Command-line substitution is specified by a system command enclosed in
backquotes. This command is spawned and the output it produces replaces
the name of the command (and backquotes) on the command line. Some
implementations also support pipes; see plot data-file special-filenames.
Newlines in the output produced by the spawned command are replaced with blanks.
Command-line substitution can be used anywhere on the gnuplot command
line.
Example:
This will run the program leastsq and replace leastsq (including
backquotes) on the command line with its output:
f(x) = leastsq
or, in VMS
f(x) = run leastsq