How to pass newline ("\n") string to noweb <<call>>

Question

Trying to pass multiline argument to Org code block. If make direct call of block then it's Ok. But when call it through noweb ref then Error raised

#+NAME: pr
#+BEGIN_SRC elisp :results value :var n="a\nb\nc"
"%p" n
#+END_SRC

#+RESULTS: pr
: a
: b
: c


#+BEGIN_SRC elisp :noweb yes :results value
<<pr("a\nb\nc")>>
#+END_SRC

eval: Symbol’s value as variable is void: a

I need this to be able to use pr block with another noweb call already in SQL like this

insert into table
select @SPID, <<pr("1\n2\n3\n4")>>

proposing to get string executed in sqlcmd

select @SPID, 1
select @SPID, 2
select @SPID, 3
select @SPID, 4

Answer 1

I understand your confusion.

The good news is that your code is already passing new lines correctly into your noweb call.

The reason you're seeing the eval: Symbol’s value as variable is void: a error is because of the generated elisp code.

If you execute the following code you'll see the same error message:

#+BEGIN_src elisp
a
b
c
#+END_src 

A convenient way to preview how code will be rendered by noweb is to put cursor inside you block and press C-c C-v v.

Another way to preview code is to render the code in multiple steps:

#+NAME: sql-stmt
#+BEGIN_SRC sql :noweb yes :eval never
  insert into table
  select @SPID, <<pr("1\n2\n3\n4")>>
#+END_SRC   

#+BEGIN_SRC css :noweb yes :wrap "src sql"
  <<sql-stmt>>
#+END_SRC

#+RESULTS:
#+BEGIN_src sql
insert into table
select @SPID, 1
select @SPID, 2
select @SPID, 3
select @SPID, 4
#+END_src 

Note You should be cautious when generating SQL statements this way because it is very easy to accidentally introduce a SQL injection vulnerability into your source code. Be sure to verify your data and sql statements before executing against your database.

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This code was tested using:
GNU Emacs 25.3.1 (x86_64-apple-darwin16.7.0, NS appkit-1504.83 Version 10.12.6 (Build 16G29))
org-mode version: 9.1.2