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1 .ig \"-*- nroff -*-
2 Copyright (C) 1989-2000 Free Software Foundation, Inc.
4 Permission is granted to make and distribute verbatim copies of
5 this manual provided the copyright notice and this permission notice
6 are preserved on all copies.
8 Permission is granted to copy and distribute modified versions of this
9 manual under the conditions for verbatim copying, provided that the
10 entire resulting derived work is distributed under the terms of a
11 permission notice identical to this one.
13 Permission is granted to copy and distribute translations of this
14 manual into another language, under the above conditions for modified
15 versions, except that this permission notice may be included in
16 translations approved by the Free Software Foundation instead of in
17 the original English.
18 ..
19 .\" define a string tx for the TeX logo
20 .ie t .ds tx T\h'-.1667m'\v'.224m'E\v'-.224m'\h'-.125m'X
21 .el .ds tx TeX
22 .de TQ
23 .br
24 .ns
25 .TP \\$1
26 ..
27 .\" Like TP, but if specified indent is more than half
28 .\" the current line-length - indent, use the default indent.
29 .de Tp
30 .ie \\n(.$=0:((0\\$1)*2u>(\\n(.lu-\\n(.iu)) .TP
31 .el .TP "\\$1"
32 ..
33 .\" The BSD man macros can't handle " in arguments to font change macros,
34 .\" so use \(ts instead of ".
35 .tr \(ts"
36 .TH @G@TROFF @MAN1EXT@ "@MDATE@" "Groff Version @VERSION@"
37 .SH NAME
38 @g@troff \- format documents
39 .SH SYNOPSIS
40 .nr a \n(.j
41 .ad l
42 .nr i \n(.i
43 .in +\w'\fB@g@troff 'u
44 .ti \niu
45 .B @g@troff
46 .de OP
47 .ie \\n(.$-1 .RI "[\ \fB\\$1\fP" "\\$2" "\ ]"
48 .el .RB "[\ " "\\$1" "\ ]"
49 ..
50 .OP \-abivzCERU
51 .OP \-w name
52 .OP \-W name
53 .OP \-d cs
54 .OP \-f fam
55 .OP \-m name
56 .OP \-n num
57 .OP \-o list
58 .OP \-r cn
59 .OP \-T name
60 .OP \-F dir
61 .OP \-M dir
62 .RI "[\ " files\|.\|.\|. "\ ]"
63 .br
64 .ad \na
65 .PP
66 It is possible to have whitespace between a command line option and its
67 parameter.
68 .SH DESCRIPTION
69 This manual page describes the GNU version of
70 .BR troff ,
71 which is part of the groff document formatting system.
72 It is highly compatible with Unix troff.
73 Usually it should be invoked using the groff command, which will
74 also run preprocessors and postprocessors in the appropriate
75 order and with the appropriate options.
76 .SH OPTIONS
77 .TP \w'\-dname=s'u+2n
78 .B \-a
79 Generate an
80 .SM ASCII
81 approximation of the typeset output.
82 .TP
83 .B \-b
84 Print a backtrace with each warning or error message. This backtrace
85 should help track down the cause of the error. The line numbers given
86 in the backtrace may not always be correct:
87 .BR troff 's
88 idea of line numbers
89 gets confused by
90 .B as
91 or
92 .B am
93 requests.
94 .TP
95 .B \-i
96 Read the standard input after all the named input files have been
97 processed.
98 .TP
99 .B \-v
100 Print the version number.
101 .TP
102 .BI \-w name
103 Enable warning
104 .IR name .
105 Available warnings are described in
106 the Warnings subsection below.
107 Multiple
108 .B \-w
109 options are allowed.
110 .TP
111 .BI \-W name
112 Inhibit warning
113 .IR name .
114 Multiple
115 .B \-W
116 options are allowed.
117 .TP
118 .B \-E
119 Inhibit all error messages.
120 .TP
121 .B \-z
122 Suppress formatted output.
123 .TP
124 .B \-C
125 Enable compatibility mode.
126 .TP
127 .BI \-d cs
128 .TQ
129 .BI \-d name = s
130 Define
131 .I c
132 or
133 .I name
134 to be a string
135 .IR s ;
136 .I c
137 must be a one letter name.
138 .TP
139 .BI \-f fam
140 Use
141 .I fam
142 as the default font family.
143 .TP
144 .BI \-m name
145 Read in the file
146 .BI tmac. name\fR.
147 Normally this will be searched for in @MACRODIR@.
148 By default, the
149 .I safer
150 macro is used (this can be reverted using
151 .BR \-U ).
152 .TP
153 .B \-U
154 Unsafe option, avoids default use of
155 .I safer
156 macro.
157 .TP
158 .B \-R
159 Don't load
160 .B troffrc
161 and
162 .BR troffrc-end .
163 .TP
164 .BI \-n num
165 Number the first page
166 .IR num .
167 .TP
168 .BI \-o list
169 Output only pages in
170 .IR list ,
171 which is a comma-separated list of page ranges;
172 .I n
173 means print page
174 .IR n ,
175 .IB m \- n
176 means print every page between
177 .I m
178 and
179 .IR n ,
180 .BI \- n
181 means print every page up to
182 .IR n ,
183 .IB n \-
184 means print every page from
185 .IR n .
186 .B Troff
187 will exit after printing the last page in the list.
188 .TP
189 .BI \-r cn
190 .TQ
191 .BI \-r name = n
192 Set number register
193 .I c
194 or
195 .I name
196 to
197 .IR n ;
198 .I c
199 must be a one character name;
200 .I n
201 can be any troff numeric expression.
202 .TP
203 .BI \-T name
204 Prepare output for device
205 .IR name ,
206 rather than the default
207 .BR @DEVICE@ .
208 .TP
209 .BI \-F dir
210 Search
211 .I dir
212 for subdirectories
213 .BI dev name
214 .RI ( name
215 is the name of the device)
216 for the
217 .B DESC
218 file and font files before the normal
219 .BR @FONTDIR@ .
220 .TP
221 .BI \-M dir
222 Search directory
223 .I dir
224 for macro files before the normal
225 .BR @MACRODIR@ .
226 .SH USAGE
227 Only the features not in Unix troff are described here.
228 .SS Long names
229 The names of number registers, fonts, strings/macros/diversions,
230 special characters can be of any length. In escape sequences, where
231 you can use
232 .BI ( xx
233 for a two character name, you can use
234 .BI [ xxx ]
235 for a name of arbitrary length:
236 .TP
237 .BI \e[ xxx ]
238 Print the special character called
239 .IR xxx .
240 .TP
241 .BI \ef[ xxx ]
242 Set font
243 .IR xxx .
244 .TP
245 .BI \e*[ xxx ]
246 Interpolate string
247 .IR xxx .
248 .TP
249 .BI \en[ xxx ]
250 Interpolate number register
251 .IR xxx .
252 .SS Fractional pointsizes
253 A
254 .I
255 scaled point
256 is equal to 1/sizescale
257 points, where
258 sizescale is specified in the
259 .B DESC
260 file (1 by default.)
261 There is a new scale indicator
262 .B z
263 which has the effect of multiplying by sizescale.
264 Requests and escape sequences in troff
265 interpret arguments that represent a pointsize as being in units
266 of scaled points, but they evaluate each such argument
267 using a default scale indicator of
268 .BR z .
269 Arguments treated in this way are
270 the argument to the
271 .B ps
272 request,
273 the third argument to the
274 .B cs
275 request,
276 the second and fourth arguments to the
277 .B tkf
278 request,
279 the argument to the
280 .B \eH
281 escape sequence,
282 and those variants of the
283 .B \es
284 escape sequence that take a numeric expression as their argument.
