#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?m).*\b(PAL)\s?(\d+)\b.*"
Local $sString = "TCNU1573105 HDPE HTA108 155 155 000893520918 PAL990 25.2750 MT 28.9750 MT" & @CRLF & _
"TCNU1573105 HDPE HTA108 155 155 000893520918 PAL 990 25.2750 MT 28.9750 MT"
Local $sSubst = "$1$2"
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