#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = ""\K[\w-]+(\.jpg)(?=")"
Local $sString = ";s:27:"2018/08/hello-there-003.jpg";s:5:"sizes";a:23:{s:9:"thumbnail";a:4:{s:4:"file";s:27:"hello-there-003-150x150.jpg";s:5:"width";i:150;s:6:"height";i:150;s:9:"mime-type";s:10:"image/jpeg";}s:6:"medium";a:4:{s:4:"file";s:27:"hello-there-003-300x200.jpg"" & @CRLF & _
""
Local $sSubst = "replacement$1"
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