Ask HN: Push new posts in a Slack channel to another app?

Is there an API to pull new messages in a Slack channel? Or an integration so new messages in a Slack channel are pushed to another app?

I have users posting URLs in a slack channel and I would like to be able to programmatically add those URLs to a text file on my server as they arrive in the Slack channel... rather than me manually pointy-clicky-copy-paste every afternoon.

thanks for any suggestions/pointers!