Manual: gpic
pic(1) General Commands Manual pic(1)
Name
pic - compile pictures for troff or TeX
Synopsis
pic [-CnSU] [file ...]
pic -t [-cCSUz] [file ...]
pic --help
pic -v
pic --version
Description
The GNU implementation of pic is part of the groff(1) document formatting system. pic is a troff(1) preprocessor
that translates descriptions of diagrammatic pictures embedded in roff(7) or TeX input files into the language under‐
stood by TeX or troff. It copies the contents of each file to the standard output stream, except that lines between
.PS and any of .PE, .PF, or .PY are interpreted as picture descriptions in the pic language. End a pic picture with
.PE to leave the drawing position at the bottom of the picture, and with .PF or .PY to leave it at the top. Nor‐
mally, pic is not executed directly by the user, but invoked by specifying the -p option to groff(1). If no file
operands are given on the command line, or if file is “-”, the standard input stream is read.
It is the user's responsibility to provide appropriate definitions of the PS, PE, and one or both of the PF and PY
macros. When a macro package does not supply these, obtain simple definitions with the groff option -mpic; these
will center each picture.
GNU pic supports PY as a synonym of PF to work around a name space collision with the mm macro package, which defines
PF as a page footer management macro. Use PF preferentially unless a similar problem faces your document.
Options
--help displays a usage message, while -v and --version show version information; all exit afterward.
-c Be more compatible with tpic; implies -t. Lines beginning with \ are not passed through transparently. Lines
beginning with . are passed through with the initial . changed to \. A line beginning with .ps is given spe‐
cial treatment: it takes an optional integer argument specifying the line thickness (pen size) in milliinches;
a missing argument restores the previous line thickness; the default line thickness is 8 milliinches. The
line thickness thus specified takes effect only when a non-negative line thickness has not been specified by
use of the thickness attribute or by setting the linethick variable.
-C Recognize .PS, .PE, .PF, and .PY even when followed by a character other than space or newline.
-n Don't use groff extensions to the troff drawing commands. Specify this option if a postprocessor you're using
doesn't support these extensions, described in groff_out(5). This option also causes pic not to use zero-
length lines to draw dots in troff mode.
-S Operate in safer mode; sh commands are ignored. This mode, enabled by default, can be useful when operating
on untrustworthy input.
-t Produce TeX output.
-U Operate in unsafe mode; sh commands are interpreted.
-z In TeX mode, draw dots using zero-length lines.
The following options supported by other versions of pic are ignored.
-D Draw all lines using the \D escape sequence. GNU pic always does this.
-T dev Generate output for the troff device dev. This is unnecessary because the troff output generated by GNU pic
is device-independent.
Usage
This section primarily discusses the differences between GNU pic and the Eighth Edition Research Unix version of AT&T
pic (1985). Many of these differences also apply to later versions of AT&T pic.
TeX mode
TeX-compatible output is produced when the -t option is specified. You must use a TeX driver that supports tpic ver‐
sion 2 specials. (tpic was a fork of AT&T pic by Tim Morgan of the University of California at Irvine that diverged
from its source around 1984. It is best known today for lending its name to a group of \special commands it produced
for TeX.)
Lines beginning with \ are passed through transparently; a % is added to the end of the line to avoid unwanted
spaces. You can safely use this feature to change fonts or the value of \baselineskip. Anything else may well pro‐
duce undesirable results; use at your own risk. By default, lines beginning with a dot are not treated specially—but
see the -c option.
In TeX mode, pic will define a vbox called \graph for each picture. Use GNU pic's figname command to change the name
of the vbox. You must print that vbox yourself using the command
\centerline{\box\graph}
for instance. Since the vbox has a height of zero (it is defined with \vtop) this will produce slightly more verti‐
cal space above the picture than below it;
\centerline{\raise 1em\box\graph}
would avoid this. To give the vbox a positive height and a depth of zero (as used by LaTeX's graphics.sty, for exam‐
ple) define the following macro in your document.
\def\gpicbox#1{%
\vbox{\unvbox\csname #1\endcsname\kern 0pt}}
You can then simply say \gpicbox{graph} instead of \box\graph.
