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
into the language understood by TeX or troff. It copies each file's
contents to the standard output stream, translating each picture
between lines starting with .PS and any of .PE, .PF, or .PY. 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. Normally, pic is
not executed directly by the user, but invoked by specifying the -p
option to groff(1). If no file operands are present, or if file is
"-", pic reads the standard input stream.
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 horizontally 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 \. GNU pic
gives a line beginning with .ps special treatment: it takes an
optional integer argument specifying the line thickness (pen
size) in milliinches, a missing argument restores the previous
line thickness, and 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 Enable safer mode and ignore any subsequent -U option. In safer
mode, pic ignores sh commands, which can be useful when
operating on untrustworthy input. pic operates in safer mode by
default.
-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 option is
unnecessary in GNU pic because the troff it generates is
device-independent.
Usage
This section primarily discusses the differences between GNU pic and
the Eighth Edition 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 version 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 unaltered except for a %
suffix to avoid unwanted spaces. Use this feature to change fonts or
the value of \baselineskip. Other applications may produce 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 defines 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 produces slightly more vertical 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 example), 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 supported. 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. GNU pic recognizes double-quoted strings within delimiters
of either kind; such strings 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. expr3 can be
negative, in which case variable is then tested whether it is
greater than or equal to expr2. A * prefix on variable
multiplies it by expr3 (which must be greater than zero) at each
iteration rather than incrementing it. If the range constraint
on expr3 isn't met, the loop does not execute. X can be any
character not 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 in if-true. Y can be any
character not in if-false.
print arg ...
Catenate and write arguments to the standard error stream
followed by a newline. Each arg must be an expression, a
position, or text. This feature is useful for debugging.
command arg ...
Catenate 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. Thus,
.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 via system(3). Ignored if -U option not
specified.
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 occurrences 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, GNU
pic reads lines only until encountering one beginning with word;
which it then discards. X can be any character not 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 predefined
variables to their default values. Variable names may be
separated by commas, spaces, or both. Assigning a value to
scale also causes all predefined variables that control
dimensions to be reset to their default values times the new
value of scale.
plot expr ["text"]
Create a text object by using text as a format string for
sprintf(3) with an argument of expr. If text is omitted, "%g"
is implied. Attributes can be specified in the same way as for
a normal text object. Caution: be very careful that you specify
an appropriate format string in text; pic's validation of it is
limited. plot is deprecated in favour of sprintf.
var := expr
Update an existing variable. var must already be defined, and
expr is assigned to var without creating a variable local to the
current block. (By contrast, = defines var in the current block
if it is not already defined there, and then changes the value
in the current block only.) For example,
.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 direction. For
example, "line 2i" draws a line 2 inches long in the current direction.
The `i' (or `I') character is ignored; to use another measurement 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, respectively.
Scientific notation is allowed for numbers, as with "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 nested. For
example,
[A: [B: [C: box ]]] with .A.B.C.sw at 1,2
circle at last [].A.B.C
is acceptable.
Arcs 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 as well.
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, generalizing them from rectangles to
parallelograms. The xslanted and yslanted attributes specify the x and
y offsets of the box's upper right corner from its default position.
The .PS line accepts a second argument specifying a maximum height for
the picture. If a width of zero is specified, it is ignored when
computing the scaling factor for the picture. GNU pic always scales a
picture by the same amount vertically and horizontally. This differs
from DWB 2.0 pic, which may change the picture's aspect ratio if a
height is specified.
Each text object has an associated invisible box that determines its
compass points and implicit motion. The dimensions of the box are
taken from its width and height attributes. If the width attribute is
not supplied, the value of textwid is assumed. If the height attribute
is not supplied, the height defaults to the number of text strings
associated with the object times textht. Initially, textwid and textht
have values of 0.
In (almost all) places where a quoted text string can be used, an
expression of the form
sprintf("format", arg, ...)
can be used instead; it transforms its arguments per format, which
should be a string as described in printf(3), and appropriate to the
quantity of arguments supplied. GNU pic supports only the conversion
specifiers e, E, f, g, G, and %, modifiers "#", "-", "+", and " "
[space]), a minimum field width, and an optional precision.
The thickness of the lines used to draw objects is controlled by the
linethick variable, which is measured in points. A negative value
indicates the default thickness. In TeX output mode when the -c option
is not given, this means 8 milliinches. In troff and TeX -c output
modes, the default thickness corresponds to the type size. (Thus, if
the type size is 10 points, a line is 10 points thick.) A linethick
value of zero draws the thinnest possible line supported by the output
device. Initially, linethick has a value of -1. A thick[ness]
attribute is also available. For example, "circle thickness 1.5" draws
a circle with a line 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],
which takes an optional expression argument with a value between 0 and
1; 0 fills it with white, 1 with black, and values in between with a
proportionally gray shade. A value greater than 1 is interpreted as
the shade of gray that is being used for text and lines. Normally this
is black, but output devices may provide a mechanism for changing this.
Without an argument, the value of the variable fillval is used.
