the number register xx (which is not necessarily defined before). See section 5.5 Identifiers, and 5.6.3.1 Comments.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ## 5.20 Conditionals and Loops In if and while requests, there are several more operators available: e o True if the current page is even or odd numbered (respectively). n True if the document is being processed in nroff mode. t True if the document is being processed in troff mode. 'xxx'yyy' True if the string xxx is equal to the string yyy. Other characters can be used in place of the single quotes. The strings are "formatted" before being compared. rxxx True if there is a number register named xxx. dxxx True if there is a string, macro, diversion, or request named xxx. cch True if there is a character ch available; ch is either an ASCII character or a special character (\(ch or \[ch]); the condition will also be true if ch has been defined by the char request.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ### 5.20.1 if-else gtroff has if-then-else constructs like other languages, although the formatting can be painful. The if request has the following syntax:  .if expr anything  where expr is the expression to be evaluated; anything (the remainder of the line) will be executed if expr evaluates to non-zero (true). anything will be interpreted as though it was on a line by itself. See section 5.4 Expressions, for more info. Here are some examples:  .if t .ls 2 \" double spacing in troff .if 0 .ab how'd this happen?  An if-then-else is written using two requests ie and el. The first request is the if' part and the latter is the else' part.  .ie .el  In many cases more than one request is to be executed as a result of any of these requests. This can be done using the \{ and \} escapes. The following example shows the possible ways to use these escapes (note the position of the opening and closing braces).  .ie t \{\ . ds lq  . ds rq '' .\} .el \ .\{\ . ds lq " . ds rq "\} .ds qq "  See section 5.4 Expressions.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ### 5.20.2 while gtroff provides a looping construct using the while request, which is used much like the if (and related) requests. The first argument is an expression which will be evaluated. The while request will interpret the remainder of the line until the expression evaluates to 0 or false.  .nr a 0 1 .while (\na<9) \&\n+a, \&\n+a  The preceding example produces:  1, 2, 3, 4, 5, 6, 7, 8, 9, 10  Note the usage of the \& escape to avoid a control character at the beginning of a line. The break request will break out of a while loop. Be sure not to confuse this with the br request (causing a line break). The continue request will finish the current iteration of a while loop, immediately restarting the next iteration. See section 5.4 Expressions.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ## 5.21 Writing Macros A macro is a collection of text and embedded commands which can be invoked multiple times. Macros are used for defining common operations. Macros are defined using the de request. This request takes a name for the macro as the first argument. Subsequent lines are copied into an internal buffer until the line .. is encountered. The optional second argument to de can change this ending token. Here a small example macro called P' which will cause a break and the insertion of some vertical space. It could be used to separate paragraphs.  .de P .br .sp .8v ..  The am request works similarly to de except it appends onto the macro named by the first argument. So, to make the previously defined P' macro actually do indented instead of block paragraphs, is is possible to add the necessary code to the existing macro like this:  .am P .ti +5n ..  Macros can be aliased with the als request.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ### 5.21.1 Copy-in Mode When gtroff reads in the text for a macro or diversion it copies the text (including request lines, but excluding escapes) into an internal buffer. Escapes will be converted into an internal form, except for \n, \, \*, \\ and \RET which are evaluated and inserted into the text where the escape was located. This is known as copy-in mode or copy mode. What this means is that you can specify when these escapes are to be evaluated (either at copy-in time or at the time of use) by insulating the escapes with an extra backslash. Compare this to the \def and \edef commands in TeX. For example, the following will result in the numbers 20 and being printed:  .nr x 20 .de y .nr x 10 \&\nx \&\\nx .. .y   [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ### 5.21.2 Parameters The arguments to a macro can be examined using a variety of escapes. The number of arguments is available in the . number register. Any individual argument can be retrieved with one of the following escapes: The escapes \n, \(nn and \[nnn] will result in the nth, nnth or nnnth argument. As usual, the first form only accepts a single number (larger than zero), the second only a two-digit number (larger or equal to 10), and the third any positive integer value (larger than zero). Macros can have an unlimited number of arguments. Note that due to copy-in mode, two backslashes should be used on these in actual use to prevent interpolation until the macro is actually invoked. The request shift will shift the arguments 1 position, or as many positions as specified by its argument. After executing this request, argument i will become argument i-n; arguments 1 to n will no longer be available. Shifting by negative amounts is currently undefined. In some cases it is convenient to use all of the arguments at once (for example, to pass the arguments along to another macro). The \* escape is the concatenation of all the arguments separated by spaces. A similar escape is \@, which is the concatenation of all the arguments with each surrounded by double quotes, and separated by spaces. The \0 escape is the name by which the current macro was invoked. The als request can make a macro have more than one name.  .de vl .ie \\n(.=1 .ds Vl Pre-Release Version .el .ds Vl Version \\3, \\4. ..  This would be called as  .vl Id: groff.texinfo,v 1.40 2000/06/18 10:13:51 wlemb Exp   See section 5.6.1.1 Request Arguments.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ## 5.22 Page Motions Motions up and down the page can be done with the sp request. However, this causes a break so that the actual effect is to move to the left margin and then to the specified location. The request mk can be used to mark a location on a page, for movement to later. This request takes a register name as an argument in which to store the current page location. With no argument it will store the location in an internal register. The results of this can be used later by the rt or the sp request. The rt request will return upwards to the location given in the register name given as an argument, with no argument it will return to the location marked with the mk request The following escapes give fine control of movements about the page. The \v'e' enables arbitrary vertical motion from the current location on the page. The argument e specifies the distance to move; positive is downwards and negative upwards. The default unit for this escape is vertical spaces, v's. Beware, however, that gtroff will leave text processing to continue wherever the motion ends, so to avoid interference with text processing, motions should be balanced. There are some special case escapes for vertical motion. \r move upwards 1v. \u move upwards .5v. \d move down .5v. Horizontal motions can be done via the \h'e' escape. The expression e indicates how far to move: positive is rightwards and negative leftwards. There are a number of special case escapes for horizontal motion: \SP an unbreakable and unpaddable (i.e. not expanded during filling) space. (Note: This is a backslash followed by a space.) \~ an unbreakable space that stretches like a normal inter-word space when a line is adjusted. \| a 1/6th em space. \^ a 1/12th em space. \0 a space the size of a digit. \& A zero width space. $$
Like \& except that it behaves like a character declared with the cflags request to be transparent for the purposes of end of sentence recognition.