Commands
Several commands new to GNU pic accept delimiters, shown in their synopses as braces { }. Nesting of braces is sup‐
ported. Any other characters (except a space, tab, or newline) may be used as alternative delimiters, in which case
the members of a given pair must be identical. Strings are recognized within delimiters of either kind; they may
contain the delimiter character or unbalanced braces.
for variable = expr1 to expr2 [by [*]expr3] do X body X
Set variable to expr1. While the value of variable is less than or equal to expr2, do body and increment
variable by expr3; if by is not given, increment variable by 1. If expr3 is prefixed by * then variable will
instead be multiplied by expr3. The value of expr3 can be negative for the additive case; variable is then
tested whether it is greater than or equal to expr2. For the multiplicative case, expr3 must be greater than
zero. If the constraints aren't met, the loop isn't executed. X can be any character not occurring in body.
if expr then X if-true X [else Y if-false Y]
Evaluate expr; if it is non-zero then do if-true, otherwise do if-false. X can be any character not occurring
in if-true. Y can be any character not occurring in if-false.
print arg ...
Concatenate and write arguments to the standard error stream followed by a newline. Each arg must be an ex‐
pression, a position, or text. This is useful for debugging.
command arg ...
Concatenate arguments and pass them as a line to troff or TeX. Each arg must be an expression, a position, or
text. command allows the values of pic variables to be passed to the formatter. For example,
.PS
x = 14
command ".ds string x is " x "."
.PE
\*[string]
produces
x is 14.
when formatted with troff.
sh X command X
Pass command to a shell.
copy "filename"
Include filename at this point in the file.
copy ["filename"] thru X body X [until "word"]
copy ["filename"] thru macro [until "word"]
This construct does body once for each line of filename; the line is split into blank-delimited words, and oc‐
currences of $i in body, for i between 1 and 9, are replaced by the i-th word of the line. If filename is not
given, lines are taken from the current input up to .PE. If an until clause is specified, lines will be read
only until a line the first word of which is word; that line will then be discarded. X can be any character
not occurring in body. For example,
.PS
copy thru % circle at ($1,$2) % until "END"
1 2
3 4
5 6
END
box
.PE
and
.PS
circle at (1,2)
circle at (3,4)
circle at (5,6)
box
.PE
are equivalent. The commands to be performed for each line can also be taken from a macro defined earlier by
giving the name of the macro as the argument to thru. The argument after thru is looked up as a macro name
first; if not defined, its first character is interpreted as a delimiter.
reset
reset pvar1[,] pvar2 ...
Reset predefined variables pvar1, pvar2 ... to their default values; if no arguments are given, reset all pre‐
defined variables to their default values. Variable names may be separated by commas, spaces, or both. As‐
signing a value to scale also causes all predefined variables that control dimensions to be reset to their de‐
fault values times the new value of scale.
plot expr ["text"]
This is a text object which is constructed by using text as a format string for sprintf with an argument of
expr. If text is omitted a format string of "%g" is used. Attributes can be specified in the same way as for
a normal text object. Be very careful that you specify an appropriate format string; pic does only very lim‐
ited checking of the string. This is deprecated in favour of sprintf.
var := expr
This syntax resembles variable assignment with = except that var must already be defined, and expr will be as‐
signed to var without creating a variable local to the current block. (By contrast, = defines var in the cur‐
rent block if it is not already defined there, and then changes the value in the current block only.) For ex‐
ample,
.PS
x = 3
y = 3
[
x := 5
y = 5
]
print x y
.PE
writes
5 3
to the standard error stream.
Expressions
The syntax for expressions has been significantly extended.
x ^ y (exponentiation)
sin(x)
cos(x)
atan2(y, x)
log(x) (base 10)
exp(x) (base 10, i.e. 10^x)
sqrt(x)
int(x)
rand() (return a random number between 0 and 1)
rand(x) (return a random number between 1 and x; deprecated)
srand(x) (set the random number seed)
max(e1, e2)
min(e1, e2)
!e
e1 && e2
e1 || e2
e1 == e2
e1 != e2
e1 >= e2
e1 > e2
e1 <= e2
e1 < e2
"str1" == "str2"
"str1" != "str2"
String comparison expressions must be parenthesised in some contexts to avoid ambiguity.
