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cron's missing brain. Stateful, time-based scripting.

Project description

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Scriptter is a brain for your cron job. You write a script (using a special YAML format), specifying a sequence of commands to run and a human-readable delay between each group of commands. Then, run Scriptter against your script every minute (or as often as you can). Scriptter will make sure that your commands are run in the sequence and timing you specified.

Uses:

I conceived of Scriptter as a way to author Twitter bots, especially Twitter bots that converse with each other. But there’s no limitation to Twitter: anything you can do in the shell, you can do in Scriptter.

Example:

Here’s a simple script to run a daily conversation between two Twitter accounts, using the t Twitter CLI:

defaults:
  delay: 1min
  activate: t set active
  update: t update
  cmd:
  - '{activate} {as}'
  - '{update} "{say}"'
  timezone: US/Eastern
---
as: Costello
say: "@Abbott I'm not... stay out of the infield! I want to know what's the guy's name in left field?"
---
as: Abbott
say: "@Costello No, What is on second."
---
as: Costello
say: "@Abbott I'm not asking you who's on second."
---
as: Abbott
say: "@Costello Who's on first!"
---
as: Costello
say: "@Abbott I don't know."
---
cmd:
- '{activate} Abbott'
- '{update} "@Costello Third base!"'
- '{activate} Costello'
- '{update} "@Abbott Third base!"'
---
delay: 10min
as: Costello
say: '@Abbott Look, you gotta outfield?'

Classic, I know. Here’s what’s going on: every time Scriptter runs, it remembers where it left off at, and at what time the next item should run. When that time comes, it looks at the cmd member. If a member isn’t present on the item, it looks in the defaults. cmd can be a single string, or a list of strings. Command strings can be templates containing formatting instructions.

Templating

The context for a command template comes from the item itself, filled in with any global defaults from the document. That’s how we can just define activate and update at the top and use them willy-nilly in command strings later. The Twitter account to use (as) and the content of the tweet (say) are defined in each item.

Time Delay

They say that comedy is all about… TIMING! So how do we control the timing of our comedic commands? The delay attribute is a human-readable time span or delay, like “5 minutes” or “5mins” or “tomorrow at 8am”, relative to the previous item. We set a default delay at the top (or if we don’t set a default, the default is, by default, 5mins).

The delay of the first item is special: that determines how long after the first invocation the script will begin. This might be useful for a script that is keyed to time of day–you could say tomorrow at 8am and the script would begin in the morning, next day after you start your cron job.

Repeating a Script

Some scripts should only run once, some should repeat forever. By default, your script will repeat (go back to the beginning) after it completes. To change this behavior, include this at the top of your script:

defaults:
    repeat: false

Command Line

You’ll usually be interacting with Scriptter via the command line:

$ scriptter --help

Normal Run

To actually run the schedule, perform commands, and change state:

$ scriptter run schedule.yaml

Trial Run

To do a trial run and find out what Scriptter will do in a given state:

$ scriptter trial schedule.yaml

This will do a dry run of the schedule, with the current state, but stop short of actually performing any actions or changing the state.

Checking Delays

If you need to get a feel for how an item list will play out in time, use the check command:

$ scriptter check schedule.yaml

This will first verify that the complete schedule is valid, well-formed, and renderable. It will go through and simulate each item in sequence, reporting when that item would run and what commands would be performed.

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