A frequent need is to do horizontal movement based on the width of some arbitrary text (e.g. given as an argument to a macro). For that, there is the escape \w'text' which will interpolate to the width of the given text in basic units.

Font changes may occur in text which don't affect current settings.

After use, \w sets several registers:

st
sb
The highest and lowest point, respectively, in text.

rst
rsb
Like the st and sb registers, but takes account of the heights and depths of characters.

ct
is set according to what kinds of characters occur in text:

0
only short characters, no descenders or tall characters.

1
descender.

2
tall character.

3
both a descender and a tall character.

ssc
The amount of horizontal space (possibly negative) that should be added to the last character before a subscript.

skw
How far to right of the center of the last character in the \w argument, the center of an accent from a Roman font should be placed over that character.

\k

.k

 [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ]

## 5.23 Drawing Requests

gtroff provides a number of ways to draw lines and other figures on the page. Used in combination with the page motion commands (see 5.22 Page Motions, for more info), a wide variety of figures can be drawn. However, for complex drawings these operations can be quite cumbersome, and it may be wise to use graphic preprocessors like gpic or ggrn. See section 6.3 gpic, and 6.4 ggrn, for more information.

All drawing is done via escapes.

The \l escape will draw a line rightwards from the current location. The full syntax for this escape is like this:

 \l'lc' 

where l is the length of the line to be drawn, starting at the current location; positive numbers will draw to the right, and negative will draw towards the left. This can also be specified absolutely (i.e. with a leading |') which will draw back to the beginning of the line.

The optional second parameter c is a character to draw the line with. If this second argument is not specified, gtroff will use the underscore character.

To separate the two arguments (to prevent gtroff from interpreting a drawing character as a scaling indicator) use \&.

