unroff(1) unroff(1)
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NAME
unroff - programmable, extensible troff translator
SYNOPSIS
unroff [ -fformat ] [ -mpackage ] [ -hheapsize ] [ -C ]
[ -t ] [ file | option... ]
OVERVIEW
unroff reads and parses documents with embedded troff markup and
translates them to a different format-typically to a different markup
language such as SGML. The actual output format is not hard-wired
into unroff; instead, the translation is performed by a set of user-
supplied rules and functions written in the Scheme programming
language. unroff employs the Extension Language Kit Elk to achieve
programmability based on the Scheme language: a fully-functional
Scheme interpreter is embedded in the translator. The documents that
can be processed by unroff are not restricted to a specific troff
macro set. Translation rules for a new macro package can be added by
supplying a set of corresponding Scheme procedures (a back-end).
Predefined sets of such procedures exist for a number of combinations
of target language and troff macro package: unroff 1.0 supports
translation to the Hypertext Markup Language (HTML) version 2.0 for
the -man and -ms macro packages as well as bare troff (see unroff-
html(1), unroff-html-man(1), and unroff-html-ms(1) for a description).
Unlike conventional troff conversion tools, unroff includes a full
troff parser and can therefore handle user-defined macros, strings,
and number registers, nested if-else requests (with text blocks
enclosed by `\{' and `\}' escape sequences), arbitrary fonts and font
positions, troff copy mode, low-level formatting requests such as `\l'
and '\h', and the subtle differences between request and macro
invocations that are inherent in the troff processing model. unroff
has adopted a number of troff extensions introduced by groff, among
them long names for macros, strings, number registers, and special
characters, and the `\$@' and `\$*' escape sequences. unroff
interprets its input stream as a sequence of events. Events include
the invocation of a troff request or macro, the use of a troff escape
sequence or special character, a troff string or number register
reference, end of sentence, start of a new input file, and so on. For
each event encountered unroff invokes a Scheme procedure associated
with that event. Some types of events require a procedure that
returns a string (or an object that can be coerced into a string),
which is then interpolated into the input or output stream; for other
types of events, the event procedures are just called for their side-
effects. The set of Scheme procedures to be used by unroff is
determined by the output format and the name of the troff macro
package. In addition, users can supply event procedures for their own
macro definitions (or replace existing ones) in form of a simple
Scheme program passed to unroff along with the troff input files;
Scheme code can even be directly embedded in the troff input as
described below. The full capabilities of unroff and the Scheme
primitives required to write extensions or support for new output
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formats are described in the Unroff Programmer's Manual.
GENERIC OPTIONS
-fformat
Specifies the output format into which the troff input files are
translated. If no -f option is given, a default output format is
used (for unroff version 1.0 the default is -fhtml). This
default can be overridden by setting the environment variable.
-mname
Specifies the name of the macro package that would be used by
ordinary troff to typeset the document. In contrast to troff
unroff does not actually load the macro package. Instead, the
specified name-in combination with the specified output
format-selects a set of Scheme files providing the procedure
definitions that control the translation process (see FILES
below). Therefore a corresponding tmac file need not exist for a
given -m option.
-hheapsize
This option can be used to specify a non-standard heap size (in
Kbytes) for the Scheme interpreter included in unroff; see
elk(1).
-C Enables troff compatibility mode. In compatibility mode certain
groff extensions such as long names are not recognized.
-t Enables test mode. Instead of processing troff input files,
unroff enters an interactive Scheme top-level. This can be
useful to interactively experiment with the Scheme primitives
defined by unroff or to test or debug user-defined Scheme
procedures.
KEYWORD/VALUE OPTIONS
In addition to the generic options, a set of output-format-specific
options can be set from the command line and from within troff and
Scheme input files. When specified on the command line, these options
have the form
option=value
where the format of value depends on the type of the option. For
example, most output formats defines an option document whose value is
used as a prefix for all output files created during the translation.
The option is assigned a value by specifying a token such as
document=thesis
on the command line. This option's value is interpreted as a plain
string, i.e. its type is string. The Scheme back-ends and user-
supplied extensions can define their own option types, but at least
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the following types are recognized:
integer the option value is composed of an optional sign and an
(arbitrary) string of digits
boolean the option value must either be the character 1 (true) or
the character 0 (false)
character a single character must be specified as the option value
string an arbitrary string of characters can be specified
dynstring dynamic string; the option value is either
string
to assign a string to the option in the normal way, or
+string
to append the characters after the plus sign to the
option's current value, or
-string
to remove the characters after the minus sign from the
option's current value.
These extension-specific options must appear after the generic unroff
options and may be mixed with the file name arguments. As the option
assignments and specified input files are processed in order, the
value given for an option is in effect for all the input files that
appear on the command line to the right of the option. The exact set
of keyword/value options is determined by the Scheme code loaded for a
given combination of output format and macro package name and is
described in the corresponding manuals. The following few options can
always be set, regardless of the actual output format:
include-files (boolean)
If true, .so requests are executed by unroff in the normal
way (that is, the named input file is read and parsed),
otherwise .so requests are ignored. The default value is 1.
if-true (dynstring)
the specified characters are assigned to (appended to,
removed from) the set of one-character conditions that are
regarded as true by the .if and .ie requests. The default
value is "to".
if-false (dynstring)
like if-true; specifies the one-character conditions
regarded as false. The default value is "ne".
