Slack – How to see all the Slack activity within a period

To actually "slack-archive" the channels, ie the equivalent of running "/archive" within each channel, you'll need some API magic.

First, set up an API token for your user in the relevant team on https://api.slack.com/custom-integrations/legacy-tokens, then go to https://api.slack.com/methods/channels.list/test to get a json-listing of your channels together with the channel ids.

Then use these channel ids to run https://api.slack.com/methods/channels.archive/test for the channels you want to archive.

Here is a quick and dirty bash script (which uses jq) I recently ran on my Mac in order to archive the hundreds of channels that contained "sk-" in the channel name:

TOKEN="replace-this-with-your-user-api-token-in-the-relevant-team"
curl "https://slack.com/api/channels.list?token=$TOKEN&exclude_archived=true&pretty=1" > /tmp/channels.list
IDS=$(cat /tmp/channels.list | jq '.channels[] | select(.name | contains("sk-")) | .id' | sed -e 's/"//g')
for ID in $IDS; do
    URL="https://slack.com/api/channels.archive?token=$TOKEN&channel=$ID&pretty=1"
    echo $URL
    curl "$URL"
done

It got the job done, archiving about 2-3 channels per second.

As far as I know you can not do that from the UI, but you can certainly create an app that performs this task via the API. Slack has a sophisticated conversations API that allows to query and manipulate all channels of a Slack team including public and private channels.

There is one caveat though. Due to Slack's security architecture no user has access to a private channel, he/she is not invited to. That also applies to admins. So an app like this will only work for private channels if the user authorizing the app is a member of all private channels.

One way to achieve that is to have a generic admin user (e.g. "slackadmin") as mandatory member in all private channel and use that generic admin user to authenticate the app.

We actually have an app our team that automatically and constantly invites / kicks users to private channels based on their membership status and we use the generic admin user approach to achieve that.