GTROFF(1)

NAME
gtroff - format documents

SYNOPSIS
gtroff [-abivzCER] [-w name] [-W name] [-d cs] [-f fam] [-m name] [-n num] [-o list] [-r cn] [-T name] [-F dir] [-M dir] [-H file] [ files... ]

DESCRIPTION
This manual page describes the GNU version of troff, which is part of the groff document formatting system. It is highly compatible with Unix troff. Usually it should be invoked using the groff command, which will also run preprocessors and postprocessors in the appropriate order and with the appropriate options.

OPTIONS

-a  Generate an ASCII approximation of the typeset output.

-b  Print a backtrace with each warning or error message. This backtrace should help track down the cause of the error. The line numbers given in the backtrace may not always correct: troff's idea of line numbers gets confused by as or am requests.

-i  Read the standard input after all the named input files have been processed.

-v  Print the version number.

-wname
    Enable warning name. Available warnings are described in the Warnings subsection below. Multiple -w options are allowed.

-Wname
    Inhibit warning name. Multiple -W options are allowed.

-E  Inhibit all error messages.

-z  Suppress formatted output.

-C  Enable compatibility mode.

-dcs
-dname=s
    Define c or name to be a string s; c must be a one letter name.

-ffam
    Use fam as the default font family.

-mname
    Read in the file tmac.name. Normally this will be searched for in /usr/lib/groff/tmac.

-R  Don't load troffrc.

-nnum
    Number the first page num.

-olist
    Output only pages in list, which is a comma-separated list of page ranges; n means print page n, m-n means print every page between m and n, -n mans print every page up to n, n- means print every page from n.

-rcn
-rname=n
    Set number register c or name to n; c must be a one character name; n can be any troff numeric expression.

-Tname
    Prepare output for device name, rather than the default ps.

-Fdir
    Search dir for subdirectories devname (name is the name of the device) for the DESC file and font files before the normal /usr/lib/groff/font.

-Hfile
    Read hyphenation patterns from file, rather than the default /usr/lib/groff/hyphen.

-Mdir
    Search directory dir for macro files before the normal /usr/lib/groff/tmac.

USAGE
Only the features not in Unix troff are described here.

  Long names
The names of number registers, fonts, strings/macros/diversions, special characters can be of any length. In escape sequences, where you can use (xx for a two character name, you can use [xxx] for a name of arbitrary length:

\[xxx]
    Print the special character called xxx.

\f[xxx]
    Set font xxx.

\*[xxx]
    Interpolate string xxx.

\n[xxx]
    Interpolate number register xxx.

  Fractional pointsizes
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 troff interpret arguments that represent a pointsize 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.

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 so sets the pointsize to 10250 scaled points, which is equal to 10.25 points.

The number register \n(.s returns the pointsize in points as decimal fraction. There is also a new number register \n[.ps] that returns the pointsize in scaled 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 troff disallows this. Similarily 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 troff 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.

  Numeric expressions

Spaces are permitted in a number expression within parentheses.

M indicates a scale of 100ths of an em.

e1>?e2
    The maximum of e1 and e2.

e1<?e2
    The minimum of e1 and e2.

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

  New escape sequences

\A'anything'
    This expands to 1 or 0 according as anything is or is not acceptable as the name of a string, macro, diversion, number register, environment or font. It will return 0 if anything is empty. This is useful if you want to lookup user input in some sort of associative table.

\C'xxx'
    Typeset character named xxx. Normally it is more convenient to use \[xxx]. But \C has the advantage that it is compatible with recent versions of UNIX and is available in compatibility mode.

\E  This is equivalent to an escape character, but it's not interpreted in copy-mode. For example, strings to start and end superscripting could be defined like this:

        .ds { \v'-.3m'\s'\En[.s]*6u/10u'
        .ds } \s0\v'.3m'

    The use of \E ensures that these definitions will work even if \*{ gets interpreted in copy-mode (for example, by being used in a macro argument.)

