Automating Repetitive Tasks in Shell with a Simple Loop Function

When working with batch processing tasks—such as encoding video files, image processing, or running a series of API calls—you often need to execute the same script multiple times, sometimes with a short delay between runs. Instead of manually running the script or writing a separate looping script each time, you can streamline the process by adding a simple function to your shell configuration.

The loop Function

This handy loop function allows you to repeatedly execute a command a specified number of times, optionally adding a delay between executions:

loop() {
  if [ "$#" -lt 2 ]; then
    echo "Usage: loop <number_of_times> [sleep_duration] <command> [args...]"
    return 1
  fi

  local count=$1
  shift

  local sleep_duration=0
  if [[ "$1" =~ ^[0-9]+([.][0-9]+)?$ ]]; then
    sleep_duration=$1
    shift
  fi

  for ((i = 1; i <= count; i++)); do
    "$@"
    if [ "$i" -lt "$count" ]; then
      sleep "$sleep_duration"
    fi
  done
}

How It Works

1. Argument Parsing:
   • The function expects at least two arguments: the number of times to repeat the command and the command itself.
   • If the second argument is a valid number, it’s treated as the sleep duration before each iteration.
2. Loop Execution:
   • The command runs the specified number of times.
   • If a sleep duration is provided, it waits between executions.

Example Use Cases

Running a Python Script on Multiple Video Files

Imagine you have a Python script that processes video files and moves on to the next one when it finishes. You can run it multiple times with a short pause between executions:

loop 5 2 python process_video.py

This will:

• Run python process_video.py 5 times.
• Pause for 2 seconds between each run.

Testing an API Endpoint

If you’re testing an API and want to make repeated requests with a delay, you can use:

loop 10 1 curl -X GET https://api.example.com/data

This sends 10 GET requests, with a 1-second pause between each.

Running Background Jobs

You can also use this function to restart a script multiple times in the background:

loop 3 5 ./restart_service.sh &

Why Use This Instead of a While Loop?

While you could write a while loop in your terminal, this function:

• Saves typing by handling looping and delays for you.
• Prevents common mistakes like infinite loops.
• Can be easily reused across multiple tasks.

Final Thoughts

By adding this loop function to your shell configuration, you create a versatile and reusable tool for automating repetitive tasks. Whether you’re processing files, making API calls, or running background jobs, this simple function can save you time and effort.

Give it a try and tweak it to fit your workflow!