285 .LP
286 For example, suppose sizescale is 1000;
287 then a scaled point will be equivalent to a millipoint;
288 the request
289 .B .ps 10.25
290 is equivalent to
291 .B .ps 10.25z
292 and so sets the pointsize to 10250 scaled points,
293 which is equal to 10.25 points.
294 .LP
295 The number register
296 .B \en(.s
297 returns the pointsize in points as decimal fraction.
298 There is also a new number register
299 .B \en[.ps]
300 that returns the pointsize in scaled points.
301 .LP
302 It would make no sense to use the
303 .B z
304 scale indicator in a numeric expression
305 whose default scale indicator was neither
306 .B u
307 nor
308 .BR z ,
309 and so
310 .B troff
311 disallows this.
312 Similarly it would make no sense to use a scaling indicator
313 other than
314 .B z
315 or
316 .B u
317 in a numeric expression whose default scale indicator was
318 .BR z ,
319 and so
320 .B troff
321 disallows this as well.
322 .LP
323 There is also new scale indicator
324 .B s
325 which multiplies by the number of units in a scaled point.
326 So, for example,
327 .B \en[.ps]s
328 is equal to
329 .BR 1m .
330 Be sure not to confuse the
331 .B s
332 and
333 .B z
334 scale indicators.
335 .SS Numeric expressions
336 .LP
337 Spaces are permitted in a number expression within parentheses.
338 .LP
339 .B M
340 indicates a scale of 100ths of an em.
341 .TP
342 .IB e1 >? e2
343 The maximum of
344 .I e1
345 and
346 .IR e2 .
347 .TP
348 .IB e1 <? e2
349 The minimum of
350 .I e1
351 and
352 .IR e2 .
353 .TP
354 .BI ( c ; e )
355 Evaluate
356 .I e
357 using
358 .I c
359 as the default scaling indicator.
360 If
361 .I c
362 is missing, ignore scaling indicators in the evaluation of
363 .IR e .
364 .SS New escape sequences
365 .TP
366 .BI \eA' anything '
367 This expands to
368 .B 1
369 or
370 .B 0
371 according as
372 .I anything
373 is or is not acceptable as the name of a string, macro, diversion,
374 number register, environment or font.
375 It will return
376 .B 0
377 if
378 .I anything
379 is empty.
380 This is useful if you want to lookup user input in some sort of
381 associative table.
382 .TP
383 .BI \eC' xxx '
384 Typeset character named
385 .IR xxx .
386 Normally it is more convenient to use
387 .BI \e[ xxx ]\fR.
388 But
389 .B \eC
390 has the advantage that it is compatible with recent versions of
391 .SM UNIX
392 and is available in compatibility mode.
393 .TP
394 .B \eE
395 This is equivalent to an escape character,
396 but it's not interpreted in copy-mode.
397 For example, strings to start and end superscripting could be defined
398 like this:
399 .RS
400 .IP
401 \&.ds { \ev'\-.3m'\es'\eEn[.s]*6u/10u'
402 .br
403 \&.ds } \es0\ev'.3m'
404 .LP
405 The use of
406 .B \eE
407 ensures that these definitions will work even if
408 .B \e*{
409 gets interpreted in copy-mode
410 (for example, by being used in a macro argument.)
411 .RE
412 .TP
413 .BI \eN' n '
414 Typeset the character with code
415 .I n
416 in the current font.
417 .I n
418 can be any integer.
419 Most devices only have characters with codes between 0 and 255.
420 If the current font does not contain a character with that code,
421 special fonts will
422 .I not
423 be searched.
424 The
425 .B \eN
426 escape sequence can be conveniently used on conjunction with the
427 .B char
428 request:
429 .RS
430 .IP
431 .B
432 \&.char \e[phone] \ef(ZD\eN'37'
433 .RE
434 .IP
435 The code of each character is given in the fourth column in the font
436 description file after the
437 .B charset
438 command.
439 It is possible to include unnamed characters in the font description
440 file by using a name of
441 .BR \-\-\- ;
442 the
443 .B \eN
444 escape sequence is the only way to use these.
445 .TP
446 .BI \eR' name\ \(+-n '
447 This has the same effect as
448 .RS
449 .IP
450 .BI .nr\ name\ \(+-n
451 .RE
452 .TP
453 .BI \es( nn
454 .TQ
455 .BI \es\(+-( nn
456 Set the point size to
457 .I nn
458 points;
459 .I nn
460 must be exactly two digits.
461 .TP
462 .BI \es[\(+- n ]
463 .TQ
464 .BI \es\(+-[ n ]
465 .TQ
466 .BI \es'\(+- n '
467 .TQ
468 .BI \es\(+-' n '
469 Set the point size to
470 .I n
471 scaled points;
472 .I n
473 is a numeric expression with a default scale indicator of
474 .BR z .
475 .TP
476 .BI \eV x
477 .TQ
478 .BI \eV( xx
479 .TQ
480 .BI \eV[ xxx ]
481 Interpolate the contents of the environment variable
482 .IR xxx ,
483 as returned by
484 .BR getenv (3).
485 .B \eV
486 is interpreted in copy-mode.
487 .TP
488 .BI \eY x
489 .TQ
490 .BI \eY( xx
491 .TQ
492 .BI \eY[ xxx ]
493 This is approximately equivalent to
494 .BI \eX'\e*[ xxx ]'\fR.
495 However the contents of the string or macro
496 .I xxx
497 are not interpreted;
498 also it is permitted for
499 .I xxx
500 to have been defined as a macro and thus contain newlines
501 (it is not permitted for the argument to
502 .B \eX
503 to contain newlines).
504 The inclusion of newlines requires an extension to the Unix troff output
505 format, and will confuse drivers that do not know about this
506 extension.
507 .TP
508 .BI \eZ' anything '
509 Print anything and then restore the horizontal and vertical
510 position;
511 .I anything
512 may not contain tabs or leaders.
513 .TP
514 .B \e$0
515 The name by which the current macro was invoked.
516 The
517 .B als
518 request can make a macro have more than one name.
519 .TP
520 .B \e$*
521 In a macro, the concatenation of all the arguments separated by spaces.
522 .TP
523 .B \e$@
524 In a macro, the concatenation of all the arguments with each surrounded by
525 double quotes, and separated by spaces.
526 .TP
527 .BI \e$( nn
528 .TQ
529 .BI \e$[ nnn ]
530 In a macro, this gives the
531 .IR nn -th
532 or
533 .IR nnn -th
534 argument.
535 Macros can have a unlimited number of arguments.
536 .TP
537 .BI \e? anything \e?
538 When used in a diversion, this will transparently embed
539 .I anything
540 in the diversion.
541 .I anything
542 is read in copy mode.
543 When the diversion is reread,
544 .I anything
545 will be interpreted.
546 .I anything
547 may not contain newlines; use
548 .B \e!
549 if you want to embed newlines in a diversion.
550 The escape sequence
551 .B \e?
552 is also recognised in copy mode and turned into a single internal
553 code; it is this code that terminates
554 .IR anything .
555 Thus
556 .RS
557 .RS
558 .ft B
559 .nf
560 .ne 15
561 \&.nr x 1
562 \&.nf
563 \&.di d
564 \e?\e\e?\e\e\e\e?\e\e\e\e\e\e\e\enx\e\e\e\e?\e\e?\e?
565 \&.di
566 \&.nr x 2
567 \&.di e
568 \&.d
569 \&.di
570 \&.nr x 3
571 \&.di f
572 \&.e
573 \&.di
574 \&.nr x 4
575 \&.f
576 .fi
577 .ft
578 .RE
579 .RE
580 .IP
581 will print
582 .BR 4 .
