#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "NF.*?(\d*)\|.*"
Local $sString = "NF3-9-16S_S9_1456|M02255:210:000000000-B9K3P:1:1101:14397:18152 1:N:0:9|o:50|m/o:0.720000|MR:n=0;r1=34;r2=2|Q30:p=97;p=100|CO:0|mismatches:36" & @CRLF & _
"" & @CRLF & _
"NF3-9-16S_S9_9999|M02255:210:000000000-B9K3P:1:1101:14397:18152 1:N:0:9|o:50|m/o:0.720000|MR:n=0;r1=34;r2=2|Q30:p=97;p=100|CO:0|mismatches:36"
Local $sSubst = "Re1_91910_$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