How to select the nth char from a string for each line in a file?

Every line has a word and a number. I need somehow to select the nth letter which all together will make a new word. For example:

and 3
for 3
map 2
wrestle 1

draw

it has to start like this

cat char.txt | ...

and I’m only allowed to use sed (no awk, perl, …).

I know how to select all the numbers

sed 's/(.*) (.*)/2/g'

or the text

sed 's/(.*) (.*)/1/g'

and I was thinking about

cat char.txt | head -c $(sed 's/(.*) (.*)/2/g') | tail -c 1 | sed 's/n//g'

but it won’t work because it won’t iterate thought all the lines and for some reason it won’t even work on a single line.

Need some help and guidance pls

Ty

Answer

while read w n; do echo -n ${w:(($n-1)):1}; done < filename

Output:

draw

---

${parameter:offset:length}: 
   Substring Expansion. Expands to up to length characters of parameter
   starting at the character specified by offset.