583 .TP
584 .B \e/
585 This increases the width of the preceding character so that
586 the spacing between that character and the following character
587 will be correct if the following character is a roman character.
588 For example, if an italic f is immediately followed by a roman
589 right parenthesis, then in many fonts the top right portion of the f
590 will overlap the top left of the right parenthesis producing \fIf\fR)\fR,
591 which is ugly.
592 Inserting
593 .B \e/
594 produces
595 .ie \n(.g \fIf\/\fR)\fR
596 .el \fIf\|\fR)\fR
597 and avoids this problem.
598 It is a good idea to use this escape sequence whenever an
599 italic character is immediately followed by a roman character without any
600 intervening space.
601 .TP
602 .B \e,
603 This modifies the spacing of the following character so that the spacing
604 between that character and the preceding character will correct if
605 the preceding character is a roman character.
606 For example, inserting
607 .B \e,
608 between the parenthesis and the f changes
609 \fR(\fIf\fR to
610 .ie \n(.g \fR(\,\fIf\fR.
611 .el \fR(\^\fIf\fR.
612 It is a good idea to use this escape sequence whenever a
613 roman character is immediately followed by an italic character without any
614 intervening space.
615 .TP
616 .B \e)
617 Like
618 .B \e&
619 except that it behaves like a character declared with the
620 .B cflags
621 request to be transparent for the purposes of end of sentence recognition.
622 .TP
623 .B \e~
624 This produces an unbreakable space that stretches like a normal inter-word
625 space when a line is adjusted.
626 .TP
627 .B \e#
628 Everything up to and including the next newline is ignored.
629 This is interpreted in copy mode.
630 This is like
631 .B \e"
632 except that
633 .B \e"
634 does not ignore the terminating newline.
635 .SS New requests
636 .TP
637 .BI .aln\ xx\ yy
638 Create an alias
639 .I xx
640 for number register object named
641 .IR yy .
642 The new name and the old name will be exactly equivalent.
643 If
644 .I yy
645 is undefined, a warning of type
646 .B reg
647 will be generated, and the request will be ignored.
648 .TP
649 .BI .als\ xx\ yy
650 Create an alias
651 .I xx
652 for request, string, macro, or diversion object named
653 .IR yy .
654 The new name and the old name will be exactly equivalent (it is similar to a
655 hard rather than a soft link).
656 If
657 .I yy
658 is undefined, a warning of type
659 .B mac
660 will be generated, and the request will be ignored.
661 The
662 .BR de ,
663 .BR am ,
664 .BR di ,
665 .BR da ,
666 .BR ds ,
667 and
668 .B as
669 requests only create a new object if the name of the macro, diversion
670 or string diversion is currently undefined or if it is defined to be a
671 request; normally they modify the value of an existing object.
672 .TP
673 .BI .asciify\ xx
674 This request only exists in order to make it possible
675 to make certain gross hacks work with GNU troff.
676 It `unformats' the diversion
677 .I xx
678 in such a way that
679 .SM ASCII
680 characters that were formatted and diverted into
681 .I xx
682 will be treated like ordinary input characters when
683 .I xx
684 is reread.
685 For example, this
686 .RS
687 .IP
688 .ne 7v+\n(.Vu
689 .ft B
690 .nf
691 .ss 24
692 \&.tr @.
693 \&.di x
694 \&@nr\e n\e 1
695 \&.br
696 \&.di
697 \&.tr @@
698 \&.asciify x
699 \&.x
700 .ss 12
701 .fi
702 .RE
703 .IP
704 will set register
705 .B n
706 to 1.
707 .TP
708 .B .backtrace
709 Print a backtrace of the input stack on stderr.
710 .TP
711 .BI .blm\ xx
712 Set the blank line macro to
713 .IR xx .
714 If there is a blank line macro,
715 it will be invoked when a blank line is encountered instead of the usual
716 troff behaviour.
717 .TP
718 .B .break
719 Break out of a while loop.
720 See also the
721 .B while
722 and
723 .B continue
724 requests.
725 Be sure not to confuse this with the
726 .B br
727 request.
728 .TP
729 .BI .cflags\ n\ c1\ c2\|.\|.\|.
730 Characters
731 .IR c1 ,
732 .IR c2 ,\|.\|.\|.
733 have properties determined by
734 .IR n ,
735 which is ORed from the following:
736 .RS
737 .TP
738 1
739 the character ends sentences
740 (initially characters
741 .B .?!
742 have this property);
743 .TP
744 2
745 lines can be broken before the character
746 (initially no characters have this property);
747 a line will not be broken at a character with this property
748 unless the characters on each side both have non-zero
749 hyphenation codes.
750 .TP
751 4
752 lines can be broken after the character
753 (initially characters
754 .B \-\e(hy\e(em
755 have this property);
756 a line will not be broken at a character with this property
757 unless the characters on each side both have non-zero
758 hyphenation codes.
759 .TP
760 8
761 the character overlaps horizontally
762 (initially characters
763 .B \e(ul\e(rn\e(ru
764 have this property);
765 .TP
766 16
767 the character overlaps vertically
768 (initially character
769 .B \e(br
770 has this property);
771 .TP
772 32
773 an end of sentence character followed by any number of characters
774 with this property will be treated
775 as the end of a sentence if followed by a newline or two spaces;
776 in other words
777 the character is transparent for the purposes of end of sentence
778 recognition;
779 this is the same as having a zero space factor in \*(tx
780 (initially characters
781 .B \(ts')]*\e(dg\e(rq
782 have this property).
783 .RE
784 .TP
785 .BI .char\ c\ string
786 Define character
787 .I c
788 to be
789 .IR string .
790 Every time character
791 .I c
792 needs to be printed,
793 .I string
794 will be processed in a temporary environment and the result
795 will be wrapped up into a single object.
796 Compatibility mode will be turned off
797 and the escape character will be set to
798 .B \e
799 while
800 .I string
801 is being processed.
802 Any emboldening, constant spacing or track kerning will be applied
803 to this object rather than to individual characters in
804 .IR string .
805 A character defined by this request can be used just like
806 a normal character provided by the output device.
807 In particular other characters can be translated to it
808 with the
809 .B tr
810 request;
811 it can be made the leader character by the
812 .B lc
813 request;
814 repeated patterns can be drawn with the character using the
815 .B \el
816 and
817 .B \eL
818 escape sequences;
819 words containing the character can be hyphenated
820 correctly, if the
821 .B hcode
822 request is used to give the character a hyphenation code.
823 There is a special anti-recursion feature:
824 use of character within the character's definition
825 will be handled like normal characters not defined with
826 .BR char .
827 A character definition can be removed with the
828 .B rchar
829 request.
830 .TP
831 .BI .chop\ xx
832 Chop the last character off macro, string, or diversion
833 .IR xx .
834 This is useful for removing the newline from the end of diversions
835 that are to be interpolated as strings.
836 .TP
837 .BI .close\ stream
838 Close the stream named
839 .IR stream ;
840 .I stream
841 will no longer be an acceptable argument to the
842 .B write
843 request.
844 See the
845 .B open
846 request.
847 .TP
848 .B .continue
849 Finish the current iteration of a while loop.
850 See also the
851 .B while
852 and
853 .B break
854 requests.
855 .TP
856 .BI .cp\ n
857 If
858 .I n
859 is non-zero or missing, enable compatibility mode, otherwise
860 disable it.
861 In compatibility mode, long names are not recognised, and the
862 incompatibilities caused by long names do not arise.
863 .TP
864 .BI .do\ xxx
865 Interpret
866 .I .xxx
867 with compatibility mode disabled.
