Re: Tangling flow control

["Charles C. Berry" <ccberry@ucsd.edu>]

On Tue, 8 Nov 2016, Philip Hudson wrote:

[snip]
>
> How do you do "looping" flow control?
>
> For context, what I'm trying to write is a single Org file from which
> I can tangle out a number of =~/.ssh/config= files, one for each of
> several hosts on a LAN. Within this file I need to repeatedly place a
> template =BEGIN_SRC ssh-config= block, each time with a few words and
> numbers changed. Do you do this anywhere? If so, how have you
> implemented it?
>


It sounds like what you want is a template for the src block and another 
src block that does substitutions in that template using a table of 
values inside a loop.

Just to get you started, with this template:

#+NAME: template
#+BEGIN_SRC org
   ,#+BEGIN_SRC shell :tangle %to-file
   ls -lt %filename
   ,#+END_SRC
#+END_SRC

and this helper src-block

#+NAME: get-body
#+BEGIN_SRC emacs-lisp :var src-block-name="c-code"
   (save-excursion
     (org-babel-goto-named-src-block
      src-block-name)
     (cadr (org-babel-get-src-block-info)))

#+END_SRC


running

#+header: :wrap src org :var tmpl=get-body("template")
#+BEGIN_SRC emacs-lisp
   (org-fill-template tmpl
     '(("to-file" . "abc.sh")("filename" . "my-dir")))
#+END_SRC

yields

#+RESULTS:
#+BEGIN_src org
,#+BEGIN_SRC shell :tangle abc.sh
ls -lt my-dir
,#+END_SRC
#+END_src


To revise this for your application, you need to provide a table of the 
associated values for the "to-file" and "filename" keys in the alist, read 
that table using a :var header, loop thru the table reconstructing the 
alist each time creating src blocks, and send the output to an org 
tempfile.  Then you tangle the tempfile.

Alternatively, you simply write the script files directly without 
bothering to write to an org tempfile.

HTH,

Chuck