grn(1)

💅 grn(1) 💅

okay bestie, this page is from the General Commands Manual, and it’s all about grn, the preprocessor that yeets Gremlin pictures into your groff docs. 🎀

✨ 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 💖

okay so grn is a preprocessor for including gremlin pictures in troff(1) input. It 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. no cap, that part matters 💀

🦋 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. iykyk, short and sweet ✨

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 — Set gremlin's text size number 1 to N points. The default is 12.
• 2 N — Set gremlin's text size number 2 to N points. The default is 16.
• 3 N — Set gremlin's text size number 3 to N points. The default is 24.
• 4 N — Set gremlin's text size number 4 to N points. The default is 36.
• roman f — Set the roman font to troff's font f (either a name or number). The default is R.
• italics f — Set the italics font to troff's font f (either a name or number). The default is I.
• bold f — Set the bold font to troff's font f (either a name or number). The default is B.
• special f — Set the special font to troff's font f (either a name or number). The default is S.
• 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., “$$”). that’s lowkey iconic 🧚

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. order matters, bestie 💛

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

• The first line of each gremlin file contains either the string “gremlinfile” (AED) or “sungremlinfile” (Sun/X11).
• 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.
• The rest of the file consists of zero or more element specifications. After the last element specification is a line containing the string “-1”.
• Lines longer than 127 characters are truncated to that length.

🌟 Element specifications 🌟

• 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 🎀

Here’s the AED Number ↔ Sun/X11 Name ↔ Description mapping:

• 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 — Bézier
• 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
• 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).
• 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
• 🫶 and hey, 0 is a whole valid mood for polygons too — it literally just means "invisible border". No cap. For text, tho, that brush field picks you a font, like:
  1. roman (R font in troff)
  2. italics (I font in troff)
  3. bold (B font in troff)
  4. special (S font in troff)
• ✨ So if you're using grn to run your pics through groff, the font is really just a starting font, okay? The text string can carry formatting sequences like \fI or \d which may change the font (and also do a whole bunch of other things, she's versatile 💅).
• For text, the size field is a decimal value between 1 and 4. It picks the size of the font the text gets drawn in. For polygons, that same size field gets interpreted as a stipple number to fill the polygon with — the number indexes into a stipple font at print time. Iconic behaviour honestly.
• 🎀 The last line of every element has a decimal number and a string of characters, separated by a single space. The number is a count of how many characters are in the string. This info is used only for text elements, and it holds the text string itself. There can be spaces inside the text, bestie — it's fine. For arcs, curves, and vectors, the character count is zero (0), followed by exactly one space before the newline. Exactly one. Don't get creative with it 🙈.

🗺️ Coordinates

gremlin was designed for AED terminals, and its coordinates reflect the AED coordinate space, periodt.

• 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.

You don't absolutely have to stick to that range, but ngl you'll get better results if you at least stay in the vicinity. Also — point lists are terminated by a point of (-1, -1), so you should never ever use negative coordinates. gremlin writes out coordinates using the printf(3) format %f1.2; it's probably a good idea to use that same format if you want to modify the grn code. Consistency slays 💖

☀️ Sun/X11 coordinates

There is no restriction on the range of coordinates used to create objects in the Sun/X11 version of gremlin. Freedom! 🌈

But fr fr — files with negative coordinates will cause problems if displayed on the AED. So like, know your audience 💀

✨ OPTIONS ✨

• -? and --help — display a usage message. Both exit afterward.
• -v and --version — show version information. Also exits afterward. (Yes, all of these bounce right after doing their one job 👑)
• -C — recognize .GS and .GE (and .GF) even when they're followed by a character other than a 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 /usr/share/groff/site-font, /usr/share/groff/1.24.2/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, /usr/share/groff/site-tmac, and /usr/share/groff/1.24.2/tmac, in that order. Order matters, bestie 🫶
• -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 😭
• status 1 if it encounters an error during operation 💀

📂 FILES

• /usr/share/groff/1.24.2/font/devname/DESC — describes the output device name.

👑 AUTHORS

David Slattengren and Barry Roitblat wrote the original Berkeley grn. Daniel Senderowicz and Werner Lemberg modified it for groff. Legends, all of them 🎀

🦋 SEE ALSO

gremlin(1), groff(1), pic(1), ideal(1) — go read the whole friend group ✨

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And that's the whole page, bestie! This masterpiece is groff 1.24.2, dated 2026-10-01, and it's grn(1) — go make some iconic little diagrams with it 💜💅