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`