org-mode: How can noweb handle a multiple line output

Question

I have a code chunk in my document that I want to use as a list of patterns to search for with grep.

If I were just writing a script without org-babel, I could write.

a="ar
er
ir
or
ur"

printf "Four\nscore\nand\nseven\nyears\nago" | grep -F "$a"

And the results would be

Four
score
years

But instead of $a, I want to use the output of an earlier code block.

#+NAME: vowel_r
#+BEGIN_SRC sh :shebang "#!/bin/bash" :results verbatim
a="ar
er
ir
or
ur"
echo "$a"
#+END_SRC

#+RESULTS: vowel_r
: ar
: er
: ir
: or
: ur

I would have thought that this would work.

#+BEGIN_SRC sh :shebang "#!/bin/bash" :noweb yes
printf "Four\nscore\nand\nseven\nyears\nago" | grep -F "<<vowel_r()>>"
#+END_SRC

But it throws the error.

/tmp/babel-4438QgK/sh-script-4438Wst: line 8: unexpected EOF while looking for matching `"'
/tmp/babel-4438QgK/sh-script-4438Wst: line 9: syntax error: unexpected end of file

By looking at the code with C-c C-v v, it seems that noweb is treating each line of the output separately, instead of as a multi-line string.

printf "Four\nscore\nand\nseven\nyears\nago" | grep -F "ar
printf "Four\nscore\nand\nseven\nyears\nago" | grep -F "er
printf "Four\nscore\nand\nseven\nyears\nago" | grep -F "ir
printf "Four\nscore\nand\nseven\nyears\nago" | grep -F "or
printf "Four\nscore\nand\nseven\nyears\nago" | grep -F "ur
printf "Four\nscore\nand\nseven\nyears\nago" | grep -F ""

Removing the quote marks around <<vowel_r>> just leads to a grep error.

How can I get noweb to treat the output of the earlier block as a multi-line string, instead of handling each line separately?

Thank you!

Answer 1

I don't use noweb, but I've occasionally been tripped up by multi-line input or output in source-code blocks. The following might solve your problem, if a verbatim insertion of the noweb code is sufficient for you:

#+NAME: vowel_r
#+BEGIN_SRC sh
ar
er
ir
or
ur
#+END_SRC

#+BEGIN_SRC sh :shebang "#!/bin/bash" :noweb yes :results verbatim
printf "Four\nscore\nand\nseven\nyears\nago" | grep -F <<vowel_r>>
#+END_SRC

#+RESULTS:
: years
: score
: Four

I don't know why the output is in reverse order from what you get on the command line!