[Orgmode] [babel] How to kill two birds with one stone?

[Sébastien Vauban]

#+TITLE:     Document a shell script as separate blocks
#+DATE:      2011-02-04
#+LANGUAGE:  en_US

* Abstract

When writing shell scripts, I'd like to kill *two* birds with one Babel stone:

- Be able to *execute the script in situ*, so that I get a copy of the results
  stored in (and "versioned" with) my documentation.

- Be able to *chain the code blocks*, so that I tangle a "natural" script into
  a file for later execution.

I guess I currently miss some points in order to reach that goal in a clean
way. Could you give me advice on how to get a step further down the route?

* Sample code

For the sake of clarity, let's take a simple problem: I'd like to generate a
DOT graph of links between all files from a directory tree.

The procedure:

1. (Recursively) list all files inside the directory.

2. For each file, (recursively) search for its name referenced in all the
   files.

3. Generate a DOT representation of the link between files.

** List all files under current directory

#+srcname: dw-file-tree
#+begin_src sh :results output
cd ~/Some-Project-Dir
find . -type f -print | grep -v .svn | head -n 5
#+end_src

#+results: dw-file-tree
#+begin_example
./.cvsignore
./charge_dim
./charge_fct
./compte
./controle_config
#+end_example

Here, I voluntary limit the number of results to the first 5 files, for the
compactness of this example. This sample does not include any file from
subdirectories, but it doesn't matter.

** Search recursively for anything about a file

Search through all files (ignoring =.svn= directories) for any reference to
filename given as parameter.

#+srcname: search-files-pointing-to-this-file
#+begin_src sh :results output :var f="charge_dim"
cd ~/Some-Project-Dir
find . -not \( -name .svn -prune \) -type f -print0 |\
xargs -0 grep -i --files-with-matches "$f"
#+end_src

#+results: search-files-pointing-to-this-file
#+begin_example
./.cvsignore
./charge_dim
./compte
./IFP/Chrg_dim
./IFP/Chrg_dim.avant_simple_recovery_mode_2008_03_12
./principal.env
./29Aalst/Chrg_dim
./29Aalst/Chrg_dim_interactif
./29Aalst/Publ_dim_interactif
#+end_example

HERE, I'M GIVING A FILENAME AS DEFAULT VALUE OF =f= IN ORDER TO SEE A SAMPLE
RESULTS.

** Convert to a DOT representation

For every file pointing to the file given in parameter, generate an "arrow"
(edge) in DOT representation.

#+srcname: dot-arrow-from-files-pointing-to-this-file
#+begin_src sh :results output :var f="charge_dim" :var 
data=search-files-pointing-to-this-file
for i in $(echo "$data"); do echo "    $(basename $i) -> $f"; done
#+end_src

#+results: dot-arrow-from-files-pointing-to-this-file
#+begin_example
    .cvsignore -> charge_dim
    charge_dim -> charge_dim
    compte -> charge_dim
    Chrg_dim -> charge_dim
    Chrg_dim.avant_simple_recovery_mode_2008_03_12 -> charge_dim
    principal.env -> charge_dim
    Chrg_dim -> charge_dim
    Chrg_dim_interactif -> charge_dim
    Publ_dim_interactif -> charge_dim
#+end_example

HERE, I'M WORKING GIVING ONCE AGAIN THE SAME DEFAULT VALUE FOR TESTING (AND
DOCUMENTATION) PURPOSE.

* Problem

All of the above nicely answer my first goal ("Be able to execute the script
in situ, so that I get a copy of the results stored in my documentation").

It does not allow for the second one: *how to chain the calls together*?

For example, just for chaining steps 2 and 3 (the easier to chain, I think),
I'd like to be able to write something like this:

#+srcname: search-links-and-generate-dot-arrow
#+begin_src sh :results output :var f="charge_dim" :var 
data=search-files-pointing-to-this-file :noweb yes
for i in (
    <<search-files-pointing-to-this-file>>);
do echo "    $(basename $i) -> $f"; done
#+end_src

#+results: search-links-and-generate-dot-arrow

But it yields an error:

#+begin_src text :eval no
sh: line 14: syntax error near unexpected token `('
sh: line 14: `for i in ('
#+end_src

Note, in the latter code block, that I did not even tried to really chain
steps 2 and 3: I'm rewriting step 3, including step 2 inside it.

*I certainly miss a smarter way* to achieve the above.

Quite important as well, is that the tangled file seems natural to read (for
someone that would not read it from the Org file). This means we would have to
minimize the use of "echo" and "tee" commands, among others -- but that's a
nice to have.

Do you see my point?

Do you have ideas on how to go that way?

Best regards,
  Seb

-- 
Sébastien Vauban