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Name | Synopsis | Description | Options | Usage | Exit status | 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 into the language understood by TeX or troff. It copies
each file's contents to the standard output stream, except for
lines between .PS and any of .PE, .PF, or .PY which it interprets
as picture descriptions. 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.
--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 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 option is
unnecessary in GNU pic because the troff it generates is
device-independent.
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. 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, 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 {
line from 'i'th box.nw to 'i+1'th box.se
}
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.
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.
/usr/local/share/groff/1.23.0/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.
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.
/usr/local/share/doc/groff-1.23.0/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)
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 project's upstream Git repository
⟨https://git.savannah.gnu.org/git/groff.git⟩ on 2025-02-02. (At
that time, the date of the most recent commit that was found in
the repository was 2025-01-28.) 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 1.23.0.2722-658f-dirty 2025-01-02 pic(1)
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HTML rendering created 2025-02-02 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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