Re: Chaining strings between babel blocks: why so many '\'?

[Alan Schmitt <alan.schmitt@polytechnique.org>]

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Hello Nicolas,

Nicolas Goaziou <n.goaziou@gmail.com> writes:

> Hello,
>
> Alan Schmitt <alan.schmitt@polytechnique.org> writes:
>
>> I've been playing with block chaining to generate some dot file then to
>> export then as images. I had a little trouble finding the number of '\'
>> I need to put in front of a quote if I want the quote to be quoted. Here
>> is a way to make it work:
>>
>> #+name: foo
>> #+begin_src emacs-lisp :exports none
>> "bar [label = \"\\\\\"test1\\\\\"\"]\nbaz [label = \"\\\\\"test2\\\\\"\"]"
>> #+end_src
>>
>> #+results: foo
>> : bar [label = "\\"test1\\""]
>> : baz [label = "\\"test2\\""]
>>
>> #+begin_src dot :file ~/tmp/test-dot.png :var input=foo :exports results
>> graph {
>>   $input
>> }
>> #+end_src
>>
>> My question is: why can't I simply use this:
>>
>> #+name: foo
>> #+begin_src emacs-lisp :exports none
>> "bar [label = \"\\\"test1\\\"\"]\nbaz [label = \"\\\"test2\\\"\"]"
>> #+end_src
>>
>> #+results: foo
>> : bar [label = "\"test1\""]
>> : baz [label = "\"test2\""]
>>
>> (I guess the answer is in the error in replace-regexp-in-string:
>> (error "Invalid use of `\\' in replacement text")
>> .)
>
> Indeed. This function, unless told not to, treats backslashes characters
> specially.
>
>> Would it be problematic to first transform every "\\" into a "\\\\" in
>> org-babel-expand-body:dot, before the call to
>> replace-regexp-in-string?
>
> I think `replace-regexp-in-string' should be called with a non-nil
> LITERAL argument in this case.

Yes. I think it should also not try to mach the case (i.e., FIXEDCASE
should be non-nil). Here is a patch to do that.


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From c6437e8b7132d95ca432b0690bf65ede6e248567 Mon Sep 17 00:00:00 2001
From: Alan Schmitt <alan.schmitt@polytechnique.org>
Date: Thu, 27 Mar 2014 13:35:31 +0100
Subject: [PATCH] ob-dot.el: Substitute variables literally

* lisp/ob-dot.el (org-babel-expand-body:dot): Do not change the case
nor interpret '\' when substituting block variables.
---
 lisp/ob-dot.el | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lisp/ob-dot.el b/lisp/ob-dot.el
index b35d7bb..1e399e7 100644
--- a/lisp/ob-dot.el
+++ b/lisp/ob-dot.el
@@ -55,7 +55,9 @@
 	       (replace-regexp-in-string
 		(concat "\$" (regexp-quote name))
 		(if (stringp value) value (format "%S" value))
-		body))))
+		body
+		t
+		t))))
      vars)
     body))
 
-- 
1.8.5.3


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Best,

Alan