This is the official manual for the latest Org-mode release.
The value of the
prologue header argument will be prepended to the
code block body before execution. For example,
:prologue "reset" may
be used to reset a gnuplot session before execution of a particular code
block, or the following configuration may be used to do this for all gnuplot
code blocks. Also see epilogue.
(add-to-list 'org-babel-default-header-args:gnuplot '((:prologue . "reset")))