Command-line substitution can be used anywhere on the gnuplot command line, except inside strings delimited by single quotes.
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`
These will generate labels with the current time and userid:
set label "generated on `date +%Y-%m-%d` by `whoami`" at 1,1 set timestamp "generated on %Y-%m-%d by `whoami`"