grn(1) General Commands Manual grn(1)
Name
grn - embed Gremlin images in groff documents
Synopsis
grn [-C] [-T dev] [-M dir] [-F dir] [file ...]
grn -?
grn --help
grn -v
grn --version
Description
grn is a preprocessor for including gremlin pictures in troff(1) input.
grn writes to standard output, processing only input lines between two
that start with .GS and .GE. Those lines must contain grn commands
(see below). These macros request a gremlin file; the picture in that
file is converted and placed in the troff input stream. .GS may be
called with a C, L, or R argument to center, left-, or right-align the
whole gremlin picture (the default is to center). If no file is
mentioned, the standard input is read. At the end of the picture, the
position on the page is the bottom of the gremlin picture. If the grn
entry is ended with .GF instead of .GE, the position is left at the top
of the picture.
Currently only the me macro package has support for .GS, .GE, and .GF.
grn produces drawing escape sequences that use groff's color scheme
extension (\D'F ...'), and thus may not work with other troffs.
grn commands
Each input line between .GS and .GE may have one grn command. Commands
consist of one or two strings separated by whitespace, the first string
being the command and the second its operand. Commands may be upper-
or lowercase and abbreviated down to one character.
Commands that affect a picture's environment (those listed before
"default", see below) are only in effect for the current picture: the
environment is reinitialized to the defaults at the start of the next
picture. The commands are as follows.
1 N
2 N
3 N
4 N Set gremlin's text size number 1 (2, 3, or 4) to N points. The
default is 12 (16, 24, and 36, respectively).
roman f
italics f
bold f
special f
Set the roman (italics, bold, or special) font to troff's font f
(either a name or number). The default is R (I, B, and S,
respectively).
l f
stipple f
Set the stipple font to troff's stipple font f (name or number).
The command stipple may be abbreviated down as far as "st" (to
avoid confusion with "special"). There is no default for
stipples (unless one is set by the "default" command), and it is
invalid to include a gremlin picture with polygons without
specifying a stipple font.
x N
scale N
Magnify the picture (in addition to any default magnification)
by N, a floating-point number larger than zero. The command
scale may be abbreviated down to "sc".
narrow N
medium N
thick N
Set the thickness of gremlin's narrow (medium and thick,
respectively) lines to N times 0.15pt (this value can be changed
at compile time). The default is 1.0 (3.0 and 5.0,
respectively), which corresponds to 0.15pt (0.45pt and 0.75pt,
respectively). A thickness value of zero selects the smallest
available line thickness. Negative values cause the line
thickness to be proportional to the current point size.
pointscale [off|on]
Scale text to match the picture. Gremlin text is usually
printed in the point size specified with the commands 1, 2, 3,
or 4, regardless of any scaling factors in the picture. Setting
pointscale will cause the point sizes to scale with the picture
(within troff's limitations, of course). An operand of anything
but off will turn text scaling on.
default
Reset the picture environment defaults to the settings in the
current picture. This is meant to be used as a global parameter
setting mechanism at the beginning of the troff input, but can
be used at any time to reset the default settings.
width N
Force the picture to be N inches wide. This overrides any
scaling factors present in the same picture. "width 0" is
ignored.
height N
Force the picture to be N inches high, overriding other scaling
factors. If both width and height are specified, the tighter
constraint will determine the scale of the picture. height and
width commands are not saved with a "default" command. They
will, however, affect point size scaling if that option is set.
file name
Get picture from gremlin file name located the current directory
(or in the library directory; see the -M option above). If
multiple file commands are given, the last one controls. If
name doesn't exist, an error message is reported and processing
continues from the .GE line.
Usage with groff
Since grn is a preprocessor, it has no access to elements of formatter
state, such as indentation, line length, type size, or register values.
Consequently, no troff input can be placed between the .GS and .GE
macros. However, gremlin text elements are subsequently processed by
troff, so anything valid in a single line of troff input is valid in a
line of gremlin text (barring the dot control character "." at the
beginning of a line). Thus, it is possible to have equations within a
gremlin figure by including in the gremlin file eqn expressions
enclosed by previously defined delimiters (e.g., "$$").
When using grn along with other preprocessors, run tbl(1) before grn,
pic(1), and/or ideal. If eqn(1) is needed, run it as the last
preprocessor. groff(1) automatically runs preprocessors in the correct
order.
A picture is considered an entity, but that doesn't stop troff from
trying to break it up if it falls off the end of a page. Placing the
picture between "keeps" in the me macros will ensure proper placement.
grn uses troff's registers g1 through g9 and sets registers g1 and g2
to the width and height of the gremlin figure (in device units) before
entering the .GS macro (this is for those who want to rewrite these
macros).
