--- name: "pic" section: "1" platform: "linux" package: "groff" version: "1.24.2-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/pic" --- # pic(1) compile pictures for troff or TeX ## 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)](/groff/1.md) document formatting system. *pic* is a [*troff*(1)](/troff/1.md) preprocessor that translates descriptions of diagrammatic pictures embedded in [*roff*(7)](/roff/7.md) 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)](/groff/1.md). 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)](/groff_out/5.md). 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)](/system/3.md). Ignored if **-U** option not specified. - **copy** **"***filename***"** Include *filename* at this point in the file. - **copy** \[**"** **copy** \[**"** *filename***"** \] **thru** *X body X* \[**until** " *word***"** \] *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)](/sprintf/3.md) 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)](/printf/3.md), 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)](/groff/7.md)). *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)](/grops/1.md) and [*gropdf*(1)](/gropdf/1.md) 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 *n***th** 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)](/pic2graph/1.md), 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)](/gs/1.md)), which exposes format converters via its **-sDEVICE=** option. “**gs --help**” lists available devices. Alternatively, produce a PDF with “**groff -T pdf**”; [*gropdf*(1)](/gropdf/1.md)'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)](/ps2epsi/1.md), and a standalone package and command [*ps2eps*(1)](/ps2eps/1.md) is also available.\ For raster image formats, use [*pstopnm*(1)](/pstopnm/1.md); the resulting [*pnm*(5)](/pnm/5.md) file can be then converted to virtually any image format using the *netpbm* tools. GNU *plotutils* offers a [*pic2plot*(1)](/pic2plot/1.md) 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 - */usr/share/groff/1.24.2/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)](/groff_char/7.md) 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 - */usr/share/doc/groff-1.24.2/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)](/troff/1.md), [*groff\_out*(5)](/groff_out/5.md), [*tex*(1)](/tex/1.md), [*gs*(1)](/gs/1.md), [*ps2eps*(1)](/ps2eps/1.md), [*pstopnm*(1)](/pstopnm/1.md), [*ps2epsi*(1)](/ps2epsi/1.md), [*pnm*(5)](/pnm/5.md)