@node Environment Variables, Erase, Edit, Commands

@iftex
@syntax Environment Variables.
@end iftex
@example
Environment (`sm') Variables
@end example
@pindex Environment Variables

SM environment variables are defined in @file{.sm} files, which are searched
for along a path which typically consists of
the current directory, your home directory, and then some system place. You
can specify your own search path by setting the environment (VMS: logical)
variable @code{SMPATH}.
If ~ appears in a path it is interpreted as your home directory unless you
specified @code{-u NAME} when starting SM, in which case it will be interpreted
as NAME's home directory instead.
Alternatively, you can specify the name of the environment file using the
`-f' flag on the command line; if it starts with a @file{/} it will be taken
to be an absolute path name, otherwise it will be taken relative to the
current path.

If you invoke SM with the @code{-f} or @code{-u}
flags, the are @emph{not} passed on to raster devices, so if you plot
to a device that invokes @code{rasterise} it will use the @code{.sm} files
specified by @code{$SMPATH}.

Each line of the files is taken to consist of a variable name, and the
rest of the line which is taken to be its value. Any variable may be
accessed using the DEFINE @code{name :} command, which defines @code{name}
from the environment file.

Comments run from `#' to the end of the line.
If the first character of a line is a `@@' or `+' the name is taken to start
with the second character. A `@@' means that the entry isn't present, and
that SM should stop searching the path for it. A `+' means that SM should
keep on searching the current @file{.sm} file, and then the rest of the
search path, looking for more entries with the same name. If it finds one,
the second value is added to the end of the first (and if the second
occurrence also had a `+' specified the search continues).
@findex .sm stopping search for a variable with @@
@findex .sm concatenating values with +

Some entries in the environment file are special to SM, although
you are free to use them to your own ends as well. For most of those for
which SM is only interested in whether the variable is defined, a value
of 0 means that it shouldn't be defined. The variables are:
@table @code
@item background
The background colour for plots
@item case_fold_search
If non-zero, make searches case insensitive
@item default_font
The default font for labels
@item device
Your initial graphics device
@item edit
A file of keybindings to read (@pxref{Key Bindings}).
@item fan_compress
Apply fan compression when connecting lines. This was donated by a user, and
is intended to reduce the number of lines actually plotted to the device;
whether it is useful is not clear. The reference is
@i{IEEE Computer Graphics and Applications, March 1989,
`Faster Plots by Fan Data-Compression', by R.A. Fowell and D.D. McNeil}.

@item file_type
The type of 2-D image for the IMAGE command
@item filecap
The filecap file to use (default: same as graphcap)
@item line_up_exponents
Force an extra space before single-digit exponents in axis labels
@item fonts
The name of the binary fonts file
@item foreground
The foreground colour for plots
@item graphcap
The graphcap file to use
@item help
The help directory
@item history
The length of the history list (default: 80)
@item history_char
The character used to recall commands (default: ^)
@item history_file
File to save history in
@item macro
The default macro directory
@item macro2
Your private macro directory
@item missing_macro_continue
If defined, a reference to a missing macro isn't a syntax error
@item name
The name SM calls you by
@item noclobber
Refuse to overwrite existing files with MACRO WRITE or PRINT.
@item overload
If non-zero, overload some commands
@item printer
The default printer (see hcopy and hmacro)
@item prompt
The initial value of SM's prompt
@item prompt2
The initial value of SM's secondary prompt
@item remember_history_line
Remember which line you last reused
@item save_file
Default file to save a SM session in
@item save_read_ptr
Save the position of the read pointer between READ commands
@item temp_dir
The directory for temporary files
@item term
Default terminal, over-ruling @code{TERM}
@item termcap
The file describing terminals to SM
@item TeX_strings
Use @TeX{}-style strings for labels
@item traceback
Print the macro stack following an error
@item uppercase
Define uppercase versions of some macros
@item x_gutter
@itemx y_gutter
Modify the spacing between windows when using the WINDOW command.
(These are not actually read from the @file{.sm} by the default
startup macro, you have to set them yourself).
@end table
Under Unix, you should omit the @code{termcap} entry, or point it at
`/etc/termcap'. Also under Unix, SM knows how to look up your
name, so you can omit the @code{name} entry. If you try to use a name
with more than one word, SM will use the first so you'll have
to call yourself `my_lord' rather than `my lord' (the `_' will be
replaced by a space).

Some of these are used directly by SM (e.g. @code{help}, @code{fonts},
but some are merely used by the @code{startup} macro to set the initial
value of SM variables (e.g. @code{TeX_strings}, @code{file_type}).
Other names may be used by the default @code{startup} macro, e.g.
@code{macro2} to specify a private macro directory or
@code{term} to specify the terminal that you are using. See the
discussion of @code{startup} under `useful macros'.