868 For example,
869 .RS
870 .IP
871 .B
872 \&.do fam T
873 .LP
874 would have the same effect as
875 .IP
876 .B
877 \&.fam T
878 .LP
879 except that it would work even if compatibility mode had been enabled.
880 Note that the previous compatibility mode is restored before any files
881 sourced by
882 .I xxx
883 are interpreted.
884 .RE
885 .TP
886 .BI .evc\ xx
887 Copy the contents of environment
888 .I xx
889 to the current environment.
890 No pushing or popping of environents will be done.
891 .TP
892 .BI .fam\ xx
893 Set the current font family to
894 .IR xx .
895 The current font family is part of the current environment.
896 See the description of the
897 .B sty
898 request for more information on font families.
899 .TP
900 .BI .fspecial\ f\ s1\ s2\|.\|.\|.
901 When the current font is
902 .IR f ,
903 fonts
904 .IR s1 ,
905 .IR s2 ,\|.\|.\|.
906 will be special, that is, they will searched for characters not in
907 the current font.
908 Any fonts specified in the
909 .B special
910 request will be searched after fonts specified in the
911 .B fspecial
912 request.
913 .TP
914 .BI .ftr\ f\ g
915 Translate font
916 .I f
917 to
918 .IR g .
919 Whenever a font named
920 .I f
921 is referred to in
922 .B \ef
923 escape sequence,
924 or in the
925 .BR ft ,
926 .BR ul ,
927 .BR bd ,
928 .BR cs ,
929 .BR tkf ,
930 .BR special ,
931 .BR fspecial ,
932 .BR fp ,
933 or
934 .BR sty
935 requests,
936 font
937 .I g
938 will be used.
939 If
940 .I g
941 is missing,
942 or equal to
943 .I f
944 then font
945 .I f
946 will not be translated.
947 .TP
948 .BI .hcode \ c1\ code1\ c2\ code2\|.\|.\|.
949 Set the hyphenation code of character
950 .I c1
951 to
952 .I code1
953 and that of
954 .I c2
955 to
956 .IR code2 .
957 A hyphenation code must be a single input
958 character (not a special character) other than a digit or a space.
959 Initially each lower-case letter has a hyphenation code, which
960 is itself, and each upper-case letter has a hyphenation code
961 which is the lower case version of itself.
962 See also the
963 .B hpf
964 request.
965 .TP
966 .BI .hla\ lang
967 Set the current hyphenation language to
968 .IR lang .
969 Hyphenation exceptions specified with the
970 .B hw
971 request and hyphenation patterns specified with the
972 .B hpf
973 request are both associated with the current hyphenation language.
974 The
975 .B hla
976 request is usually invoked by the
977 .B troffrc
978 file.
979 .TP
980 .BI .hlm\ n
981 Set the maximum number of consecutive hyphenated lines to
982 .IR n .
983 If
984 .I n
985 is negative, there is no maximum.
986 The default value is \-1.
987 This value is associated with the current environment.
988 Only lines output from an environment count towards the maximum associated
989 with that environment.
990 Hyphens resulting from
991 .B \e%
992 are counted; explicit hyphens are not.
993 .TP
994 .BI .hpf\ file
995 Read hyphenation patterns from
996 .IR file ;
997 this will be searched for in the same way that
998 .BI tmac. name
999 is searched for when the
1000 .BI \-m name
1001 option is specified.
1002 It should have the same format as the argument to
1003 the \epatterns primitive in \*(tx;
1004 the letters appearing in this file are interpreted as hyphenation
1005 codes.
1006 A
1007 .B %
1008 character in the patterns file introduces a comment that continues
1009 to the end of the line.
1010 The set of hyphenation patterns is associated with the current language
1011 set by the
1012 .B hla
1013 request.
1014 The
1015 .B hpf
1016 request
1017 is usually invoked by the
1018 .B troffrc
1019 file.
1020 .TP
1021 .BI .hym\ n
1022 Set the
1023 .I hyphenation margin
1024 to
1025 .IR n :
1026 when the current adjustment mode is not
1027 .BR b ,
1028 the line will not be hyphenated if the line is no more than
1029 .I n
1030 short.
1031 The default hyphenation margin is 0.
1032 The default scaling indicator for this request is
1033 .IR m .
1034 The hyphenation margin is associated with the current environment.
1035 The current hyphenation margin is available in the
1036 .B \en[.hym]
1037 register.
1038 .TP
1039 .BI .hys\ n
1040 Set the
1041 .I hyphenation space
1042 to
1043 .IR n :
1044 when the current adjustment mode is
1045 .B b
1046 don't hyphenate the line if the line can be justified by adding no more than
1047 .I n
1048 extra space to each word space.
1049 The default hyphenation space is 0.
1050 The default scaling indicator for this request is
1051 .BR m .
1052 The hyphenation space is associated with the current environment.
1053 The current hyphenation space is available in the
1054 .B \en[.hys]
1055 register.
1056 .TP
1057 .BI .kern\ n
1058 If
1059 .I n
1060 is non-zero or missing, enable pairwise kerning, otherwise disable it.
1061 .TP
1062 .BI .length\ xx\ string
1063 Compute the length of
1064 .I string
1065 and return it in the number register
1066 .I xx
1067 (which is not necessarily defined before).
1068 .TP
1069 .BI .mso\ file
1070 The same as the
1071 .B so
1072 request except that
1073 .I file
1074 is searched for in the same directories as
1075 .BI tmac. name
1076 is searched for when the
1077 .BI \-m name
1078 option is specified.
1079 .TP
1080 .B .nroff
1081 Make the
1082 .B n
1083 built-in condition true
1084 and the
1085 .B t
1086 built-in condition false.
1087 This can be reversed using the
1088 .B troff
1089 request.
1090 .TP
1091 .BI .open\ stream\ filename
1092 Open
1093 .I filename
1094 for writing and associate the stream named
1095 .I stream
1096 with it.
1097 See also the
1098 .B close
1099 and
1100 .B write
1101 requests.
1102 .TP
1103 .BI .opena\ stream\ filename
1104 Like
1105 .BR open ,
1106 but if
1107 .I filename
1108 exists, append to it instead of truncating it.
1109 .TP
1110 .B .pnr
1111 Print the names and contents of all currently defined number registers
1112 on stderr.
1113 .TP
1114 .BI .psbb \ filename
1115 Get the bounding box of a PostScript image
1116 .IR filename .
1117 This file must conform to Adobe's Document Structuring Conventions; the
1118 command looks for a
1119 .B %%BoundingBox
1120 comment to extract the bounding box values.
1121 After a successful call, the coordinates (in PostScript units) of the lower
1122 left and upper right corner can be found in the registers
1123 .BR \en[llx] ,
1124 .BR \en[lly] ,
1125 .BR \en[urx] ,
1126 and
1127 .BR \en[ury] ,
1128 respectively.
1129 If some error has occurred, the four registers are set to zero.
1130 .TP
1131 .BI .pso \ command
1132 This behaves like the
1133 .B so
1134 request except that input comes from the standard output of
1135 .IR command .
1136 .TP
1137 .B .ptr
1138 Print the names and positions of all traps (not including input line
1139 traps and diversion traps) on stderr. Empty slots in the page trap
1140 list are printed as well, because they can affect the priority of
1141 subsequently planted traps.
1142 .TP
1143 .BI .rchar\ c1\ c2\|.\|.\|.
1144 Remove the definitions of characters
1145 .IR c1 ,
1146 .IR c2 ,\|.\|.\|.
1147 This undoes the effect of a
1148 .B char
1149 request.