Here a small useful example:

 .de box \(br\\$*\(br\l'|0\(rn'\l'|0\(ul' ..  Note that this works by outputting a box rule (a vertical line), then the text given as an argument and then another box rule. Then the line drawing escapes both draw from the current location to the beginning of the input line. Vertical lines are drawn using the \L escape. Its parameters are specified similar to the \l escape. If the length is positive, the movement will be downwards, and upwards for negative values. The default character is the box rule character. As with the vertical motion escapes, text processing will blindly continue where the line ends. More flexible drawing functions are available via the \D escape. While the previous escapes will work on a character device, these escapes will not. \D'l dx dy' Draw a line from the current location to the relative point specified by (dx,dy). \D'c d' Draw a circle with a diameter of d with the leftmost point at the current position. \D'C d' Draw a solid circle with the same parameters as an outlined circle. \D'e dx dy' Draw an ellipse with a horizontal diameter of dx and a vertical diameter of dy with the leftmost point at the current position. \D'E dx dy' Draw a solid ellipse with the same parameters as an outlined ellipse. \D'a dx1 dy1 dx2 dy2' Draw an arc clockwise from the current location through the two specified locations (dx1,dy1) and (dx2,dy2). \D'~ dx1 dy1 dx2 dy2 ...' Draw a spline from the current location to (dx1,dy1) and then to (dx2,dy2), and so on. \D'f n' Set the shade of gray to be used for filling solid objects to n; n must be an integer between 0 and 1000, where 0 corresponds solid white and 1000 to solid black, and values in between correspond to intermediate shades of gray. This applies only to solid circles, solid ellipses and solid polygons. By default, a level of 1000 will be used. \D'p dx1 dy1 dx2 dy2 ...' Draw a polygon from the current location to (dx1,dy1) and then to (dx2,dy2) and so on. When the specified data points are exhausted, a line is drawn back to the starting point. \D'P dx1 dy1 dx2 dy2 ...' Draw a solid polygon with the same parameters as an outlined polygon. \D't n' Set the current line thickness to n machine units. A value of zero selects the smallest available line thickness. A negative value makes the line thickness proportional to the current point size (this is the default behaviour of ditroff). The \b escape will pile a sequence of characters vertically, and center it vertically on the current line. This can be used to build large brackets and braces.  \b'\(lt\(bv\(lk\(bv\(lb'  See section 8.1.3 Drawing Functions.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ## 5.24 Traps Traps are locations, which, when reached, will call a specified macro. These traps can occur at a given location on the page, at a given location in the current diversion, after a certain number of input lines or at the end of input.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ### 5.24.1 Page Location Traps Page location traps are frequently used for page headers and footers. The following is a simple example of this.  .de hd \" Page header 'sp .5i .tl 'Title''date' 'sp .3i .. .de fo \" Page footer 'sp 1v .tl ''%'' 'bp .. .wh 0 hd \" trap at top of the page .wh -1i fo \" trap one inch from bottom  The number register .t is the distance to the next trap. The location of a trap can be changed later on with the ch request. The first argument is the name of the macro to be invoked at the trap, and the second argument is the new location for the trap. This is useful for building up footnotes in a diversion to allow more space at the bottom of the page for them. The vpt request will enable vertical position traps if the argument is non-zero, disable them otherwise. Vertical position traps are traps set by the wh or dt requests. Traps set by the it request are not vertical position traps. The parameter that controls whether vertical position traps are enabled is global. Initially vertical position traps are enabled. The current setting of this is available in the number register .vpt. The number register .trunc contains the amount of vertical space truncated by the most recently sprung vertical position trap, or, if the trap was sprung by a ne request, minus the amount of vertical motion produced by the ne request. In other words, at the point a trap is sprung, it represents the difference of what the vertical position would have been but for the trap, and what the vertical position actually is. The number register .ne contains the amount of space that was needed in the last ne request that caused a trap to be sprung. Useful in conjunction with the .trunc register. See section 5.16 Page Control, for more information.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ### 5.24.2 Diversion Traps Traps can also be set within a diversion using the dt request. Like wh the first argument is the location of the trap and the second argument is the name of the macro to be invoked. The number register .t will still work within diversions. See section 5.25 Diversions, for more information.  [ < ] [ > ] [ << ] [ Up ] [ >> ] [Top] [Contents] [Index] [ ? ] ### 5.24.3 Input Line Traps The it request will set an input line trap. The format for calling this is  .it n name  where n is the number of lines of input which may be read before springing the trap, name is the macro to be invoked. Request lines are not counted as input lines. For example, one possible use is to have a macro which will print the next n lines in a bold font.  .de B .it B-end \\$1 .ft B .. .de B-end .ft R .. 

