The behavior of
plot is affected by several environment
variables. We have already mentioned the environment variables
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
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
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
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
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
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.
plot -T hpgl will draw with a fixed set of pens.
Which pens are present may be specified by setting the
environment variable. If
HPGL_VERSION is "1", the default
HPGL_PENS is "1=black"; if
"1.5" or "2", the default value of
"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.
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
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
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
is running in the VT100 terminal emulator provided by the MS-DOS version
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
-T tek will be
kermit-specific. There will be a limited amount
of color support, which is not normally the case (the 16
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.