1150 .TP
1151 .B .rj
1152 .TQ
1153 .BI .rj\ n
1154 Right justify the next
1155 .I n
1156 input lines.
1157 Without an argument right justify the next input line.
1158 The number of lines to be right justified is available in the
1159 .B \en[.rj]
1160 register.
1161 This implicitly does
1162 .BR .ce\ 0 .
1163 The
1164 .B ce
1165 request implicitly does
1166 .BR .rj\ 0 .
1167 .TP
1168 .BI .rnn \ xx\ yy
1169 Rename number register
1170 .I xx
1171 to
1172 .IR yy .
1173 .TP
1174 .BI .shc\ c
1175 Set the soft hyphen character to
1176 .IR c .
1177 If
1178 .I c
1179 is omitted,
1180 the soft hyphen character will be set to the default
1181 .BR \e(hy .
1182 The soft hyphen character is the character which will be inserted
1183 when a word is hyphenated at a line break.
1184 If the soft hyphen character does not exist in the font of the character
1185 immediately preceding a potential break point,
1186 then the line will not be broken at that point.
1187 Neither definitions (specified with the
1188 .B char
1189 request)
1190 nor translations (specified with the
1191 .B tr
1192 request)
1193 are considered when finding the soft hyphen character.
1194 .TP
1195 .BI .shift\ n
1196 In a macro, shift the arguments by
1197 .I n
1198 positions:
1199 argument
1200 .I i
1201 becomes argument
1202 .IR i \- n ;
1203 arguments 1 to
1204 .I n
1205 will no longer be available.
1206 If
1207 .I n
1208 is missing,
1209 arguments will be shifted by 1.
1210 Shifting by negative amounts is currently undefined.
1211 .TP
1212 .BI .special\ s1\ s2\|.\|.\|.
1213 Fonts
1214 .IR s1 ,
1215 .IR s2 ,
1216 are special and will be searched for characters not in the
1217 current font.
1218 .TP
1219 .BI .sty\ n\ f
1220 Associate style
1221 .I f
1222 with font position
1223 .IR n .
1224 A font position can be associated either with a font or
1225 with a style.
1226 The current font is the index of a font position and so is also
1227 either a font or a style.
1228 When it is a style, the font that is actually used is the font the
1229 name of which is the concatenation of the name of the current family
1230 and the name of the current style.
1231 For example, if the current font is 1 and font position 1 is
1232 associated with style
1233 .B R
1234 and the current
1235 font family is
1236 .BR T ,
1237 then font
1238 .BR TR
1239 will be used.
1240 If the current font is not a style, then the current family is ignored.
1241 When the requests
1242 .BR cs ,
1243 .BR bd ,
1244 .BR tkf ,
1245 .BR uf ,
1246 or
1247 .B fspecial
1248 are applied to a style,
1249 then they will instead be applied to the member of the
1250 current family corresponding to that style.
1251 The default family can be set with the
1252 .B \-f
1253 option.
1254 The styles command in the
1255 .SM DESC
1256 file controls which font positions
1257 (if any) are initially associated with styles rather than fonts.
1258 .TP
1259 .BI .substring\ xx\ n1\ [ n2 ]
1260 Replace the string in register
1261 .I xx
1262 with the substring defined by the indices
1263 .I n1
1264 and
1265 .IR n2 .
1266 The first character in the string has index one.
1267 If
1268 .I n2
1269 is omitted, it is taken to be equal to the string's length. If the
1270 index value
1271 .I n1
1272 or
1273 .I n2
1274 is negative or zero, it will be counted from the end of the string,
1275 going backwards: The last character has index 0, the character before
1276 the last character has index -1, etc.
1277 .TP
1278 .BI .tkf\ f\ s1\ n1\ s2\ n2
1279 Enable track kerning for font
1280 .IR f .
1281 When the current font is
1282 .I f
1283 the width of every character will be increased by an amount
1284 between
1285 .I n1
1286 and
1287 .IR n2 ;
1288 when the current point size is less than or equal to
1289 .I s1
1290 the width will be increased by
1291 .IR n1 ;
1292 when it is greater than or equal to
1293 .I s2
1294 the width will be increased by
1295 .IR n2 ;
1296 when the point size is greater than or equal to
1297 .I s1
1298 and less than or equal to
1299 .I s2
1300 the increase in width is a linear function of the point size.
1301 .TP
1302 .BI .trf\ filename
1303 Transparently output the contents of file
1304 .IR filename .
1305 Each line is output as it would be were it preceded by
1306 .BR \e! ;
1307 however, the lines are not subject to copy-mode interpretation.
1308 If the file does not end with a newline, then a newline will
1309 be added.
1310 For example, you can define a macro
1311 .I x
1312 containing the contents of file
1313 .IR f ,
1314 using
1315 .RS
1316 .IP
1317 .BI .di\ x
1318 .br
1319 .BI .trf\ f
1320 .br
1321 .B .di
1322 .LP
1323 Unlike with the
1324 .B cf
1325 request,
1326 the file cannot contain characters such as
1327 .SM NUL
1328 that are not legal troff input characters.
1329 .RE
1330 .TP
1331 .B .trnt abcd
1332 This is the same as the
1333 .B tr
1334 request except that the translations do not apply to text that is
1335 transparently throughput into a diversion with
1336 .BR \e! .
1337 For example,
1338 .RS
1339 .LP
1340 .nf
1341 .ft B
1342 \&.tr ab
1343 \&.di x
1344 \e!.tm a
1345 \&.di
1346 \&.x
1347 .fi
1348 .ft
1349 .LP
1350 will print
1351 .BR b ;
1352 if
1353 .B trnt
1354 is used instead of
1355 .B tr
1356 it will print
1357 .BR a .
1358 .RE
1359 .TP
1360 .B .troff
1361 Make the
1362 .B n
1363 built-in condition false,
1364 and the
1365 .B t
1366 built-in condition true.
1367 This undoes the effect of the
1368 .B nroff
1369 request.
1370 .TP
1371 .BI .vpt\ n
1372 Enable vertical position traps if
1373 .I n
1374 is non-zero, disable them otherwise.
1375 Vertical position traps are traps set by the
1376 .B wh
1377 or
1378 .B dt
1379 requests.
1380 Traps set by the
1381 .B it
1382 request are not vertical position traps.
1383 The parameter that controls whether vertical position traps are enabled
1384 is global.
1385 Initially vertical position traps are enabled.
1386 .TP
1387 .BI .warn\ n
1388 Control warnings.
1389 .I n
1390 is the sum of the numbers associated with each warning that is to be enabled;
1391 all other warnings will be disabled.
1392 The number associated with each warning is listed in the `Warnings' section.
1393 For example,
1394 .B .warn 0
1395 will disable all warnings, and
1396 .B .warn 1
1397 will disable all warnings except that about missing characters.
1398 If
1399 .I n
1400 is not given,
1401 all warnings will be enabled.
1402 .TP
1403 .BI .while \ c\ anything
1404 While condition
1405 .I c
1406 is true, accept
1407 .I anything
1408 as input;
1409 .I c
1410 can be any condition acceptable to an
1411 .B if
1412 request;
1413 .I anything
1414 can comprise multiple lines if the first line starts with
1415 .B \e{
1416 and the last line ends with
1417 .BR \e} .
1418 See also the
1419 .B break
1420 and
1421 .B continue
1422 requests.
1423 .TP
1424 .BI .write\ stream\ anything
1425 Write
1426 .I anything
1427 to the stream named
1428 .IR stream .
1429 .I stream
1430 must previously have been the subject of an
1431 .B open
1432 request.
1433 .I anything
1434 is read in copy mode;
1435 a leading
1436 .B \(ts
1437 will be stripped.