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### 5.24.4 End-of-input Traps

The em request will set a trap at the end of input. The macro specified as an argument will be executed after the last line of the input file has been processed.

For example, if the document had to have a section at the bottom of the last page for someone to approve it, the em request could be used.

 .de approval .ne 5v .sp |(\\n(.t-6v) .in +4i .lc _ .br Approved:\t\a .sp Date:\t\t\a .. .em approval 

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## 5.25 Diversions

In gtroff it is possible to divert text into a named storage area. Due to the similarity to defining macros it is sometimes said to be stored in a macro. This is used for saving text for output at a later time, which is useful for keeping blocks of text on the same page, footnotes, tables of contents and indices.

A diversion is initiated by the di request. Like the de request, it takes an argument of a macro name to divert subsequent text into. The da macro will append to an existing diversion.

di (resp. da) without an argument ends the diversion.

Diversions may be nested. The number register .z contains the name of the current diversion. The number register .d contains the current vertical place in the diversion. If not in a diversion it is the same as the register nl.

.h

After completing a diversion, the built-in number registers dn and dl contain the vertical and horizontal size of the diversion.

 .\" Center text both horizontally & vertically .de (c .br .nf .di @c .. .de )c .br .di .nr @s (((\\n(.tu-\\n(dnu)/2u)-1v) .sp \\n(@su .ce 1000 .nf . .br .ce 0 .sp \\n(@su .br .fi .rr @s .. 

Requests, macros and escapes are interpreted when read into a diversion. There are two ways to prevent this; either way will take the given text and transparently embed it into the diversion. The first method is to prefix the line with \!. This will cause the entire line to be transparently inserted into the diversion. This is useful for macros which shouldn't be invoked until the diverted text is actually output.

The other way is to surround the text by the \? escape, i.e.

 \?anything\? 

anything may not contain newlines; use \! to embed newlines in a diversion. The escape sequence \? is also recognized in copy mode and turned into a single internal code; it is this code that terminates anything. Thus the following example will print 4.

 .nr x 1 .nf .di d \?\\?\\\\?\\\\\\\\nx\\\\?\\?\? .di .nr x 2 .di e .d .di .nr x 3 .di f .e .di .nr x 4 .f 

The asciify request only exists in order to make certain gross hacks work with GNU troff. It unformats the diversion specified as an argument in such a way that ASCII characters that were formatted and diverted will be treated like ordinary input characters when the diversion is reread. For example, the following will set register n to 1.

 .tr @. .di x @nr\ n\ 1 .br .di .tr @@ .asciify x .x 

See section 5.21.1 Copy-in Mode.

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## 5.26 Environments

It happens frequently that some text should be printed in a certain format regardless of what may be in effect at the time, for example, in a trap invoked macro to print headers and footers. To solve this gtroff has environments in which text is processed. An environment contains most of the parameters that control text processing. It is possible to switch amongst these environments; by default gtroff processes text in environment 0. The following is the information kept in an environment.

• font parameters (size, family, style, character height and slant, space and sentence space size)

• page parameters (line length, title length, vertical spacing, line spacing, indentation, line numbering, hyphenation data)

• fill and adjust mode

• tab stops, tab and leader characters, escape character, no-break and hyphen indicators, margin character data

• partially collected lines

These environments may be given arbitrary names (see 5.5 Identifiers, for more info). Old versions of troff only had environments named 0', 1' and 2'.

