#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?m)^172\.18\.(([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])\.)([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-9])$"
Local $sString = "172.18.0.255" & @CRLF & _
"185.25.14.263" & @CRLF & _
"172.15.12.0" & @CRLF & _
"172.18.255.255" & @CRLF & _
""
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