redirect log messages to stderr

#!/bin/bash

# Function to perform an action, return a value, and log messages
my_function() {
  local input_value="$1"
  local result_value=$((input_value * 2))

  # Emit log messages to stderr
  echo "INFO: Processing input: $input_value" >&2
  echo "DEBUG: Intermediate calculation: $result_value" >&2

  # Echo the return value to stdout
  echo "$result_value"
}

# Call the function using command substitution to capture the return value
returned_value=$(my_function 5)

# Log messages from the main script
echo "INFO: Function returned: $returned_value"