\N'n'
    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.

\R'name ±n'
    This has the same effect as

        .nr name ±n

\s(nn
\s±(nn
    Set the point size to nn points; nn must be exactly two digits.

\s[±n]
\s±[n]
\s'±n'
\s±'n'
    Set the point size to n scaled points; n is a numeric expression with a default scale indicator of z.

\Yx
\Y(xx
\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.

\Z'anything'
    Print anything and then restore the horizontal and vertical position; anything may not contain tabs or leaders.

\$0 The name by which the current macro was invoked. The als request can make a macro have more than one name.

\$* In a macro, the concatenation of all the arguments separated by spaces.

\$@ In a macro, the concatenation of all the arguments with each surrounded by double quotes, and separated by spaces.

\$(nn
\$[nnn]
    In a macro, this gives the nn-th or nnn-th argument. Macros can have a unlimited number of arguments.

\?anything\?
    When used in a diversion, this will transparently embed anything in the diversion. anything is read in copy mode. When the diversion is reread, anything will be interpreted. anything may not contain newlines; use \! if you want to embed newlines in a diversion. The escape sequence \? is also recognised in copy mode and turned into a single internal code; it is this code that terminates anything. Thus
        .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

    will print 4.

\/  This 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 producing f), which is ugly. Inserting \/ produces f) and avoids this problem. 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 modifies the spacing of the following character so that the spacing between that character and the preceding character will correct if the preceding character is a roman character. For example, inserting \, between the parenthesis and the f changes (f to (f. 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.

\)  Like \& except that it behaves like a character declared with the cflags request to be transparent for the purposes of end of sentence recognition.

\~  This produces an unbreakable space that stretches like a normal inter-word space when a line is adjusted.

\#  Everything up to and including the next newline is ignored. This is interpreted in copy mode. This is like \% except that \% does not ignore the terminating newline.

  New requests

.aln xx yy
    Create an alias xx for number register object named yy. The new name and the old name will be exactly equivalent. If yy is undefined, a warning of type reg will be generated, and the request will be ignored.

.als xx yy
    Create an alias xx for request, string, macro, or diversion object named yy. The new name and the old name will be exactly equivalent (it is similar to a hard rather than a soft link). If yy is undefined, a warning of type mac will be generated, and the request will be ignored. The de, am, di, da, ds, and as requests only create a new object if the name of the macro, diversion or string diversion is currently undefined or if it is defined to be a request; normally they modify the value of an existing object.

.asciify xx
    This request only exists in order to make it possible to make certain gross hacks work with GNU troff. It `unformats' the diversion xx in such a way that ASCII characters that were formatted and diverted into xx will be treated like ordinary input characters when xx is reread. For example, this

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

    will set register n to 1.

.backtrace
    Print a backtrace of the input stack on stderr.

.break
    Break out of a while loop. See also the while and continue requests. Be sure not to confuse this with the br request.

.cflags n c1 c2...
    Characters c1, c2,... have properties determined by n, which is ORed from the following:

    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 characters -\(hy\(em have this property);

    8   the character overlaps horizontally (initially 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).

.char c string
    Define 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.

.chop xx
    Chop the last character off macro, string, or diversion xx. This is useful for removing the newline from the end of diversions that are to be interpolated as strings.

.close stream
    Close the stream named stream; stream will no longer be an acceptable argument to the write request. See the open request.

.continue
    Finish the current iteration of a while loop. See also the while and break requests.

.cp n
    If n is non-zero or missing, enable compatibility mode, otherwise disable it. In compatibility mode, long names are not recognised, and the incompatibilities caused by long names do not arise.

.do xxx
    Interpret .xxx with compatibility mode disabled. For example,

        .do fam T

    would have the same effect as

        .fam T

    except that it would work even if compatibility mode had been enabled. Note that the previous compatibility mode is restored before any files sourced by xxx are interpreted.

.fam xx
    Set the current font family to xx. The current font family is part of the current environment. See the description of the sty request for more information on font families.

