Scripting aider
You can script aider via the command line or python.
Command line
Aider takes a --message argument, where you can give it a natural language instruction.
It will do that one thing, apply the edits to the files and then exit.
So you could do:
aider --message "make a script that prints hello" hello.js
Or you can write simple shell scripts to apply the same instruction to many files:
for FILE in *.py ; do
    aider --message "add descriptive docstrings to all the functions" $FILE
done
Use aider --help to see all the 
command line options,
but these are useful for scripting:
--stream, --no-stream
                      Enable/disable streaming responses (default: True) [env var:
                      AIDER_STREAM]
--message COMMAND, --msg COMMAND, -m COMMAND
                      Specify a single message to send GPT, process reply then exit
                      (disables chat mode) [env var: AIDER_MESSAGE]
--message-file MESSAGE_FILE, -f MESSAGE_FILE
                      Specify a file containing the message to send GPT, process reply,
                      then exit (disables chat mode) [env var: AIDER_MESSAGE_FILE]
--yes                 Always say yes to every confirmation [env var: AIDER_YES]
--auto-commits, --no-auto-commits
                      Enable/disable auto commit of GPT changes (default: True) [env var:
                      AIDER_AUTO_COMMITS]
--dirty-commits, --no-dirty-commits
                      Enable/disable commits when repo is found dirty (default: True) [env
                      var: AIDER_DIRTY_COMMITS]
--dry-run, --no-dry-run
                      Perform a dry run without modifying files (default: False) [env var:
                      AIDER_DRY_RUN]
--commit              Commit all pending changes with a suitable commit message, then exit
                      [env var: AIDER_COMMIT]
Python
You can also script aider from python:
from aider.coders import Coder
from aider.models import Model
# This is a list of files to add to the chat
fnames = ["greeting.py"]
model = Model("gpt-4-turbo")
# Create a coder object
coder = Coder.create(main_model=model, fnames=fnames)
# This will execute one instruction on those files and then return
coder.run("make a script that prints hello world")
# Send another instruction
coder.run("make it say goodbye")
# You can run in-chat "/" commands too
coder.run("/tokens")
See the Coder.create() and Coder.init() methods for all the supported arguments.
It can also be helpful to set the equivalent of --yes by doing this:
from aider.io import InputOutput
io = InputOutput(yes=True)
# ...
coder = Coder.create(model=model, fnames=fnames, io=io)
The python scripting API is not officially supported or documented, and could change in future releases without providing backwards compatibility.