org-babel-exp-code-template

org-babel-exp-code-template is a variable defined in `ob-exp.el'.
Its value is

"#+BEGIN_SRC %lang%switches%flags
%body
#+END_SRC"

Documentation:
Template used to export the body of code blocks.
This template may be customized to include additional information
such as the code block name, or the values of particular header
arguments. The template is filled out using `org-fill-template',
and the following %keys may be used.

lang ------ the language of the code block
name ------ the name of the code block
body ------ the body of the code block
switches -- the switches associated to the code block
flags ----- the flags passed to the code block

In addition to the keys mentioned above, every header argument
defined for the code block may be used as a key and will be
replaced with its value.

You can customize this variable.