Other changes
A bare expression, expr, is acceptable as an attribute; it is equivalent to dir expr, where dir is the current direc‐
tion. For example
line 2i
means draw a line 2 inches long in the current direction. The ‘i’ (or ‘I’) character is ignored; to use another mea‐
surement unit, set the scale variable to an appropriate value.
The maximum width and height of the picture are taken from the variables maxpswid and maxpsht. Initially, these have
values 8.5 and 11.
Scientific notation is allowed for numbers. For example
x = 5e-2
Text attributes can be compounded. For example,
"foo" above ljust
is valid.
There is no limit to the depth to which blocks can be examined. For example,
[A: [B: [C: box ]]] with .A.B.C.sw at 1,2
circle at last [].A.B.C
is acceptable.
Arcs now have compass points determined by the circle of which the arc is a part.
Circles, ellipses, and arcs can be dotted or dashed. In TeX mode splines can be dotted or dashed also.
Boxes can have rounded corners. The rad attribute specifies the radius of the quarter-circles at each corner. If no
rad or diam attribute is given, a radius of boxrad is used. Initially, boxrad has a value of 0. A box with rounded
corners can be dotted or dashed.
Boxes can have slanted sides. This effectively changes the shape of a box from a rectangle to an arbitrary parallel‐
ogram. The xslanted and yslanted attributes specify the x and y offset of the box's upper right corner from its de‐
fault position.
The .PS line can have a second argument specifying a maximum height for the picture. If the width of zero is speci‐
fied the width will be ignored in computing the scaling factor for the picture. GNU pic will always scale a picture
by the same amount vertically as well as horizontally. This is different from DWB 2.0 pic which may scale a picture
by a different amount vertically than horizontally if a height is specified.
Each text object has an invisible box associated with it. The compass points of a text object are determined by this
box. The implicit motion associated with the object is also determined by this box. The dimensions of this box are
taken from the width and height attributes; if the width attribute is not supplied then the width will be taken to be
textwid; if the height attribute is not supplied then the height will be taken to be the number of text strings asso‐
ciated with the object times textht. Initially, textwid and textht have a value of 0.
In (almost all) places where a quoted text string can be used, an expression of the form
sprintf("format", arg, ...)
can also be used; this will produce the arguments formatted according to format, which should be a string as de‐
scribed in printf(3) appropriate for the number of arguments supplied. Only the modifiers “#”, “-”, “+”, and “ ”
[space]), a minimum field width, an optional precision, and the conversion specifiers %e, %E, %f, %g, %G, and %% are
supported.
The thickness of the lines used to draw objects is controlled by the linethick variable. This gives the thickness of
lines in points. A negative value means use the default thickness: in TeX output mode, this means use a thickness of
8 milliinches; in TeX output mode with the -c option, this means use the line thickness specified by .ps lines; in
troff output mode, this means use a thickness proportional to the pointsize. A zero value means draw the thinnest
possible line supported by the output device. Initially, it has a value of -1. There is also a thick[ness] at‐
tribute. For example,
circle thickness 1.5
would draw a circle using a line with a thickness of 1.5 points. The thickness of lines is not affected by the value
of the scale variable, nor by the width or height given in the .PS line.
Boxes (including boxes with rounded corners or slanted sides), circles and ellipses can be filled by giving them an
attribute of fill[ed]. This takes an optional argument of an expression with a value between 0 and 1; 0 will fill it
with white, 1 with black, values in between with a proportionally gray shade. A value greater than 1 can also be
used: this means fill with the shade of gray that is currently being used for text and lines. Normally this will be
black, but output devices may provide a mechanism for changing this. Without an argument, then the value of the
variable fillval will be used. Initially, this has a value of 0.5. The invisible attribute does not affect the
filling of objects. Any text associated with a filled object will be added after the object has been filled, so that
the text will not be obscured by the filling.
Additional modifiers are available to draw colored objects: outline[d] sets the color of the outline, shaded the fill
color, and colo[u]r[ed] sets both. All expect a subsequent string argument specifying the color.
circle shaded "green" outline "black"
Color is not yet supported in TeX mode. Device macro files like ps.tmac declare color names; you can define addi‐
tional ones with the defcolor request (see groff(7)).
