#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "<\?(?!php)"
Local $sString = "<?" & @CRLF & _
"$var1 = "This is just some dummy test.";" & @CRLF & _
"echo $var1;" & @CRLF & _
"?>" & @CRLF & _
"Leave this tag alone:" & @CRLF & _
"<?php" & @CRLF & _
"echo $var2;" & @CRLF & _
"?>"
Local $sSubst = "<?php"
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