#include <StringConstants.au3> ; to declare the Constants of StringRegExp
#include <Array.au3> ; UDF needed for _ArrayDisplay and _ArrayConcatenate
Local $sRegex = "http(?:s)?:\/\/(?:www\.)?youtube\.com\/.*?watch%3Fv%([\d\w-_]+)"
Local $sString = "http://youtube.com/attribution_link?a=r_FgjB-RKNo&u=/watch%3Fv%3DB0_X8zWJd0Q%26feature%3Dem-uploademail" & @CRLF & _
"http://youtube.com/attribution_link?a=1crTn2Lx38I&u=/watch%3Fv%3DHhebhh2s5d4%26feature%3Dem-uploademail" & @CRLF & _
"http://youtube.com/attribution_link?a=_zMgiznzBto&u=/watch%3Fv%3D-kaoCPvUHJM%26feature%3Dem-uploademail" & @CRLF & _
"http://youtube.com/attribution_link?a=F8VReY1sT0A&u=/watch%3Fv%3D5RLM9rk0Q8s%26feature%3Dem-uploademail" & @CRLF & _
"https://www.youtube.com/watch?feature=player_detailpage&v=2eGUP16P_p4" & @CRLF & _
""
Local $aArray = StringRegExp($sString, $sRegex, $STR_REGEXPARRAYGLOBALFULLMATCH)
Local $aFullArray[0]
For $i = 0 To UBound($aArray) -1
_ArrayConcatenate($aFullArray, $aArray[$i])
Next
$aArray = $aFullArray
; Present the entire match result
_ArrayDisplay($aArray, "Result")
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