1438 .SS Extended requests
1439 .TP
1440 .BI .cf\ filename
1441 When used in a diversion, this will embed in the diversion an object which,
1442 when reread, will cause the contents of
1443 .I filename
1444 to be transparently copied through to the output.
1445 In Unix troff, the
1446 contents of
1447 .I filename
1448 is immediately copied through to the output regardless of whether
1449 there is a current diversion; this behaviour is so anomalous that it
1450 must be considered a bug.
1451 .TP
1452 .BI .ev\ xx
1453 If
1454 .I xx
1455 is not a number, this will switch to a named environment called
1456 .IR xx .
1457 The environment should be popped with a matching
1458 .B ev
1459 request without any arguments, just as for numbered environments.
1460 There is no limit on the number of named environments; they will be
1461 created the first time that they are referenced.
1462 .TP
1463 .BI .fp\ n\ f1\ f2
1464 The
1465 .B fp
1466 request has an optional third argument.
1467 This argument gives the external name of the font,
1468 which is used for finding the font description file.
1469 The second argument gives the internal name of the font
1470 which is used to refer to the font in troff after it has been mounted.
1471 If there is no third argument then the internal name will be used
1472 as the external name.
1473 This feature allows you to use fonts with long names in compatibility mode.
1474 .TP
1475 .BI .ss\ m\ n
1476 When two arguments are given to the
1477 .B ss
1478 request, the second argument gives the
1479 .IR "sentence space size" .
1480 If the second argument is not given, the sentence space size
1481 will be the same as the word space size.
1482 Like the word space size, the sentence space is in units of
1483 one twelfth of the spacewidth parameter for the current font.
1484 Initially both the word space size and the sentence
1485 space size are 12.
1486 The sentence space size is used in two circumstances:
1487 if the end of a sentence occurs at the end of a line in fill mode, then
1488 both an inter-word space and a sentence space will be added;
1489 if two spaces follow the end of a sentence in the middle of a line,
1490 then the second space will be a sentence space.
1491 Note that the behaviour of Unix troff will be exactly
1492 that exhibited by GNU troff if a second argument is never given to the
1493 .B ss
1494 request.
1495 In GNU troff, as in Unix troff, you should always
1496 follow a sentence with either a newline or two spaces.
1497 .TP
1498 .BI .ta\ n1\ n2\|.\|.\|.nn \ T\ r1\ r2\|.\|.\|.\|rn
1499 Set tabs at positions
1500 .IR n1 ,
1501 .IR n2 ,\|.\|.\|.\|,
1502 .I nn
1503 and then set tabs at
1504 .IR nn + r1 ,
1505 .IR nn + r2 ,\|.\|.\|.\|.\|,
1506 .IR nn + rn
1507 and then at
1508 .IR nn + rn + r1 ,
1509 .IR nn + rn + r2 ,\|.\|.\|.\|,
1510 .IR nn + rn + rn ,
1511 and so on.
1512 For example,
1513 .RS
1514 .IP
1515 .B
1516 \&.ta T .5i
1517 .LP
1518 will set tabs every half an inch.
1519 .RE
1520 .SS New number registers
1521 The following read-only registers are available:
1522 .TP
1523 .B \en[.C]
1524 1 if compatibility mode is in effect, 0 otherwise.
1525 .TP
1526 .B \en[.cdp]
1527 The depth of the last character added to the current environment.
1528 It is positive if the character extends below the baseline.
1529 .TP
1530 .B \en[.ce]
1531 The number of lines remaining to be centered, as set by the
1532 .B ce
1533 request.
1534 .TP
1535 .B \en[.cht]
1536 The height of the last character added to the current environment.
1537 It is positive if the character extends above the baseline.
1538 .TP
1539 .B \en[.csk]
1540 The skew of the last character added to the current environment.
1541 The
1542 .I skew
1543 of a character is how far to the right of the center of a character
1544 the center of an accent over that character should be placed.
1545 .TP
1546 .B \en[.ev]
1547 The name or number of the current environment.
1548 This is a string-valued register.
1549 .TP
1550 .B \en[.fam]
1551 The current font family.
1552 This is a string-valued register.
1553 .TP
1554 .B \en[.fp]
1555 The number of the next free font position.
1556 .TP
1557 .B \en[.g]
1558 Always 1.
1559 Macros should use this to determine whether they are running
1560 under GNU troff.
1561 .TP
1562 .B \en[.hla]
1563 The current hyphenation language as set by the
1564 .B hla
1565 request.
1566 .TP
1567 .B \en[.hlc]
1568 The number of immediately preceding consecutive hyphenated lines.
1569 .TP
1570 .B \en[.hlm]
1571 The maximum allowed number of consecutive hyphenated lines, as set by the
1572 .B hlm
1573 request.
1574 .TP
1575 .B \en[.hy]
1576 The current hyphenation flags (as set by the
1577 .B hy
1578 request.)
1579 .TP
1580 .B \en[.hym]
1581 The current hyphenation margin (as set by the
1582 .B hym
1583 request.)
1584 .TP
1585 .B \en[.hys]
1586 The current hyphenation space (as set by the
1587 .B hys
1588 request.)
1589 .TP
1590 .B \en[.in]
1591 The indent that applies to the current output line.
1592 .TP
1593 .B \en[.kern]
1594 .B 1
1595 if pairwise kerning is enabled,
1596 .B 0
1597 otherwise.
1598 .TP
1599 .B \en[.lg]
1600 The current ligature mode (as set by the
1601 .B lg
1602 request.)
1603 .TP
1604 .B \en[.ll]
1605 The line length that applies to the current output line.
1606 .TP
1607 .B \en[.lt]
1608 The title length as set by the
1609 .B lt
1610 request.
1611 .TP
1612 .B \en[.ne]
1613 The amount of space that was needed in the last
1614 .B ne
1615 request that caused a trap to be sprung.
1616 Useful in conjunction with the
1617 .B \en[.trunc]
1618 register.
1619 .TP
1620 .B \en[.pn]
1621 The number of the next page:
1622 either the value set by a
1623 .B pn
1624 request, or the number of the current page plus 1.
1625 .TP
1626 .B \en[.ps]
1627 The current pointsize in scaled points.
1628 .TP
1629 .B \en[.psr]
1630 The last-requested pointsize in scaled points.
1631 .TP
1632 .B \en[.rj]
1633 The number of lines to be right-justified as set by the
1634 .B rj
1635 request.
1636 .TP
1637 .B \en[.sr]
1638 The last requested pointsize in points as a decimal fraction.
1639 This is a string-valued register.
1640 .TP
1641 .B \en[.tabs]
1642 A string representation of the current tab settings suitable for use as
1643 an argument to the
1644 .B ta
1645 request.
1646 .TP
1647 .B \en[.trunc]
1648 The amount of vertical space truncated by the most recently sprung
1649 vertical position trap, or,
1650 if the trap was sprung by a
1651 .B ne
1652 request,
1653 minus the amount of vertical motion produced by the
1654 .B ne
1655 request.
1656 In other words, at the point a trap is sprung, it represents the difference
1657 of what the vertical position would have been but for the trap,
1658 and what the vertical position actually is.
1659 Useful in conjunction with the
1660 .B \en[.ne]
1661 register.
1662 .TP
1663 .B \en[.ss]
1664 .TQ
1665 .B \en[.sss]
1666 These give the values of the parameters set by the
1667 first and second arguments of the
1668 .B ss
1669 request.
1670 .TP
1671 .B \en[.vpt]
1672 1 if vertical position traps are enabled, 0 otherwise.
