[sh] csv string count

#!/bin/bash

input=$1
output=$2

rm $output

n=0
while read line; do
  comma="${line//[^,]}"
  cnt="${#comma}"

  echo "Line No. ${n} : ${cnt}" >> $output

  n=$((n+1))
done < ${input}

var="text,text,text,text"
res="${var//[^,]}"
echo "$res"
echo "${#res}"

,,,
3

https://stackoverflow.com/questions/16679369/count-occurrences-of-a-char-in-a-string-using-bash

Count occurrences of a char in a string using Bash

https://linuxhint.com/read_file_line_by_line_bash/

How to read file line by line in Bash script