Gremlin file format
There exist two distinct gremlin file formats: the original format for
AED graphic terminals, and the Sun or X11 version. An extension used
by the Sun/X11 version allowing reference points with negative
coordinates is not compatible with the AED version. As long as a
gremlin file does not contain negative coordinates, either format will
be read correctly by either version of gremlin or grn. The other
difference in Sun/X11 format is the use of names for picture objects
(e.g., POLYGON, CURVE) instead of numbers. Files representing the same
picture are shown below.
sungremlinfile gremlinfile
0 240.00 128.00 0 240.00 128.00
CENTCENT 2
240.00 128.00 240.00 128.00
185.00 120.00 185.00 120.00
240.00 120.00 240.00 120.00
296.00 120.00 296.00 120.00
* -1.00 -1.00
2 3 2 3
10 A Triangle 10 A Triangle
POLYGON 6
224.00 416.00 224.00 416.00
96.00 160.00 96.00 160.00
384.00 160.00 384.00 160.00
* -1.00 -1.00
5 1 5 1
0 0
-1 -1
o The first line of each gremlin file contains either the string
"gremlinfile" (AED) or "sungremlinfile" (Sun/X11).
o The second line of the file contains an orientation and x and y
values for a positioning point, separated by spaces. The
orientation, either 0 or 1, is ignored by the Sun/X11 version. 0
means that gremlin will display things in horizontal format (a
drawing area wider than it is tall, with a menu across the top). 1
means that gremlin will display things in vertical format (a drawing
area taller than it is wide, with a menu on the left side). x and y
are floating-point values giving a positioning point to be used when
this file is read into another file. The stuff on this line really
isn't all that important; a value of "1 0.00 0.00" is suggested.
o The rest of the file consists of zero or more element
specifications. After the last element specification is a line
containing the string "-1".
o Lines longer than 127 characters are truncated to that length.
Element specifications
o The first line of each element contains a single decimal number
giving the type of the element (AED) or its name (Sun/X11).
gremlin File Format: Object Type Specification
----------------------------------------------------------
AED Number Sun/X11 Name Description
0 BOTLEFT text aligned to bottom left
1 BOTRIGHT text aligned to bottom right
2 CENTCENT center object
3 VECTOR vector
4 ARC arc
5 CURVE curve
6 POLYGON polygon
7 BSPLINE b-spline
8 BEZIER Bezier
10 TOPLEFT text aligned to top left
11 TOPCENT text aligned to top center
12 TOPRIGHT text aligned to top right
13 CENTLEFT text aligned to center left
14 CENTRIGHT text aligned to center right
15 BOTCENT text aligned to bottom center
o Each line after the object type specifies a point used to display
the element. It contains an x and a y coordinate in floating-point
format, separated by spaces. The list of points is terminated by a
line containing the string "-1.0 -1.0" (AED) or a single asterisk,
"*" (Sun/X11).
o After the points comes a line containing two decimal values, giving
the brush and size for the element. The brush determines the style
in which things are drawn. For vectors, arcs, and curves there are
six valid brush values.
1 thin dotted lines
2 thin dot-dashed lines
3 thick solid lines
4 thin dashed lines
5 thin solid lines
6 medium solid lines
For polygons, 0 is also valid: it specifies an invisible border.
For text, the brush selects a font as follows.
1 roman (R font in troff)
2 italics (I font in troff)
3 bold (B font in troff)
4 special (S font in troff)
If you're using grn to run your pictures through groff, the font is
really just a starting font. The text string can contain formatting
sequences like "\fI" or "\d" which may change the font (as well as
do many other things). For text, the size field is a decimal value
between 1 and 4. It selects the size of the font in which the text
will be drawn. For polygons, this size field is interpreted as a
stipple number to fill the polygon with. The number is used to
index into a stipple font at print time.
o The last line of each element contains a decimal number and a string
of characters, separated by a single space. The number is a count
of the number of characters in the string. This information is used
only for text elements, and contains the text string. There can be
spaces inside the text. For arcs, curves, and vectors, the
character count is zero (0), followed by exactly one space before
the newline.
Coordinates
gremlin was designed for AED terminals, and its coordinates reflect the
AED coordinate space. For vertical pictures, x values range 116 to
511, and y values from 0 to 483. For horizontal pictures, x values
range from 0 to 511, and y values from 0 to 367. Although you needn't
absolutely stick to this range, you'll get better results if you at
least stay in this vicinity. Also, point lists are terminated by a
point of (-1, -1), so you shouldn't ever use negative coordinates.
gremlin writes out coordinates using the printf(3) format "%f1.2"; it's
probably a good idea to use the same format if you want to modify the
grn code.
Sun/X11 coordinates
There is no restriction on the range of coordinates used to create
objects in the Sun/X11 version of gremlin. However, files with
negative coordinates will cause problems if displayed on the AED.
Options
-? and --help display a usage message, while -v and --version show
version information; all exit afterward.
-C Recognize .GS and .GE (and .GF) even when followed by a
character other than space or newline.
-F dir Search dir for subdirectories devname (name is the name of the
output driver) for the DESC file before the default font
directories /opt/local/share/groff/site-font, /opt/local/share/
groff/1.24.1/font, and /usr/lib/font.
-M dir Prepend dir to the search path for gremlin files. The default
search path is the current directory, the home directory, /opt/
local/share/groff/site-tmac, and /opt/local/share/groff/1.24.1/
tmac, in that order.
-T dev Prepare device output using output driver dev. The default is
ps. See groff(1) for a list of valid devices.
Exit status
grn exits with status 0 on successful operation, status 2 if the
program cannot interpret its command-line arguments, and status 1 if it
encounters an error during operation.
Files
/opt/local/share/groff/1.24.1/font/devname/DESC
describes the output device name.
Authors
David Slattengren and Barry Roitblat wrote the original Berkeley grn.
Daniel Senderowicz and Werner Lemberg <wl@gnu.org> modified it for
groff.
See also
gremlin(1), groff(1), pic(1), ideal(1)
groff 1.24.1 2026-05-15 grn(1)
groff 1.24.1 - Generated Mon May 18 08:19:24 CDT 2026