1.20 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 and sprintf.
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.