The ev request will switch to another environment. The single argument is the name of the environment to switch to. With no argument gtroff will switch back to the previous environment. There is no limit on the number of named environments; they will be created the first time that they are referenced. The .ev register contains the name or number of the current environment. This is a string-valued register.

Note that a call to ev (with argument) will push the previously active environment onto a stack. If, say, environments foo', bar', and zap' are called (in that order), the first ev request without parameter will switch back to environment bar' (which will be popped off the stack), and a second call will switch back to environment foo'.

Here is another example:

 .ev footnote-env .fam N .ps 6 .vs 8 .ll -.5i .ev ... .ev footnote-env \(dg Note the large, friendly letters. .ev 

To copy an environment into the current one, use the evc request, which takes the name of the environment to copy from as an argument.

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## 5.27 I/O

The so request will read in the file given as an argument and include it in place of the so request. This is quite useful for large documents, i.e. keeping each chapter in a separate file. See section 6.7 gsoelim, for more information.

The mso request is the same as the so request except that the file is searched for in the same directories as tmac.name' is searched for when the -mname' option is specified.

The cf and trf requests are to include a file. It will transparently output the contents of file filename. Each line is output as it were preceded by \!; however, the lines are not subject to copy mode interpretation. If the file does not end with a newline, then a newline will be added. For example, to define a macro x containing the contents of file f', use

 .di x .trf f .di 

The request .cf filename, when used in a diversion, will embed in the diversion an object which, when reread, will cause the contents of filename to be transparently copied through to the output. In UNIX troff, the contents of filename is immediately copied through to the output regardless of whether there is a current diversion; this behaviour is so anomalous that it must be considered a bug. This request causes a line break.

With trf, unlike cf, the file cannot contain characters such as NUL that are not valid gtroff input characters (see section 5.5 Identifiers). This request causes a line break.

The nx request will force gtroff to continue processing of the file specified as an argument.

The rd request will read from standard input, and include what is read as though it were part of the input file. Text is read until a blank line is encountered.

Using these two requests it is easy to set up form letters. The form letter template is constructed like this:

 .ce \*(td .sp 2 .nf .rd .sp .rd .fi Body of letter. .bp .nx repeat.let 

When this is run, the following file should be redirected in. Note that requests included in this file are executed as though they were part of the form letter. The last block of input is the ex requests which tells groff to stop processing. If this was not there, groff would not know when to stop.

 Trent A. Fisher 708 NW 19th Av., #202 Portland, OR 97209 Dear Trent, Len Adollar 4315 Sierra Vista San Diego, CA 92103 Dear Mr. Adollar, .ex 

pi

The sy request will allow arbitrary system commands to be executed from within a gtroff document. The output is not saved anyplace, so it is up to the user to do so.

For example, the following example will introduce the current time into a document:

 .sy perl -e 'printf ".nr H %d\\n.nr M %d\\n.nr S %d\\n",\ (localtime(time))[2,1,0]' > /tmp/x\n[$$] .so /tmp/x\n[$$] .sy rm /tmp/x\n[] \nH:\nM:\nS 

Note that this works by having the perl script (run by sy) print out the nr requests which will set the number registers H', M' and S', and then reads those commands in with the so request.

The systat number register contains the return value of the system() function executed by the last sy request.

The open request will open a file (specified as the second argument) for writing and associate the stream (specified as the first argument) with it.

The opena is like open, but if the file exists, append to it instead of truncating it.

The write request will write to the file associated with the stream specified by the first argument. The stream must previously have been the subject of an open request. The remainder of the line is interpreted as the ds request reads its second argument: A leading "' will be stripped, and it will be read in copy-in mode.

The close request will close the stream specified by the first argument; stream will no longer be an acceptable argument to the write request.

The \V escape will interpolate the contents of the specified environment variable, as returned by the function getenv. The argument to \V is specified as an identifier, i.e. \Vx', \V(xx' or \V[xxx]'. \V is interpreted in copy-in mode.

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## 5.28 Postprocessor Access

There are two escapes which will allow information to be directly given to the postprocessor. This is particularly useful for embedding POSTSCRIPT into the final document.

