#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?m)([0-9A-F]{2}:){5}[0-9A-F]{2}"
Local $sString = "[DHCP IP: (192.168.1.17)] to MAC address 00:50:8D:91:40:A3, Monday, Aug 10,2020 21:06:09" & @CRLF & _
"[DHCP IP: (192.168.1.11)] to MAC address 00:FA:21:46:F0:70, Monday, Aug 10,2020 19:41:28" & @CRLF & _
"[DHCP IP: (192.168.1.14)] to MAC address 8C:79:67:C1:C4:F7, Monday, Aug 10,2020 19:41:12" & @CRLF & _
"[DHCP IP: (192.168.1.7)] to MAC address 00:1C:C0:F0:8A:94, Monday, Aug 10,2020 16:51:41" & @CRLF & _
"[DHCP IP: (192.168.1.17)] to MAC address 00:50:8D:91:40:A3, Monday, Aug 10,2020 15:53:03" & @CRLF & _
"[DHCP IP: (192.168.1.12)] to MAC address 0C:62:A6:E4:60:A6, Monday, Aug 10,2020 15:48:05" & @CRLF & _
"[Dynamic DNS] host name 520techsec.hopto.org registration successful, Monday, Aug 10,2020 14:29:55" & @CRLF & _
"[Dynamic DNS] host name 520techsec.hopto.org registration failure, Monday, Aug 10,2020 14:29:24" & @CRLF & _
"[Dynamic DNS] host name 520techsec.hopto.org registration failure, Monday, Aug 10,2020 14:28:53" & @CRLF & _
"[Dynamic DNS] host name 520techsec.hopto.org registration failure, Monday, Aug 10,2020 14:28:22" & @CRLF & _
"[DHCP IP: (192.168.1.10)] to MAC address 6C:C2:17:1E:B4:B9, Monday, Aug 10,2020 09:51:03" & @CRLF & _
"[DHCP IP: (192.168.1.17)] to MAC address 00:50:8D:91:40:A3, Monday, Aug 10,2020 09:04:50" & @CRLF & _
"[DHCP IP: (192.168.1.11)] to MAC address 00:FA:21:46:F0:70, Monday, Aug 10,2020 08:10:16" & @CRLF & _
"[DHCP IP: (192.168.1.14)] to MAC address 8C:79:67:C1:C4:F7, Monday, Aug 10,2020 08:10:01" & @CRLF & _
"[DHCP IP: (192.168.1.13)] to MAC address 00:16:44:DF:C7:92, Monday, Aug 10,2020 07:11:22" & @CRLF & _
"[DHCP IP: (192.168.1.13)] to MAC address 00:16:44:DF:C7:92, Monday, Aug 10,2020 07:04:23" & @CRLF & _
"[DHCP IP: (192.168.1.7)] to MAC address 00:1C:C0:F0:8A:94, Monday, Aug 10,2020 04:51:42" & @CRLF & _
"[DHCP IP: (192.168.1.17)] to MAC address 00:50:8D:91:40:A3, Monday, Aug 10,2020 03:52:41" & @CRLF & _
"[DHCP IP: (192.168.1.12)] to MAC address 0C:62:A6:E4:60:A6, Monday, Aug 10,2020 03:48:20" & @CRLF & _
"[DHCP IP: (192.168.1.10)] to MAC address 6C:C2:17:1E:B4:B9, Sunday, Aug 09,2020 21:15:05" & @CRLF & _
"[DHCP IP: (192.168.1.17)] to MAC address 00:50:8D:91:40:A3, Sunday, Aug 09,2020 21:06:42" & @CRLF & _
"[DHCP IP: (192.168.1.8)] to MAC address 9C:B6:D0:73:52:AB, Sunday, Aug 09,2020 20:53:45" & @CRLF & _
"[DHCP IP: (192.168.1.11)] to MAC address 00:FA:21:46:F0:70, Sunday, Aug 09,2020 20:39:03" & @CRLF & _
"[DHCP IP: (192.168.1.14)] to MAC address 8C:79:67:C1:C4:F7, Sunday, Aug 09,2020 20:38:48" & @CRLF & _
"[DHCP IP: (192.168.1.8)] to MAC address 9C:B6:D0:73:52:AB, Sunday, Aug 09,2020 20:33:15" & @CRLF & _
"[DHCP IP: (192.168.1.7)] to MAC address 00:1C:C0:F0:8A:94, Sunday, Aug 09,2020 16:51:41" & @CRLF & _
"[DHCP IP: (192.168.1.17)] to MAC address 00:50:8D:91:40:A3, Sunday, Aug 09,2020 15:53:06" & @CRLF & _
"[DHCP IP: (192.168.1.12)] to MAC address 0C:62:A6:E4:60:A6, Sunday, Aug 09,2020 15:48:33" & @CRLF & _
"[Dynamic DNS] host name 520techsec.hopto.org registration successful, Sunday, Aug 09,2020 14:28:12" & @CRLF & _
"[Dynamic DNS] host name 520techsec.hopto.org registration failure, Sunday, Aug 09,2020 14:27:41" & @CRLF & _
"[Dynamic DNS] host name 520techsec.hopto.org registration failure, Sunday, Aug 09,2020 14:27:10" & @CRLF & _
"[Dynamic DNS] host name 520techsec.hopto.org registration failure, Sunday, Aug 09,2020 14:26:38" & @CRLF & _
"[DHCP IP: (192.168.1.11)] to MAC address 00:FA:21:46:F0:70, Sunday, Aug 09,2020 09:07:51" & @CRLF & _
"[DHCP IP: (192.168.1.14)] to MAC address 8C:79:67:C1:C4:F7, Sunday, Aug 09,2020 09:07:37" & @CRLF & _
"[DHCP IP: (192.168.1.17)] to MAC address 00:50:8D:91:40:A3, Sunday, Aug 09,2020 09:05:37"
Local $sSubst = ""
Local $sResult = StringRegExpReplace($sString, $sRegex, $sSubst)
MsgBox($MB_SYSTEMMODAL, "Result", $sResult)
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for AutoIt, please visit: https://www.autoitscript.com/autoit3/docs/functions/StringRegExp.htm