3.3 Environment variables

The behavior of plot is affected by several environment variables. We have already mentioned the environment variables BITMAPSIZE, PAGESIZE, BG_COLOR, EMULATE_COLOR, MAX_LINE_LENGTH, and ROTATION. They serve as backups for the several options ‘--bitmap-size’, ‘--page-size’, ‘--bg-color’, ‘--emulate-color’, ‘--max-line-length’, and ‘--rotation’. The remaining environment variables are specific to individual output formats.

plot -T X, which pops up a window on an X Window System display and draws graphics in it, checks the DISPLAY environment variable. The value of this variable determines the display on which the window will be popped up.

plot -T png and plot -T gif, which produce output in PNG format and pseudo-GIF format respectively, are affected by two environment variables. If the value of the INTERLACE variable is "yes", the output file will be interlaced. Also, if the value of the TRANSPARENT_COLOR environment variable is the name of a color that appears in the output file, that color will be treated as transparent by most applications. For information on what color names are recognized, see Color Names.

plot -T pnm, which produces output in Portable Anymap (PBM/PGM/PPM) format, is affected by the PNM_PORTABLE environment variable. If its value is "yes", the output file will be in the portable (human readable) version of PBM, PGM, or PPM format, rather than the default (binary) version.

plot -T cgm, which produces CGM files that comply with the WebCGM profile for Web-based vector graphics, is affected by two environment variables. By default, a version 3 CGM file is generated. Many older CGM interpreters and viewers, such as the ones built into Microsoft Office and other commercial software, only support version 1 CGM files. The CGM_MAX_VERSION environment variable may be set to "1", "2", "3", or "4" (the default) to specify a maximum value for the version number. The CGM_ENCODING variable may also be set, to specify the type of encoding used in the CGM file. Supported values are "clear_text" (i.e., human readable) and "binary" (the default). The WebCGM profile requires that the binary encoding be used.

plot -T pcl, which produces PCL 5 output for Hewlett–Packard printers, is affected by the environment variable PCL_ASSIGN_COLORS. It should be set to "yes" when producing PCL 5 output for a color printer or other color device. This will ensure accurate color reproduction by giving the output device complete freedom in assigning colors, internally, to its “logical pens”. If it is "no" then the device will use a fixed set of colored pens, and will emulate other colors by shading. The default is "no" because monochrome PCL 5 devices, which are more common than colored ones, must use shading to emulate color.

plot -T hpgl, which produces Hewlett–Packard Graphics Language output, is also affected by several environment variables. The most important is HPGL_VERSION, which may be set to "1", "1.5", or "2" (the default). "1" means that the output should be generic HP-GL, "1.5" means that the output should be suitable for the HP7550A graphics plotter and the HP758x, HP7595A and HP7596A drafting plotters (HP-GL with some HP-GL/2 extensions), and "2" means that the output should be modern HP-GL/2. If the version is "1" or "1.5" then the only available fonts will be vector fonts, and all lines will be drawn with a default thickness (the ‘-W’ option will not work). Additionally, if the version is "1" then the filling of arbitrary curves with solid color will not be supported (circles and rectangles aligned with the coordinate axes may be filled, though).

The position of the plot -T hpgl graphics display on the page can be rotated 90 degrees counterclockwise by setting the HPGL_ROTATE environment variable to "yes". This is not the same as the rotation obtained with the ‘--rotation’ option, since it both rotates the graphics display and repositions its lower left corner toward another corner of the page. Besides "no" and "yes", recognized values for the HPGL_ROTATE variable are "0", "90", "180", and "270". "no" and "yes" are equivalent to "0" and "90", respectively. "180" and "270" are supported only if HPGL_VERSION is "2" (the default).

Opaque filling and the drawing of visible white lines are supported only if HPGL_VERSION is "2" (the default) and the environment variable HPGL_OPAQUE_MODE is "yes" (the default). If the value is "no" then opaque filling will not be used, and white lines (if any), which are normally drawn with pen #0, will not be drawn. This feature is to accommodate older HP-GL/2 devices. HP-GL/2 pen plotters, for example, do not support opacity or the use of pen #0 to draw visible white lines. Some older HP-GL/2 devices reportedly malfunction if asked to draw opaque objects.

By default, plot -T hpgl will draw with a fixed set of pens. Which pens are present may be specified by setting the HPGL_PENS environment variable. If HPGL_VERSION is "1", the default value of HPGL_PENS is "1=black"; if HPGL_VERSION is "1.5" or "2", the default value of HPGL_PENS is "1=black:2=red:3=green:4=yellow:5=blue:6=magenta:7=cyan". The format should be self-explanatory. By setting HPGL_PENS, you may specify a color for any pen in the range #1...#31. For information on what color names are recognized, see Color Names. Pen #1 must always be present, though it need not be black. Any pen in the range #2...#31 may be omitted.

If HPGL_VERSION is "2" then plot -T hpgl will also be affected by the environment variable HPGL_ASSIGN_COLORS. If the value of this variable is "yes", then plot -T hpgl will not be restricted to the palette specified in HPGL_PENS: it will assign colors to “logical pens” in the range #1...#31, as needed. The default value is "no" because other than color LaserJet printers and DesignJet plotters, not many HP-GL/2 devices allow the assignment of colors to logical pens. In particular, HP-GL/2 pen plotters do not.

plot -T tek, which produces output for a Tektronix terminal or emulator, checks the TERM environment variable. If the value of TERM is a string beginning with "xterm", "nxterm", or "kterm", it is taken as a sign that plot is running in an X Window System VT100 terminal emulator: an xterm, nxterm, or kterm. Before drawing graphics, plot -T tek will emit an escape sequence that causes the terminal emulator's auxiliary Tektronix window, which is normally hidden, to pop up. After the graphics are drawn, an escape sequence that returns control to the original VT100 window will be emitted. The Tektronix window will remain on the screen.

If the value of TERM is a string beginning with "kermit", "ansi.sys", or "nansi.sys", it is taken as a sign that plot is running in the VT100 terminal emulator provided by the MS-DOS version of kermit. Before drawing graphics, plot -T tek will emit an escape sequence that switches the terminal emulator to Tektronix mode. Also, some of the Tektronix control codes emitted by plot -T tek will be kermit-specific. There will be a limited amount of color support, which is not normally the case (the 16 ansi.sys colors will be supported). After drawing graphics, plot -T tek will emit an escape sequence that returns the emulator to VT100 mode. The key sequence `ALT minus' can be employed manually within kermit to switch between the two modes.