.fspecial f s1 s2...
    When the current font is f, fonts s1, s2,... will be special, that is, they will searched for characters not in the current font. Any fonts specified in the special request will be searched before fonts specified in the fspecial request.

.ftr f g
    Translate font f to g. Whenever a font named f is referred to in \f escape sequence, or in the ft, ul, bd, cs, tkf, special, fspecial, fp, or sty requests, font g will be used. If g is missing, or equal to f then font f will not be translated.

.hcode c1 code1 c2 code2...
    Set the hyphenation code of character c1 to code1 and that of c2 to code2. 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 has a hyphenation code, which is itself, and each upper-case letter has a hyphenation code which is the lower case version of itself. Hyphenation is controlled by a file of hyphenation patterns (normally /usr/lib/groff/hyphen); this file should have the same format as the argument to the \patterns primitive in TeX; the letters appearing in this file are interpreted as hyphenation codes.

.hlm n
    Set the maximum number of consecutive hyphenated lines to n. If n is negative, there is no maximum. The default value is -1. This value is associated with the current environment. Only lines output from an environment count towards the maximum associated with that environment. Hyphens resulting from \% are counted; explicit hyphens are not.

.hym n
    Set the hyphenation margin to n: when the current adjustment mode is not b, the line will not be hyphenated if the line is no more than n short. The default hyphenation margin is 0. The default scaling indicator for this request is m. The hyphenation margin is associated with the current environment. The current hyphenation margin is available in the \n[.hym] register.

.hys n
    Set the hyphenation space to n: when the current adjustment mode is b don't hyphenate the line if the line can be justified by adding no more than n extra space to each word space. The default hyphenation space is 0. The default scaling indicator for this request is m. The hyphenation space is associated with the current environment. The current hyphenation space is available in the \n[.hys] register.

.kern n
    If n is non-zero or missing, enable pairwise kerning, otherwise disable it.

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

.nroff
    Make the n built-in condition true and the t built-in condition false. This can be reversed using the troff request.

.open stream filename
    Open filename for writing and associate the stream named stream with it. See also the close and write requests.

.opena stream filename
    Like open, but if filename exists, append to it instead of truncating it.

.pnr
    Print the names and contents of all currently defined number registers on stderr.

.ptr
    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.

.rchar c1 c2...
    Remove the definitions of characters c1, c2,... This undoes the effect of a char request.

.rj
.rj n
    Right justify the next n input lines. Without an argument right justify the next input line. The number of lines to be right justifed is available in the \n[.rj] register. This implicitly does .ce 0. The ce request implicitly does .rj 0.

.rnn xx yy
    Rename number register xx to yy.

.shc c
    Set the soft hyphen character to c. If c is omitted, the soft hyphen character will be set to the default \(hy. 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.

.shift n
    In a macro, shift the arguments by n positions: argument i becomes argument i-n; arguments 1 to n will no longer be available. If n is missing, arguments will be shifted by 1. Shifting by negative amounts is currently undefined.

.special s1 s2...
    Fonts s1, s2, are special and will be searched for characters not in the current font.

.sty n f
    Associate style f with font position n. A font position can be associated either with a font or with a style. The current font is the index of a font position and so is also either a font or a style. When it is a style, the font that is actually used is the font the name of which is the concatenation of the name of the current family and the name of the current style. For example, if the current font is 1 and font position 1 is associated with style R and the current font family is T, then font TR will be used. If the current font is not a style, then the current family is ignored. When the requests cs, bd, tkf, uf, or fspecial are applied to a style, then they will instead be applied to the member of the current family corresponding to that style. The default family can be set with the -f option. The styles command in the DESC file controls which font positions (if any) are initially associated with styles rather than fonts.

.tkf f s1 n1 s2 n2
    Enable track kerning for font f. When the current font is f the width of every character will be increased by an amount between n1 and n2: when the current point size is less than or equal to s1 the width will be increased by n1; when it is greater than or equal to s2 the width will be increased by n2; when 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.