The \X escape will embed its argument into the gtroff output preceded with x X'.

The \Y escape is called with an identifier (i.e. \Yx, \Y(xx or \Y[xxx]). This is approximately equivalent to \X'\*[xxx]''. However, the contents of the string or macro xxx are not interpreted; also it is permitted for xxx to have been defined as a macro and thus contain newlines (it is not permitted for the argument to \X to contain newlines). The inclusion of newlines requires an extension to the UNIX troff output format, and will confuse drivers that do not know about this extension.

See section 7. Output Devices.

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## 5.29 Miscellaneous

This section documents parts of gtroff which cannot (yet) be categorized elsewhere in this manual.

Line numbers can be printed in the left margin using the nm request. The first argument is the line number of the next output line; this defaults to 1. The second argument indicates on which lines numbers will be printed, i.e. 5 means put line numbers on every 5 lines; this defaults to 1. The third argument is the space to be left between the number and the text; this defaults to 1. The fourth argument is the indentation of the line numbers. Without arguments, line numbers are turned off.

The nn request will temporarily turn off line numbering. The first argument is the number of lines not to be numbered; this defaults to 1.

Margin characters can be automatically printed to the right of the text with the mc request. The first argument is the character to be printed, and the second argument is the distance away from the main body text. With no arguments the margin characters are turned off. If this occurs before a break, no margin character will be printed.

This is quite useful for indicating text that has changed, and, in fact, there are programs available for doing this (they are called nrchbar and changebar and can be found in any comp.sources.unix' archive.

The primary reason for the existence of lf is to make debugging documents which are split into many files, which are then put together with soelim and other preprocessors. The first argument is the name of the file and the second argument is the input line number in that file. This way gtroff can produce error messages which are intelligible to the user.

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## 5.30 Debugging

gtroff is not easy to debug, but there are some useful features and strategies for debugging.

• The tm request will send output to the standard error stream; this is very useful for printing debugging output.

• When doing something involved it is useful to leave the debugging statements in the code and have them turned on by a command line flag.

 .if \n(DB .tm debugging output 

To activate these statements say

 groff -rDB=1 file 

• The ab request is similar to the tm request, except that it will cause gtroff to stop processing. With no argument it will print User Abort'.

• The ex request will also cause gtroff to stop processing if encountered at the topmost level; see also 5.27 I/O.

• If it is known in advance that there will be many errors and no useful output, gtroff can be forced to suppress formatted output with the -z' flag.

• The pm request will dump out the entire symbol table.

• The pnr request will print the names and contents of all currently defined number registers on stderr.

• The ptr request will print the names and positions of all traps (not including input line traps and diversion traps) on stderr. Empty slots in the page trap list are printed as well, because they can affect the priority of subsequently planted traps.

• The fl request instructs gtroff to flush its output immediately. The intention is that this be used when using gtroff interactively. There is little other use for it. This request causes a line break.

• The backtrace request will print a backtrace of the input stack to the standard error stream.

• gtroff has command line options for printing out more warnings (-w') and for printing backtraces (-b') when a warning or an error occurs. The most verbose level of warnings is -ww'.

• The warn request controls the level of warnings checked for. The only argument is the sum of the numbers associated with each warning that is to be enabled; all other warnings will be disabled. The number associated with each warning is listed below. For example, .warn 0 will disable all warnings, and .warn 1 will disable all warnings except that about missing characters. If an argument is not given, all warnings will be enabled. The number register .warn contains the current warning level.

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### 5.30.1 Warnings

The warnings that can be given to gtroff are divided into the following categories. The name associated with each warning is used by the -w' and -W' options; the number is used by the warn request and by the .warn register.

char'
1'
Non-existent characters. This is enabled by default.

number'
2'
Invalid numeric expressions. This is enabled by default. See section 5.4 Expressions.

break'
4'
In fill mode, lines which could not be broken so that their length was less than the line length. This is enabled by default.

delim'
8'
Missing or mismatched closing delimiters.

el'
16'
Use of the el request with no matching ie request. See section 5.20.1 if-else.

scale'
32'
Meaningless scaling indicators.

