From Aegisub Manual
The name Automation covers the entire scripting functionality of Aegisub.
 About Automation
The single purpose of Automation is — as the name implies — to automate various aspects of subtitle creation and editing. To date this has mainly been for creating karaoke effects but Aegisub 2 introduces Automation 4 which also allows creating more general purpose macros and also changing the style definitions and other meta data for the subtitles.
Some of the goals of Automation:
- Macros to automate complex subtitle editing tasks
- Export filters to generate complex effects from simpler input
- Karaoke effects
- Translation note boxes
- Probably several yet-undiscovered uses
 Using Automation
Aegisub comes with several Automation scripts already packaged and ready to use. This includes the advanced Karaoke Templater script (which covers everything simple-k-replacer, line-per-syllable and multi-template did in Automation 3) and a collection of macros to simplify some editing tasks.
Aegisub almost always has several Automation scripts loaded at a time. You can see what scripts are loaded, and load/unload more from the Automation Manager window.
All Automation scripts also present themselves in Aegisub in one way or another. Some appear as macros in the Automation menu and others appear as filters in the Export dialog. Some scripts even appear in both places.
 Automation for programmers
There is several example scripts included with Aegisub to give you a head start on writing your own ones. A word of warning: Unless you are an experienced programmer the kara-templater.lua script is a very bad place to start!
In addition, the Automation 3 scripting interface used in Aegisub 1.10 and earlier is also supported but using the Automation 4 Lua interface is recommended. The Automation 3 environment is reproduced as closely as possible, meaning Lua 5.0 is used instead of Lua 5.1 and all data structures are kept the same. There are however a few minor differences, see more at Moving from Automation 3.
If you have previous experience with writing Automation 3 scripts, there is also an overview of changes from Automation 3.
 Future goals
Apart from the addition of more languages as mentioned above, one major future goal of Automation is to allow custom file format handlers enabling you to make Aegisub read and write almost every imaginable file format so they can be edited with Aegisub.