Environment: linux shell or better, ash shell in busybox (example system: Openwrt).

Given a string variable with large text "${a}" constructed in this way:

for index in $(seq 1 40000); do #it is 40000 for a reason, it helps if you want to reproduce the error on your system.
   a="${a}""\n""word ${index}"
done

and given the fact that trying to use this variable as argument for common command produce an error, for example:

echo "${a}" #fails
awk -v VAR_A="${a}" '<program>' #fails

(the failures are due: http://www.in-ulm.de/~mascheck/various/argmax/ )

How do you write such a variable to a text file, possibly using only simple commands and not sed/awk/perl/other powerful interpreter.

Ideally the text file should look like:

word 1
word 2
word 3
...

and not like:

word 1\nword 2\nword 3\n...

Update1: Someone asks "Why you cannot change the script that produce the variable $a?". Because i cannot due to, let's say, lack of authorization ("the script was working until today, so you can fix only the printing part"). So $a and its format is given, i can only find a way to print it to a file.

Update2: Using the suggested "here docs" solve most of the problems but still i have the content printed in one line. Maybe is my config?