1673 .TP
1674 .B \en[.warn]
1675 The sum of the numbers associated with each of the currently enabled
1676 warnings.
1677 The number associated with each warning is listed in the `Warnings'
1678 subsection.
1679 .TP
1680 .B \en(.x
1681 The major version number.
1682 For example, if the version number is
1683 .B 1.03
1684 then
1685 .B \en(.x
1686 will contain
1687 .BR 1 .
1688 .TP
1689 .B \en(.y
1690 The minor version number.
1691 For example, if the version number is
1692 .B 1.03
1693 then
1694 .B \en(.y
1695 will contain
1696 .BR 03 .
1697 .TP
1698 .B \en(.Y
1699 The revision number of groff.
1700 .TP
1701 .B \en[llx]
1702 .TQ
1703 .B \en[lly]
1704 .TQ
1705 .B \en[urx]
1706 .TQ
1707 .B \en[ury]
1708 These four registers are set by the
1709 .B \&.psbb
1710 request and contain the bounding box values (in PostScript units) of a given
1711 PostScript image.
1712 .LP
1713 The following registers are set by the
1714 .B \ew
1715 escape sequence:
1716 .TP
1717 .B \en[rst]
1718 .TQ
1719 .B \en[rsb]
1720 Like the
1721 .B st
1722 and
1723 .B sb
1724 registers, but takes account of the heights and depths of characters.
1725 .TP
1726 .B \en[ssc]
1727 The amount of horizontal space (possibly negative) that should
1728 be added to the last character before a subscript.
1729 .TP
1730 .B \en[skw]
1731 How far to right of the center of the last character
1732 in the
1733 .B \ew
1734 argument,
1735 the center of an accent from a roman font should be placed over that character.
1736 .LP
1737 The following read/write number registers are available:
1738 .TP
1739 .B \en[systat]
1740 The return value of the system() function executed by the last
1741 .B sy
1742 request.
1743 .TP
1744 .B \en[slimit]
1745 If greater than 0, the maximum number of objects on the input stack.
1746 If less than or equal to 0, there is no limit on the number of objects
1747 on the input stack. With no limit, recursion can continue until
1748 virtual memory is exhausted.
1749 .TP
1750 .B \en[year]
1751 The current year.
1752 Note that the traditional
1753 .B troff
1754 number register
1755 .B \en(yr
1756 is the current year minus 1900.
1757 .SS Miscellaneous
1758 .B @g@troff
1759 predefines a single (read/write) string-based register,
1760 .BR \e*(.T ,
1761 which contains the argument given to the
1762 .B -T
1763 command line option, namely the current output device (for example,
1764 .I latin1
1765 or
1766 .IR ascii ).
1767 Note that this is not the same as the (read-only) number register
1768 .B \en(.T
1769 which is defined to be\ 1 if
1770 .B troff
1771 is called with the
1772 .B -T
1773 command line option, and zero otherwise. This behaviour is different to
1774 Unix troff.
1775 .LP
1776 Fonts not listed in the
1777 .SM DESC
1778 file are automatically mounted on the next available font position
1779 when they are referenced.
1780 If a font is to be mounted explicitly with the
1781 .B fp
1782 request on an unused font position,
1783 it should be mounted on the first unused font position,
1784 which can be found in the
1785 .B \en[.fp]
1786 register;
1787 although
1788 .B troff
1789 does not enforce this strictly,
1790 it will not allow a font to be mounted at a position whose number is much
1791 greater than that of any currently used position.
1792 .LP
1793 Interpolating a string does not hide existing macro arguments.
1794 Thus in a macro, a more efficient way of doing
1795 .IP
1796 .BI . xx\ \e\e$@
1797 .LP
1798 is
1799 .IP
1800 .BI \e\e*[ xx ]\e\e
1801 .LP
1802 If the font description file contains pairwise kerning information,
1803 characters from that font will be kerned.
1804 Kerning between two characters can be inhibited by placing a
1805 .B \e&
1806 between them.
1807 .LP
1808 In a string comparison in a condition,
1809 characters that appear at different input levels
1810 to the first delimiter character will not be recognised
1811 as the second or third delimiters.
1812 This applies also to the
1813 .B tl
1814 request.
1815 In a
1816 .B \ew
1817 escape sequence,
1818 a character that appears at a different input level to
1819 the starting delimiter character will not be recognised
1820 as the closing delimiter character.
1821 When decoding a macro argument that is delimited
1822 by double quotes, a character that appears at a different
1823 input level to the starting delimiter character will not
1824 be recognised as the closing delimiter character.
1825 The implementation of
1826 .B \e$@
1827 ensures that the double quotes surrounding an argument
1828 will appear the same input level, which will be different
1829 to the input level of the argument itself.
1830 In a long escape name
1831 .B ]
1832 will not be recognized as a closing delimiter except
1833 when it occurs at the same input level as the opening
1834 .BR ] .
1835 In compatibility mode, no attention is paid to the input-level.
1836 .LP
1837 There are some new types of condition:
1838 .TP
1839 .BI .if\ r xxx
1840 True if there is a number register named
1841 .IR xxx .
1842 .TP
1843 .BI .if\ d xxx
1844 True if there is a string, macro, diversion, or request named
1845 .IR xxx .
1846 .TP
1847 .BI .if\ c ch
1848 True if there is a character
1849 .IR ch
1850 available;
1851 .I ch
1852 is either an
1853 .SM ASCII
1854 character
1855 or a special character
1856 .BI \e( xx
1857 or
1858 .BI \e[ xxx ]\fR;
1859 the condition will also be true if
1860 .I ch
1861 has been defined by the
1862 .B char
1863 request.
1864 .SS Warnings
1865 The warnings that can be given by
1866 .B troff
1867 are divided into the following categories.
1868 The name associated with each warning is used by the
1869 .B \-w
1870 and
1871 .B \-W
1872 options;
1873 the number is used by the
1874 .B warn
1875 request, and by the
1876 .B .warn
1877 register.
1878 .nr x \w'\fBright-brace'+1n+\w'0000'u
1879 .ta \nxuR
1880 .TP \nxu+3n
1881 .BR char \t1
1882 Non-existent characters.
1883 This is enabled by default.
1884 .TP
1885 .BR number \t2
1886 Invalid numeric expressions.
1887 This is enabled by default.
1888 .TP
1889 .BR break \t4
1890 In fill mode, lines which could not be broken so that their length was
1891 less than the line length.
1892 This is enabled by default.
1893 .TP
1894 .BR delim \t8
1895 Missing or mismatched closing delimiters.
1896 .TP
1897 .BR el \t16
1898 Use of the
1899 .B el
1900 request with no matching
1901 .B ie
1902 request.
1903 .TP
1904 .BR scale \t32
1905 Meaningless scaling indicators.
1906 .TP
1907 .BR range \t64
1908 Out of range arguments.
1909 .TP
1910 .BR syntax \t128
1911 Dubious syntax in numeric expressions.
1912 .TP
1913 .BR di \t256
1914 Use of
1915 .B di
1916 or
1917 .B da
1918 without an argument when there is no current diversion.
1919 .TP
1920 .BR mac \t512
1921 Use of undefined strings, macros and diversions.
1922 When an undefined string, macro or diversion is used,
1923 that string is automatically defined as empty.
1924 So, in most cases, at most one warning will be given for
1925 each name.
1926 .TP
1927 .BR reg \t1024
1928 Use of undefined number registers.
1929 When an undefined number register is used,
1930 that register is automatically defined to have a value of 0.
1931 a definition is automatically made with a value of 0.
1932 So, in most cases, at most one warning will be given for
1933 use of a particular name.