.trf filename
    Transparently output the contents of file filename. Each line is output as it would be were it 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, you can define a macro x containing the contents of file f, using

        .di x
        .trf f
        .di

    Unlike with the cf request, the file cannot contain characters such as NUL that are not legal troff input characters.

.troff
    Make the n built-in condition false, and the t built-in condition true. This undoes the effect of the nroff request.

.vpt n
    Enable vertical position traps if n 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.

.warn n
    Control warnings. n 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 in the `Warnings' section. For example, .warn 0 will disable all warnings, and .warn 1 will disable all warnings except that about missing characters. If n is not given, all warnings will be enabled.

.while c anything
    While condition c is true, accept anything as input; c can be any condition acceptable to an if request; anything can comprise multiple lines if the first line starts with \{ and the last line ends with \}. See also the break and continue requests.

.write stream anything
    Write anything to the stream named stream. stream must previously have been the subject of an open request. anything is read in copy mode; a leading " will be stripped.

  Extended requests

.cf filename
    When used in a diversion, this 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.

.ev xx
    If xx is not a number, this will switch to a named environment called xx. The environment should be popped with a matching ev request without any arguments, just as for numbered environments. There is no limit on the number of named environments; they will be created the first time that they are referenced.

.fp n f1 f2
    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 troff after it has been mounted. If there is no third argument then the internal name will be used as the external name. This feature allows you to use fonts with long names in compatibility mode.

.ss m n
    When two arguments are given to the ss request, the second argument gives the sentence space size. If the second argument is not given, the sentence space size will be the same as the word space size. Like the word space size, the sentence space is in units of one twelfth of the spacewidth parameter for the current font. Initially both the word space size and the sentence space size are 12. 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, you should always follow a sentence with either a newline or two spaces.

.ta n1 n2...nn T r1 r2...rn
    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. For example,

        .ta T .5i

    will set tabs every half an inch.

  New number registers
The following read-only registers are available:

\n[.C]
    1 if compatibility mode is in effect, 0 otherwise.

\n[.cdp]
    The depth of the last character added to the current environment. It is positive if the character extends below the baseline.

\n[.ce]
    The number of lines remaining to be centered, as set by the ce request.

\n[.cht]
    The height of the last character added to the current environment. It is positive if the character extends above the baseline.

\n[.csk]
    The skew of the last character added to the current environment. The skew of a character is how far to the right of the center of a character the center of an accent over that character should be placed.

\n[.ev]
    The name or number of the current environment. This is a string-valued register.

\n[.fam]
    The current font family. This is a string-valued register.

\n[.fp]
    The number of the next free font position.

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

\n[.hlc]
    The number of immediately preceding consecutive hyphenated lines.

\n[.hlm]
    The maximum allowed number of consecutive hyphenated lines, as set by the hlm request.

\n[.hy]
    The current hyphenation flags (as set by the hy request.)

\n[.hym]
    The current hyphenation margin (as set by the hym request.)

\n[.hys]
    The current hyphenation space (as set by the hys request.)

\n[.in]
    The indent that applies to the current output line.

\n[.kern]
    1 if pairwise kerning is enabled, 0 otherwise.

\n[.lg]
    The current ligature mode (as set by the lg request.)

\n[.ll]
    The line length that applies to the current output line.

\n[.lt]
    The title length as set by the lt request.

\n[.ne]
    The amount of space that was needed in the last ne request that caused a trap to be sprung. Useful in conjunction with the \n[.trunc] register.

\n[.pn]
    The number of the next page: either the value set by a pn request, or the number of the current page plus 1.

\n[.ps]
    The current pointsize in scaled points.

\n[.psr]
    The last-requested pointsize in scaled points.

\n[.rj]
    The number of lines to be right-justified as set by the rj request.

\n[.sr]
    The last requested pointsize in points as a decimal fraction. This is a string-valued register.

