perl -ne '$string=$_ if /Successfully sent/;  END{print $string}' $logfile

##</code><code>##


2017-11-02 12:08:11,120 INFO [Timer-Driven Process Thread-8] o.a.nifi.remote.StandardRemoteGroupPort RemoteGroupPort[name=Receiver,targets=https://host.sub.domain.tld:9443/nifi] Successfully sent [StandardFlowFileRecord[uuid=xxxxxxxxxxxx,claim=StandardContentClaim [resourceClaim=StandardResourceClaim[id=xxx, container=default, section=xxx], offset=384244, length=163820],offset=0,name=xxxxx.json,size=163820]] (159.98 KB) to https://host.sub.domain.tld:9443/nifi-api in 242 milliseconds at a rate of 660.28 KB/sec


##</code><code>##

perl -ne '$string=$_ if /Successfully sent/;  $string =~ /^(.*) INFO.*$/; END{print $1}' $logfile