FILES
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INPUT FILES
On startup, unroff loads the Scheme source files that control the
translation process. All these files are loaded from subdirectories
of a site-specific library directory, typically something like
/usr/local/lib/unroff. The directory is usually chosen by the system
administrator when installing the software and can be overridden by
setting the environment variable. The path names mentioned in the
following are relative to this library directory. The first Scheme
file loaded is scm/troff.scm which contains basic definitions such as
the built-in options and option types, implementations for troff
requests that are not output-format specific, and utility functions to
be used by the back-ends or by user-supplied extensions. Next, the
file scm/format/common.scm is loaded, where format is the value of the
option -f as given on the command line (or its default value). The
file implements the translation of the basic troff requests, escape
sequences, and special characters, etc. The code dealing with macro
invocations is loaded from scm/format/package.scm where package is the
value of the option -m with the letter `m' prepended. Finally, the
file .unroff is loaded from the caller's home directory if present.
Arbitrary Scheme code can be placed in this initialization file. It
is typically used to assign values to package-specific keyword/value
options according to the user's preferences (by means of the set-
option! Scheme primitive as explained in the Programmer's Manual).
When the initial files have been loaded, any troff input files
specified in the command line are read and parsed. The special file
name `-' can be used to indicate standard input (usually in
combination with ordinary file names). If no file name is given,
unroff reads from standard input. In addition to troff input files,
file containing Scheme code can be mentioned in the command line.
Scheme files (which by convention end in .scm) are loaded into the
Scheme interpreter and usually contain used-defined Scheme procedures
to translate specific macros or to replace existing procedures, or
other user-supplied extensions of any kind. Scheme files named in the
command line (or loaded explicitly from within other files) are
resolved against the directory scm/misc/ which may hold site-specific
extensions or other supplementary packages. troff files and Scheme
files can be mixed freely in the command line.
OUTPUT FILES
Whether unroff sends its output to standard output or produces one or
more output files is not hard-wired but determined by the combination
of output format and macro package. Generally, if no troff input
files are specified, output is directed to standard output, but this
rule is not mandatory and may be overridden by specific back-ends.
The document option is usually honored, although other rules may be
employed to determine the names of output files (for example, the
extension that implements -man for a given output format may derive
the name of the output file for a manual page from the input file
name; see unroff-html-man(1)). If unroff is interrupted or quits
early, any output files produced so far may be incomplete or may
contain wrong or inconsistent data, because several passes may be
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required to complete an output file (for example, to resolve cross
references between a set of files), or because an output file is not
necessarily produced as a whole, but unroff may work on several files
simultaneously.
EXAMPLES
To translate a troff document composed of two files and written with
the ms macro package to HTML 2.0, unroff might be called like this:
unroff -fhtml -ms doc.tr doc.tr
Two options specific to the combination of -fhtml and -ms might be
added to specify a prefix for output files and to have the resulting
output split into separate files after each section (see unroff-html-
ms(1)):
unroff -fhtml -ms document=out/ split=1 doc.tr doc.tr
Additional features may be loaded from Scheme files specified in the
command line, e.g. hyper.scm which implements general Hypertext
requests (and gets loaded from scm/misc/) and a user-supplied file in
the current directory providing translation rules for user-defined
troff macros:
unroff -fhtml -ms document=out/ split=1 hyper.scm doc.scm\
doc.tr doc.tr
TROFF SUPPORT AND EXTENSIONS
As unroff translates troff input into another language rather than
typesetting the text in the usual way, its processing model
necessarily differs from that of conventional troff. For a detailed
description refer to the Programmer's Manual. In brief, unroff copies
characters from input to output, optionally performing target-
language-specific character translations. For each request or macro
invocation, string or number register reference, special character,
escape sequence, sentence end, or eqn(1) inline equation encountered
in the input stream, unroff checks whether an event value has been
specified by the Scheme code (user-supplied or part of the back-end).
