Create a Command-Line Progress Spinner in Bash

#!/bin/bash

SPINNER_PID=""

# Function to display a spinning cursor
function start_spinner {
  local pid=$!
  local delay=0.1
  local spin_chars=("-" "\" " "|" "/")
  
  trap "stop_spinner" SIGINT # Catch Ctrl+C to stop spinner cleanly

  while kill -0 "$pid" 2>/dev/null; do
    for char in "${spin_chars[@]}"; do
      printf "\r%s %s" "Processing..." "$char"
      sleep "$delay"
    done
  done
  printf "\r%s
" "Processing... Done!"
}

# Function to stop the spinner and clean up
function stop_spinner {
  if [ -n "$SPINNER_PID" ]; then
    kill "$SPINNER_PID" 2>/dev/null
    wait "$SPINNER_PID" 2>/dev/null # Wait for the spinner to actually exit
  fi
  printf "\r%s
" "Operation interrupted!" # Or just clear line
  exit 1
}

# Main script logic

# --- Example: Simulate a long-running task ---
(sleep 7; echo "Task finished in background.") &
TASK_PID=$!

# Start the spinner in the background, passing the task's PID to it
start_spinner "$TASK_PID" &
SPINNER_PID=$!

# Wait for the actual task to complete
wait "$TASK_PID"

# Stop the spinner (if it's still running for some reason, though `start_spinner` should self-terminate)
if kill -0 "$SPINNER_PID" 2>/dev/null; then
  kill "$SPINNER_PID"
  wait "$SPINNER_PID" 2>/dev/null
fi

echo "
Script execution completed successfully."