iterating through each line and each character in a file - bash

Question

i'm trying to get a file name, and a character index, and to print me the characters with that index from each line (and do it for each character index the user enters if such character exists).
This is my code:
#!/bin/bash
read file_name
while read x
do
if [ -f $file_name ]
then
while read string
do
counter=0
while read -n char
do
if [ $counter -eq $x ]
then
echo $char
fi
counter=$[$counter+1]
done < $(echo -n "$string")
done < $file_name
fi
done
But, it says an error:
line 20: abcdefgh: No such file or directory
line 20 is the last done, so it doesn't help me figure out where is the error.
So what's wrong in my code and how do I fix it?
Thanks a lot.

Answer 1

I think "cut" might fit the bill:
read file_name
if [ -f $file_name ]
then
while read -n char
do
cut -c $char $file_name
done
fi

Answer 2

This line seems to be problematic:
done < $(echo -n "$string")
Replace that with:
done < <(echo -n "$string")

Answer 3

replace
counter=0
while read -n char
do
if [ $counter -eq $x ]
then
echo $char
fi
counter=$[$counter+1]
done < $(echo -n "$string")
with
if [ $x -lt ${#string} ]
then
echo ${line:$x:1}
fi
It does the same, but allows to avoid such errors.
Another approach is using cut
cut -b $(($x+1)) $file_name | grep -v "^$"
It can replace two inner loops