We have this config:
[threatlist://ransomware_ip_blocklist] 
delim_regex = : 
description = abuse.ch Ransomware Blocklist 
disabled = false 
fields = ip:$1,description:Ransomware_ip_blocklist 
type = threatlist 
url = https://ransomwaretracker.abuse.ch/downloads/RW_IPBL.txt
Why we wrote there $1? What it's mean? (Yes, it's mean IP, it's regular that will pars all IP?
$1 is the value for the ip field. Refer to documentation here : http://docs.splunk.com/Documentation/ES/4.7.3/Admin/Downloadthreatfeed
$1 is the value for the ip field. Refer to documentation here : http://docs.splunk.com/Documentation/ES/4.7.3/Admin/Downloadthreatfeed