Slack clean all messages (~8K) in a channel

Question

We currently have a Slack channel with ~8K messages all comes from Jenkins integration. Is there any programmatic way to delete all messages from that channel? The web interface

Answer 1

Option 1 You can set a Slack channel to automatically delete messages after 1 day, but it's a little hidden. First, you have to go to your Slack Workspace Settings, Message Retention & Deletion, and check "Let workspace members override these settings". After that, in the Slack client you can open a channel, click the gear, and click "Edit message retention..."

Option 2 The slack-cleaner command line tool that others have mentioned.

Option 3 Below is a little Python script that I use to clear Private channels. Can be a good starting point if you want more programmatic control of deletion. Unfortunately Slack has no bulk-delete API, and they rate-limit the individual delete to 50 per minute, so it unavoidably takes a long time.

# -*- coding: utf-8 -*-
"""
Requirement: pip install slackclient
"""
import multiprocessing.dummy, ctypes, time, traceback, datetime
from slackclient import SlackClient
legacy_token = raw_input("Enter token of an admin user. Get it from https://api.slack.com/custom-integrations/legacy-tokens >> ")
slack_client = SlackClient(legacy_token)


name_to_id = dict()
res = slack_client.api_call(
  "groups.list", # groups are private channels, conversations are public channels. Different API.
  exclude_members=True, 
  )
print ("Private channels:")
for c in res['groups']:
    print(c['name'])
    name_to_id[c['name']] = c['id']

channel = raw_input("Enter channel name to clear >> ").strip("#")
channel_id = name_to_id[channel]

pool=multiprocessing.dummy.Pool(4) #slack rate-limits the API, so not much benefit to more threads.
count = multiprocessing.dummy.Value(ctypes.c_int,0)
def _delete_message(message):
    try:
        success = False
        while not success:
            res= slack_client.api_call(
                  "chat.delete",
                  channel=channel_id,
                  ts=message['ts']
                )
            success = res['ok']
            if not success:
                if res.get('error')=='ratelimited':
#                    print res
                    time.sleep(float(res['headers']['Retry-After']))
                else:
                    raise Exception("got error: %s"%(str(res.get('error'))))
        count.value += 1
        if count.value % 50==0:
            print(count.value)
    except:
        traceback.print_exc()

retries = 3
hours_in_past = int(raw_input("How many hours in the past should messages be kept? Enter 0 to delete them all. >> "))
latest_timestamp = ((datetime.datetime.utcnow()-datetime.timedelta(hours=hours_in_past)) - datetime.datetime(1970,1,1)).total_seconds()
print("deleting messages...")
while retries > 0:
    #see https://api.slack.com/methods/conversations.history
    res = slack_client.api_call(
      "groups.history",
      channel=channel_id,
      count=1000,
      latest=latest_timestamp,)#important to do paging. Otherwise Slack returns a lot of already-deleted messages.
    if res['messages']:
        latest_timestamp = min(float(m['ts']) for m in res['messages'])
    print datetime.datetime.utcfromtimestamp(float(latest_timestamp)).strftime("%r %d-%b-%Y")

    pool.map(_delete_message, res['messages'])
    if not res["has_more"]: #Slack API seems to lie about this sometimes
        print ("No data. Sleeping...")
        time.sleep(1.0)
        retries -= 1
    else:
        retries=10

print("Done.")

Note, that script will need modification to list & clear public channels. The API methods for those are channels.* instead of groups.*