1934 .TP
1935 .BR tab \t2048
1936 Inappropriate use of a tab character.
1937 Either use of a tab character where a number was expected,
1938 or use of tab character in an unquoted macro argument.
1939 .TP
1940 .BR right-brace \t4096
1941 Use of
1942 .B \e}
1943 where a number was expected.
1944 .TP
1945 .BR missing \t8192
1946 Requests that are missing non-optional arguments.
1947 .TP
1948 .BR input \t16384
1949 Illegal input characters.
1950 .TP
1951 .BR escape \t32768
1952 Unrecognized escape sequences.
1953 When an unrecognized escape sequence is encountered,
1954 the escape character is ignored.
1955 .TP
1956 .BR space \t65536
1957 Missing space between a request or macro and its argument.
1958 This warning will be given
1959 when an undefined name longer than two characters is encountered,
1960 and the first two characters of the name make a defined name.
1961 The request or macro will not be invoked.
1962 When this warning is given, no macro is automatically defined.
1963 This is enabled by default.
1964 This warning will never occur in compatibility mode.
1965 .TP
1966 .BR font \t131072
1967 Non-existent fonts.
1968 This is enabled by default.
1969 .TP
1970 .BR ig \t262144
1971 Illegal escapes in text ignored with the
1972 .B ig
1973 request.
1974 These are conditions that are errors when they do not occur
1975 in ignored text.
1976 .LP
1977 There are also names that can be used to refer to groups of warnings:
1978 .TP
1979 .B all
1980 All warnings except
1981 .BR di ,
1982 .B mac
1983 and
1984 .BR reg .
1985 It is intended that this covers all warnings
1986 that are useful with traditional macro packages.
1987 .TP
1988 .B w
1989 All warnings.
1990 .SS Incompatibilities
1991 .LP
1992 Long names cause some incompatibilities.
1993 Unix troff will interpret
1994 .IP
1995 .B
1996 \&.dsabcd
1997 .LP
1998 as defining a string
1999 .B ab
2000 with contents
2001 .BR cd .
2002 Normally, GNU troff will interpret this as a call of a macro named
2003 .BR dsabcd .
2004 Also Unix troff will interpret
2005 .B \e*[
2006 or
2007 .B \en[
2008 as references to a string or number register called
2009 .BR [ .
2010 In GNU troff, however, this will normally be interpreted as the start
2011 of a long name.
2012 In
2013 .I compatibility mode
2014 GNU troff will interpret these things in the traditional way.
2015 In compatibility mode, however, long names are not recognised.
2016 Compatibility mode can be turned on with the
2017 .B \-C
2018 command line option, and turned on or off with the
2019 .B cp
2020 request.
2021 The number register
2022 .B \en(.C
2023 is 1 if compatibility mode is on, 0 otherwise.
2024 .LP
2025 GNU troff
2026 does not allow the use of the escape sequences
2027 .BR \\e\e|\e^\e&\e}\e{\e (space) \e'\e`\e-\e_\e!\e%\ec
2028 in names of strings, macros, diversions, number registers,
2029 fonts or environments; Unix troff does.
2030 The
2031 .B \eA
2032 escape sequence may be helpful in avoiding use of these
2033 escape sequences in names.
2034 .LP
2035 Fractional pointsizes cause one noteworthy incompatibility.
2036 In Unix troff the
2037 .B ps
2038 request ignores scale indicators and so
2039 .IP
2040 .B .ps\ 10u
2041 .LP
2042 will set the pointsize to 10 points, whereas in
2043 GNU troff it will set the pointsize to 10 scaled points.
2044 .LP
2045 In GNU troff there is a fundamental difference between unformatted,
2046 input characters, and formatted, output characters.
2047 Everything that affects how an output character
2048 will be output is stored with the character; once an output
2049 character has been constructed it is unaffected by any subsequent
2050 requests that are executed, including
2051 .BR bd ,
2052 .BR cs ,
2053 .BR tkf ,
2054 .BR tr ,
2055 or
2056 .B fp
2057 requests.
2058 Normally output characters are constructed from input
2059 characters at the moment immediately before the character
2060 is added to the current output line.
2061 Macros, diversions and strings are all, in fact, the same type
2062 of object; they contain lists of input characters and output
2063 characters in any combination.
2064 An output character does not behave like an input character
2065 for the purposes of macro processing; it does not inherit any
2066 of the special properties that the input character from which it
2067 was constructed might have had.
2068 For example,
2069 .IP
2070 .nf
2071 .ft B
2072 \&.di x
2073 \e\e\e\e
2074 \&.br
2075 \&.di
2076 \&.x
2077 .ft
2078 .fi
2079 .LP
2080 will print
2081 .B \e\e
2082 in GNU troff;
2083 each pair of input
2084 .BR \e s
2085 is turned into one output
2086 .B \e
2087 and the resulting output
2088 .BR \e s
2089 are not interpreted as escape characters when they are reread.
2090 Unix troff would interpret them as escape characters
2091 when they were reread and would end up printing one
2092 .BR \e .
2093 The correct way to obtain a printable
2094 .B \e
2095 is to use the
2096 .B \ee
2097 escape sequence: this will always print a single instance of the
2098 current escape character, regardless of whether or not it is used in a
2099 diversion; it will also work in both GNU troff and Unix troff.
2100 If you wish for some reason to store in a diversion an escape
2101 sequence that will be interpreted when the diversion is reread,
2102 you can either use the traditional
2103 .B \e!
2104 transparent output facility, or, if this is unsuitable, the new
2105 .B \e?
2106 escape sequence.
2107 .SH ENVIRONMENT
2108 .TP
2109 .SM
2110 .B GROFF_TMAC_PATH
2111 A colon separated list of directories in which to search for
2112 macro files.
2113 .TP
2114 .SM
2115 .B GROFF_TYPESETTER
2116 Default device.
2117 .TP
2118 .SM
2119 .B GROFF_FONT_PATH
2120 A colon separated list of directories in which to search for the
2121 .BI dev name
2122 directory.
2123 .B troff
2124 will search in directories given in the
2125 .B \-F
2126 option before these, and in standard directories
2127 .RB ( @FONTPATH@ )
2128 after these.
2129 .SH FILES
2130 .Tp \w'@FONTDIR@/devname/DESC'u+3n
2131 .B @MACRODIR@/troffrc
2132 Initialization file (called before any other macro package).
2133 .TP
2134 .B @MACRODIR@/troffrc-end
2135 Initialization file (called after any other macro package).
2136 .TP
2137 .BI @MACRODIR@/tmac. name
2138 Macro files
2139 .TP
2140 .BI @FONTDIR@/dev name /DESC
2141 Device description file for device
2142 .IR name .
2143 .TP
2144 .BI @FONTDIR@/dev name / F
2145 Font file for font
2146 .I F
2147 of device
2148 .IR name .
2149 .SH "SEE ALSO"
2150 .BR groff (@MAN1EXT@),
2151 .BR @g@tbl (@MAN1EXT@),
2152 .BR @g@pic (@MAN1EXT@),
2153 .BR @g@eqn (@MAN1EXT@),
2154 .BR @g@refer (@MAN1EXT@),
2155 .BR @g@soelim (@MAN1EXT@),
2156 .BR @g@grn (@MAN1EXT@),
2157 .BR grops (@MAN1EXT@),
2158 .BR grodvi (@MAN1EXT@),
2159 .BR grotty (@MAN1EXT@),
2160 .BR grohtml (@MAN1EXT@),
2161 .BR grolj4 (@MAN1EXT@),
2162 .BR groff_font (@MAN5EXT@),
2163 .BR groff_out (@MAN5EXT@),
2164 .BR groff_char (@MAN7EXT@)