Initially, fillval has a value of 0.5. The invisible attribute does
not affect the filling of objects. Text associated with a filled
object is added after the object is filled, so that the text is not
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 additional ones with the
defcolor request (see groff(7)). pic assumes at the beginning of each
picture that the stroke and fill colors are set to the device defaults.
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. For example,
.PS
figname = foobar;
circle "dig here";
.PE
makes the picture available in the box \foobar.
Arrow heads are drawn as solid triangles if the variable arrowhead is
non-zero and either TeX mode is enabled or the -n option is not used.
Initially, arrowhead has a value of 1. Solid arrow heads are always
filled with the current outline (stroke) color.
The troff output of pic is device-independent. The -T option is
therefore redundant. Except where noted, all measurements and
dimensions use inches implicitly; they are never interpreted as troff
basic units.
Objects can have an aligned attribute, but it is supported only by the
grops(1) and gropdf(1) output drivers. Any text associated with an
aligned object is rotated about the object's center such that it is
oriented along a line connecting the start and end points of the
object. aligned has 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".
Consider the following example.
for i = 1 to 4 do {
box
move right 0.5
}
for i = 1 to 3 do {
arrow from `i'th box.ne to `i+1'th box.sw
}
Arbitrary polygons can be drawn using the polygon keyword followed by a
series of n-1 line segments, where n is the number of edges of the
polygon. This allows GNU troff to interpret the line segments as a
complete object such that the filled and shaded attributes may be used.
The last user-specified line segment determines the polygon's final
drawing position and direction. For example, draw and fill a triangle
with the following.
polygon up 1 then right 1 down 0.5 fill 0.5
Two reference point suffixes permit the positioning of drawing elements
relative to a polygon. ".vertex expr" locates the vertices, and
".midpoint expr" for locating the midpoints of edges. GNU pic numbers
vertices and midpoints in drawing order starting from 1 . You can
abbreviate .vertex as .v or .ver, and .midpoint as .mid.
For example,
arrow down
polygon up 0.5 right 1 \
then down 0.5 right 1 \
then down 0.5 left 1 \
with .v2 at last line.end
arrow down from last polygon.v4
creates and correctly places a flowchart decision diamond.
.center (.c) is also available, but compass points do not work as
expected and should not be used with polygons.
Converting pic to other image formats
To create a stand-alone graphics file from a pic file, first compose
the picture. Bracket your pic code with .PS and .PE tokens. groff
requests that don't produce formatted output may precede .PS, but
format no text, not even any injected by a macro package, which may
include a page number even on the first page, as mm does by default.
Consider writing a "raw" roff document that uses no macro package.
Next, convert the roff/pic input into the desired format. groff
distributes a simple utility, pic2graph(1), for this purpose. Other
possibilities exist, particularly if you first transform your picture
into PostScript format with "groff -T ps". However, such a PostScript
file lacks bounding box information; roff formatters produce page-sized
output. Several tools with names beginning "psto" or "ps2" exist that
can infer the bounding box and perform a format conversion. One of
these is the PostScript interpreter Ghostscript (gs(1)), which exposes
format converters via its -sDEVICE= option. "gs --help" lists
available devices.
Alternatively, produce a PDF with "groff -T pdf"; gropdf(1)'s -p option
sets the MediaBox of the file.
The Encapsulated PostScript File (EPS) format is still sometimes seen.
The aforementioned Ghostscript offers ps2epsi(1), and a standalone
package and command ps2eps(1) is also available.
For raster image formats, use pstopnm(1); the resulting pnm(5) file can
be then converted to virtually any image format using the netpbm tools.
GNU plotutils offers a pic2plot(1) utility for converting pic input to
a wide variety of other image formats, including SVG.
Exit status
pic 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/tmac/pic.tmac
offers simple definitions of the PS, PE, PF, and PY macros.
Load it with the mso request when eschewing a full-service macro
package, or using one that doesn't supply its own definitions
for them.
Caveats
The spacing of dots and dashes in broken lines scales with other
graphics, and is configurable. For example,
line from 0,0 to 100,0 dotted 5
spaces the dots in a dotted line 5 units apart. The spacing of dashes
can be set the same way. The dashwid variable sets the length of
dashes.
Bugs
Characters that are invalid as input to GNU troff (see the groff
Texinfo manual or groff_char(7) for a list) are rejected even in TeX
mode.
Research Tenth Edition Unix pic's fillval interprets 0 as black and 1
as white, incompatibly with GNU pic.
See also
/opt/local/share/doc/groff-1.24.1/pic.ps
"Making Pictures with GNU pic", by Eric S. Raymond <esr@thyrsus
.com>. 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 Laboratories 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 <http://www.kohala.com/start/
troff/pic2html.html>
W. Richard Stevens, Examples of pic Macros <http://www.kohala.com/
start/troff/pic.examples.ps>
troff(1), groff_out(5), tex(1), gs(1), ps2eps(1), pstopnm(1),
ps2epsi(1), pnm(5)
groff 1.24.1 2026-05-15 pic(1)
groff 1.24.1 - Generated Mon May 18 13:14:47 CDT 2026