• State "DONE" from "STARTED" 2010-08-26 Thu 17:05
• State "STARTED" from "PROPOSED" 2010-08-25 Wed 11:32
• State "PROPOSED" from "" 2010-08-15 Sun 14:06

In general if `org-confirm-babel-evaluate' is set to nil, then code blocks can be evaluated without the need for explicit confirmation and if it is set to a truthy value then explicit confirmation is required by the user for every code block evaluation.

The :eval header argument can never be used to decrease the level of confirmation required from the user, because that could result in a security risk, however it can create additional barriers to evaluation. For example the following should make you nervous if the :eval no header argument were not present.

#+begin_src sh :eval never
  sudo rm -rf /
#+end_src

The :eval header argument can take the following values.

no or never

the source block can not be evaluated, no matter what

query

the user will be queried before every evaluation regardless of the value of `org-confirm-babel-evaluate'

For backwards compatibility the :noeval header argument is an alias for :eval no.

The following demonstrates this header argument. On export the user is queried once, for the this-is-ls which is called by the final emacs-lisp code block.

*** eval and noeval
date, should export both, but won't output results because of presence
of the =:noeval= header argument.
#+begin_src sh :noeval :exports both
  date
#+end_src

should export code, so no need to do anything
#+begin_src sh
  date
#+end_src

should export nothing, and should not query
#+source: this-is-ls
#+begin_src sh :eval query :exports none
  date
#+end_src

should export results, and should trigger query above
#+begin_src emacs-lisp :var ls=this-is-ls :exports results
  ls
#+end_src

It exports to the following…