A variable modified inside a while loop is not remembered

Question

In the following program, if I set the variable $foo to the value 1 inside the first if statement, it works in the sense that its value is remember

Answer 1

I use stderr to store within a loop, and read from it outside. Here var i is initially set and read inside the loop as 1.

# reading lines of content from 2 files concatenated
# inside loop: write value of var i to stderr (before iteration)
# outside: read var i from stderr, has last iterative value

f=/tmp/file1
g=/tmp/file2
i=1
cat $f $g | \
while read -r s;
do
  echo $s > /dev/null;  # some work
  echo $i > 2
  let i++
done;
read -r i < 2
echo $i

Or use the heredoc method to reduce the amount of code in a subshell. Note the iterative i value can be read outside the while loop.

i=1
while read -r s;
do
  echo $s > /dev/null
  let i++
done <