\n[.tabs]
    A string representation of the current tab settings suitable for use as an argument to the ta request.

\n[.trunc]
    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. Useful in conjunction with the \n[.ne] register.

\n[.ss]
\n[.sss]
    These give the values of the parameters set by the first and second arguments of the ss request.

\n[.vpt]
    1 if vertical position traps are enabled, 0 otherwise.

\n[.warn]
    The sum of the numbers associated with each of the currently enabled warnings. The number associated with each warning is listed in the `Warnings' subsection.

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

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

The following registers are set by the \w escape sequence:

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

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

\n[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.

The following read/write number registers are available:

\n[systat]
    The return value of the system() function executed by the last sy request.

\n[slimit]
    If greater than 0, the maximum number of objects on the input stack. If less than or equal to 0, there is no limit on the number of objects on the input stack. With no limit, recursion can continue until virtual memory is exhausted.

  Miscellaneous

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 \n[.fp] register; although troff 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.

Interpolating a string does not hide existing macro arguments. Thus in a macro, a more efficient way of doing

    .xx \\$@

is

    \\*[xx]\\

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 a \& between them.

In a string comparison in a condition, characters that appear at different input levels to the first delimiter character will not be recognised as the second or third delimiters. This applies also to the tl request. In a \w escape sequence, a character that appears at a different input level to the starting delimiter character will not be recognised as the closing delimiter character. When decoding a macro argument that is delimited by double quotes, a character that appears at a different input level to the starting delimiter character will not be recognised as the closing delimiter character. The implementation of \$@ ensures that the double quotes surrounding an argument will appear the same input level, which will be different to the input level of the argument itself. In a long escape name ] will not be recognized as a closing delimiter except when it occurs at the same input level as the opening ]. In compatibility mode, no attention is paid to the input-level.

There are some new types of condition:

.if rxxx
    True if there is a number register named xxx.

.if dxxx
    True if there is a string, macro, diversion, or request named xxx.

.if cch
    True if there is a character ch available; ch is either an ASCII character or a special character \(xx or \[xxx]; the condition will also be true if ch has been defined by the char request.

  Warnings
The warnings that can be given by troff 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.

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.

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.

There are also names that can be used to refer to groups of warnings:

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.

  Incompatibilities

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 recognised. Compatibility mode can be turned on with the -C command line option, and turned on or off with the cp request. The number register \n(.C is 1 if compatibility mode is on, 0 otherwise.

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

Fractional pointsizes cause one noteworthy incompatibility. In Unix troff the ps request ignores scale indicators and so

    .ps 10u

will set the pointsize to 10 points, whereas in GNU troff it will set the pointsize to 10 scaled points.

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 \s is turned into one output \ and the resulting output \s 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 \ 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. If you wish for some reason to store in a diversion an escape sequence that will be interpreted when the diversion is reread, you can either use the traditional \! transparent output facility, or, if this is unsuitable, the new \? escape sequence.

ENVIRONMENT

GROFF_TMAC_PATH
    A colon separated list of directories in which to search for macro files.

GROFF_TYPESETTER
    Default device.

GROFF_FONT_PATH
    A colon separated list of directories in which to search for the devname directory. troff will search in directories given in the -F option before these, and in standard directories (.:/usr/lib/groff/font:/usr/lib/font:/usr/lib/font) after these.

GROFF_HYPHEN
    File containing hyphenation patterns.

FILES
/usr/lib/groff/hyphen Hyphenation patterns

/usr/lib/groff/tmac/troffrc
    Initialization file

/usr/lib/groff/tmac/tmac.name
    Macro files

/usr/lib/groff/font/devname/DESC
    Device description file for device name.

/usr/lib/groff/font/devname/F
    Font file for font F of device name.

SEE ALSO
groff(1) gtbl(1), gpic(1), geqn(1), grops(1), grodvi(1), grotty(1), groff_font(5), groff_out(5), groff_char(7)