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Name | Synopsis | Description | Options | Usage | Conversion | Files | Bugs | See also | COLOPHON |
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pic(1) General Commands Manual pic(1)
pic - compile pictures for troff or TeX
pic [-CnSU] [file ...]
pic -t [-cCSUz] [file ...]
pic --help
pic -v
pic --version
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 understood 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.
Normally, 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.
--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 special
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.
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 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 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 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 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 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. 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
expression, 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
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, 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
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"]
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 limited
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 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
means draw 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.
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 parallelogram. The
xslanted and yslanted attributes specify the x and y offset of the
box's upper right corner from its default position.
The .PS line can have a second argument specifying a maximum
height for the picture. If the width of zero is specified 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 associated 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 described 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]
attribute. 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 additional 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
}
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 possibilities 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, usually 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=<devname>
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.
/usr/local/share/groff/1.23.0/tmac/pic.tmac
offers simple definitions of the PS, PE, PF, and PY macros.
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.
The interpretation of fillval is incompatible with the pic in
Tenth Edition Research Unix, which interprets 0 as black and 1 as
white.
/usr/local/share/doc/groff-1.23.0/pic.ps
“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 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)
This page is part of the groff (GNU troff) project. Information
about the project can be found at
⟨http://www.gnu.org/software/groff/⟩. If you have a bug report for
this manual page, see ⟨http://www.gnu.org/software/groff/⟩. This
page was obtained from the tarball groff-1.23.0.tar.gz fetched
from ⟨https://ftp.gnu.org/gnu/groff/⟩ on 2026-01-16. If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for the
page, or you have corrections or improvements to the information
in this COLOPHON (which is not part of the original manual page),
send a mail to man-pages@man7.org
groff 1.23.0 2 July 2023 pic(1)
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HTML rendering created 2026-01-16 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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