An event value is either a plain string, which is then treated as if
it had been part of the input stream, or a Scheme procedure, which is
then invoked and must in turn return a string. The Scheme procedures
are passed arguments, e.g. the macro or request arguments in case of a
procedure attached to a macro or request, or an escape sequence
argument for functions such as `\f' or `\w'. If no event value has
been associated with a particular macro, string, or number register,
unroff checks whether a definition has been supplied in the normal
way, i.e. by means of .de, .ds, or .nr. In this case, the value of
the macro, string, or register is interpolated as done by ordinary
troff. If no definition can be found, a fallback definition is looked
up as a last resort; and if everything fails, a warning is printed and
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the event is ignored. Similarly, event procedures are invoked at end
of input line, when an input file is opened or closed, at program
start and termination, and for each option specified in the command
line; but these procedures are called solely for their side-effects
(i.e. the return values are ignored). Most Scheme procedures just
emit the target language's representation of the event with which they
are associated. Other procedures perform various kinds of
bookkeeping; the procedure associated with the .de request, for
example, puts the text following aside for later expansion, and the
event procedures attached to the requests .ds and .nr and to the
escape sequences `\*' and `\n' implement troff strings and number
registers. This way, even basic troff functions need not be hard-
wired and can be altered or replaced freely without recompiling
unroff. The rule that an event value associated with a macro has
precedence over the actual macro definition accommodates higher-level,
structure-oriented target languages (such as SGML). While the micro-
formatting contained in a typical -ms macro definition, for example,
makes sense to an ordinary typesetting program, it is usually
impossible to infer the macro's structural function from it (new
paragraph, quotation, etc.). On the other hand, troff documents often
define a few additional, simple macros that just serve as an
abbreviation for a sequence of predefined macros; in this case event
procedures need not specified, as unroff will then perform normal
macro expansion. unroff usually takes care to not rescan the
characters returned by event procedures as if their results had been
normal input, because most event procedures already return code in the
target language rather than troff input that can be rescanned. This,
however, cannot always be avoided; for example, if a troff string
reference occurs at macro definition time (because `\*' is used rather
than `\\*'), the string value ends up in the macro body and will still
be rescanned when the macro is invoked. A few other pitfalls caused
by differences in the processing models of troff and unroff are listed
in the BUGS section below. The scaling performed for the usual troff
scale indicators can be manipulated by a calling a Scheme primitive
from within the Scheme code implementing a particular back-end.
NEW TROFF REQUESTS
To aid transparent output of code in the target language and
evaluation of inline Scheme code, unroff supports two new requests and
two extensions to the .ig (ignore input lines) troff request. If .ig
is called with the symbol >> as its first argument, all input lines up
to (but not including) the terminating .>> are sent to the current
output file. Example: when translating to the Hypertext Markup
Language, the construct could be used to emit literal HTML code like
this:
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.ig >>
<address>
Bart Simpson<br>
Springfield
</address>
.>>
To produce a single line of output, the new request .>> can be used as
in this HTML example:
.>> "<code>result = i+1;</code>"
If the .ig request is called with the argument ##, everything up to
the terminating .## is passed to the Scheme interpreter for
evaluation. This allows users to embed Scheme code in a troff
document which is executed when the document is processed by unroff.
One use of this construct is to provide a Scheme event procedure for a
user-defined macro by placing the corresponding Scheme definition in
the same source file right below the troff macro definition.
Similarly, the request .## can be used to evaluate a short S-
expression; all arguments to the request are concatenated and then
passed to the Scheme interpreter. Note that inline Scheme code is a
potentially dangerous feature, as a document received by someone else
may contain embedded code that does something unexpected when the file
is processed by unroff (but it is probably not more dangerous than the
standard troff .pi request or the .sy request of ditroff). unroff
defines the following new read-only number registers:
.U This register always expand to 1. It can be used by macros to
determine whether the document is being processed by unroff.
.C Expands to 1 if troff compatibility mode has been enabled by
using the option -C, to 0 otherwise. The following new escape
sequences are available in a macro body during macro expansion:
$0 The name of the current macro.
$* The concatenation of all arguments, separated by spaces.
$@ The concatenation of all arguments, separated by spaces, and with
each argument enclosed by double quotes. The names of strings,
macros, number registers, and fonts may be of any length. As in
groff, square brackets can be used for names of arbitrary length:
\f[font] \*[string] \n[numreg] ...
There is no limit on the number of macro arguments, and the following
syntax can be used to reference the 10th, 11th, etc. macro argument:
\$(12 \$[12] \$[123]
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Unless troff compatibility mode has been enabled, the arguments to the
groff-specific escape sequences `\A', `\C', '\L', '\N', '\R', '\V',
'\Y', and '\Z' are recognized and parsed, so that event procedures can
be implemented correctly for these escape sequences.
SEE ALSO
unroff-html(1), unroff-html-man(1), unroff-html-ms(1);
troff(1), groff(1); elk(1). Unroff Programmer's Manual.
http://www.informatik.uni-bremen.de/~net/unroff
AUTHOR
Oliver Laumann, net@cs.tu-berlin.de
BUGS
A number of low-level formatting features of troff (such as the
absolute position indicator in numerical expressions) are not yet
supported by unroff version 1.0, which is not critical for higher-
level, structure-oriented target languages such as the Hypertext
Markup Language. Diversions are not supported, although specific
back-ends are free to add this functionality. Special characters are
not treated right in certain contexts; in particular, special
characters may not be used in place of plain characters where the
characters act as some kind of delimiter as in
.if \(bsfoo\(bsbar\(bs ...
Spaces in an .if condition do not work; e.g. the following fails:
.if ' ' ' ...
Conditional input is subject to string and number register expansion
even if the corresponding if-condition evaluates to false. There are
no number register formats, i.e. the request .af does not work. The
set of punctuation marks that indicate end of sentence should be
configurable. Empty input lines and leading space should trigger a
special event, so that their break semantics can be implemented
correctly. A comment in a line by itself currently does not generate
a blank line.
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