gnuplot documentation

36 19 gnuplot STRING 4.3 CONSTANTS AND STRING VARIABLES
for information about the requisite file structure for 3D data values; and set contour (p. 94) and set
cntrparam (p. 92) for information about contours.
In splot, control over the scales and labels of the axes are the same as with plot, except that commands
and options controlling the x2 and y2 axes have no effect whereas of course those controlling the z axis
do take effect.
18 Start-up
When gnuplot is run, it looks for an initialization file to load. This file is called .gnuplot on Unix and
AmigaOS systems, and GNUPLOT.INI on other systems. If this file is not found in the current directory,
the program will look for it in the HOME directory (under AmigaOS, Atari(single)TOS, MS-DOS,
Windows and OS/2, the environment variable GNUPLOT should contain the name of this directory;
on Windows NT, it will use USERPROFILE if GNUPLOT isn’t defined). Note: if NOCWDRC is
defined during the installation, gnuplot will not read from the current directory.
If the initialization file is found, gnuplot executes the commands in it. These may be any legal gnuplot
commands, but typically they are limited to setting the terminal and defining frequently-used functions
or variables.
19 String constants and string variables
In addition to string constants, most gnuplot commands also accept a string variable, a string expression,
or a function that returns a string. For example, the following four methods of creating a plot all result
in the same plot title:
four = "4"
graph4 = "Title for plot #4"
graph(n) = sprintf("Title for plot #%d",n)
plot ’data.4’ title "Title for plot #4"
plot ’data.4’ title graph4
plot ’data.4’ title "Title for plot #".four
plot ’data.4’ title graph(4)
Since integers are promoted to strings when operated on by the string concatenation operator, the
following method also works:
N = 4
plot ’data.’.N title "Title for plot #".N
In general, elements on the command line will only be evaluated as possible string variables if they are
not otherwise recognizable as part of the normal gnuplot syntax. So the following sequence of commands
is legal, although probably should be avoided so as not to cause confusion:
plot = "my_datafile.dat"
title = "My Title"
plot plot title title
There are three binary operators that require string operands: the string concatenation operator ".",
the string equality operator "eq" and the string inequality operator "ne". The following example will
print TRUE.
if ("A"."B" eq "AB") print "TRUE"
See also the two string formatting functions gprintf (p. 101) and sprintf (p. 27).
Substrings can be specified by appending a range specifier to any string, string variable, or string-valued
function. The range specifier has the form [begin:end], where begin is the index of the first character of
the substring and end is the index of the last character of the substring. The first character has index
1. The begin or end fields may be empty, or contain ’*’, to indicate the true start or end of the original
string. E.g. str[:] and str[*:*] both describe the full string str.