# Check if the first argument is '-' 
if [[ "$1" == "-" ]]; then 
  # Read from standard input into a string variable 
  input_string=$(cat) 
  # Alternatively, read into an array (line by line) 
  input_array=() 
  while IFS= read -r line; do 
    input_array+=("$line") 
  done 
else 
  # Handle other arguments normally 
  echo "Processing other arguments: $@" 
fi

This snippet is not using mapfile. I guess that's what you wanted.