range'
64'
Out of range arguments.

syntax'
128'
Dubious syntax in numeric expressions.

di'
256'
Use of di or da without an argument when there is no current diversion.

mac'
512'
Use of undefined strings, macros and diversions. When an undefined string, macro or diversion is used, that string is automatically defined as empty. So, in most cases, at most one warning will be given for each name.

reg'
1024'
Use of undefined number registers. When an undefined number register is used, that register is automatically defined to have a value of 0. A definition is automatically made with a value of 0. So, in most cases, at most one warning will be given for use of a particular name.

tab'
2048'
Use of a tab character where a number was expected.

right-brace'
4096'
Use of \} where a number was expected.

missing'
8192'
Requests that are missing non-optional arguments.

input'
16384'
Illegal input characters.

escape'
32768'
Unrecognized escape sequences. When an unrecognized escape sequence is encountered, the escape character is ignored.

space'
65536'
Missing space between a request or macro and its argument. This warning will be given when an undefined name longer than two characters is encountered, and the first two characters of the name make a defined name. The request or macro will not be invoked. When this warning is given, no macro is automatically defined. This is enabled by default. This warning will never occur in compatibility mode.

font'
131072'
Non-existent fonts. This is enabled by default.

all'
All warnings except di', mac' and reg'. It is intended that this covers all warnings that are useful with traditional macro packages.

w'
All warnings.

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## 5.31 Implementation Differences

GNU troff has a number of features which cause incompatibilities with documents written with old versions of troff.

Long names cause some incompatibilities. UNIX troff will interpret

 .dsabcd 

as defining a string ab' with contents cd'. Normally, GNU troff will interpret this as a call of a macro named dsabcd. Also UNIX troff will interpret \*[ or \n[ as references to a string or number register called ['. In GNU troff, however, this will normally be interpreted as the start of a long name. In compatibility mode GNU troff will interpret these things in the traditional way. In compatibility mode, however, long names are not recognized. Compatibility mode can be turned on with the -C' command line option, and turned on or off with the cp request. The number register .C is 1 if compatibility mode is on, 0 otherwise.

GNU troff does not allow the use of the escape sequences \|, \^, \&, \}, \{, \SP, \', \, \-, \_, \!, \%, and \c in names of strings, macros, diversions, number registers, fonts or environments; UNIX troff does. The \A escape sequence (see section 5.5 Identifiers) may be helpful in avoiding use of these escape sequences in names.

Fractional point sizes cause one noteworthy incompatibility. In UNIX troff the ps request ignores scale indicators and thus

 .ps 10u 

will set the point size to 10 points, whereas in GNU troff it will set the point size to 10 scaled points. See section 5.18.2 Fractional Type Sizes, for more information.

In GNU troff there is a fundamental difference between unformatted, input characters, and formatted, output characters. Everything that affects how an output character will be output is stored with the character; once an output character has been constructed it is unaffected by any subsequent requests that are executed, including bd, cs, tkf, tr, or fp requests. Normally output characters are constructed from input characters at the moment immediately before the character is added to the current output line. Macros, diversions and strings are all, in fact, the same type of object; they contain lists of input characters and output characters in any combination. An output character does not behave like an input character for the purposes of macro processing; it does not inherit any of the special properties that the input character from which it was constructed might have had. For example,

 .di x \\\\ .br .di .x 

will print \\' in GNU troff; each pair of input backslashes is turned into one output backslash and the resulting output backslashes are not interpreted as escape characters when they are reread. UNIX troff would interpret them as escape characters when they were reread and would end up printing one \'. The correct way to obtain a printable backslash is to use the \e escape sequence: This will always print a single instance of the current escape character, regardless of whether or not it is used in a diversion; it will also work in both GNU troff and UNIX troff. To store, for some reason, an escape sequence in a diversion that will be interpreted when the diversion is reread, either use the traditional \! transparent output facility, or, if this is unsuitable, the new \? escape sequence.

See section 5.25 Diversions, for more information.

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## 5.32 Summary

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This document was generated by root l2-hrz on May, 9 2001 using texi2html