To change the name of the vbox in TeX mode, set the pseudo-variable figname (which is actually a specially parsed
command) within a picture. Example:
.PS
figname = foobar;
...
.PE
The picture is then available in the box \foobar.
pic assumes that at the beginning of a picture both glyph and fill color are set to the default value.
Arrow heads will be drawn as solid triangles if the variable arrowhead is non-zero and either TeX mode is enabled or
the -n option has not been given. Initially, arrowhead has a value of 1. Solid arrow heads are always filled with
the current outline color.
The troff output of pic is device-independent. The -T option is therefore redundant. All numbers are taken to be in
inches; numbers are never interpreted to be in troff machine units.
Objects can have an aligned attribute. This will only work if the postprocessor is grops(1) or gropdf(1). Any text
associated with an object having the aligned attribute will be rotated about the center of the object so that it is
aligned in the direction from the start point to the end point of the object. This attribute will have no effect on
objects whose start and end points are coincident.
In places where nth is allowed, 'expr'th is also allowed. “'th“ is a single token: no space is allowed between the
apostrophe and the “th”. For example,
for i = 1 to 4 do {
line from 'i'th box.nw to 'i+1'th box.se
}
Conversion
To obtain a stand-alone picture from a pic file, enclose your pic code with .PS and .PE requests; roff configuration
commands may be added at the beginning of the file, but no roff text.
It is necessary to feed this file into groff without adding any page information, so you must check which .PS and .PE
requests are actually called. For example, the mm macro package adds a page number, which is very annoying. At the
moment, calling standard groff without any macro package works. Alternatively, you can define your own requests,
e.g., to do nothing:
.de PS
..
.de PE
..
groff itself does not provide direct conversion into other graphics file formats. But there are lots of possibili‐
ties if you first transform your picture into PostScript® format using the groff option -Tps. Since this ps-file
lacks BoundingBox information it is not very useful by itself, but it may be fed into other conversion programs, usu‐
ally named ps2other or pstoother or the like. Moreover, the PostScript interpreter Ghostscript (gs(1)) has built-in
graphics conversion devices that are called with the option
gs -sDEVICE=
Call
gs --help
for a list of the available devices.
An alternative may be to use the -Tpdf option to convert your picture directly into PDF format. The MediaBox of the
file produced can be controlled by passing a -P-p papersize to groff.
As the Encapsulated PostScript File Format EPS is getting more and more important, and the conversion wasn't regarded
trivial in the past you might be interested to know that there is a conversion tool named ps2eps which does the right
job. It is much better than the tool ps2epsi packaged with gs.
For bitmapped graphic formats, you should use pstopnm; the resulting (intermediate) pnm(5) file can be then converted
to virtually any graphics format using the tools of the netpbm package.
Files
/usr/share/groff/1.23.0/tmac/pic.tmac
offers simple definitions of the PS, PE, PF, and PY macros.
Bugs
Characters that are invalid as input to GNU troff (see the groff Texinfo manual or groff_char(7) for a list) are re‐
jected even in TeX mode.
The interpretation of fillval is incompatible with the pic in Tenth Edition Research Unix, which interprets 0 as
black and 1 as white.
See also
/usr/share/doc/groff-base/pic.ps.gz
“Making Pictures with GNU pic”, by Eric S. Raymond. This file, together with its source, pic.ms, is part of
the groff distribution.
“PIC—A Graphics Language for Typesetting: User Manual”, by Brian W. Kernighan, 1984 (revised 1991), AT&T Bell Labora‐
tories Computing Science Technical Report No. 116
ps2eps is available from CTAN mirrors, e.g., ftp://ftp.dante.de/tex-archive/support/ps2eps/
W. Richard Stevens, Turning PIC into HTML
W. Richard Stevens, Examples of pic Macros
troff(1), groff_out(5), tex(1), gs(1), ps2eps(1), pstopnm(1), ps2epsi(1), pnm(5)
groff 1.23.0 2 December 2025 pic(1)