Using vbscript regular expression to conditional replace dates - regex

Question

I would like to use regex to replace the actual dates in the string to YYYYMMDD. However, my string might contain 2 types of dates, it could either be 20160531 or 160531. For these two, I have to replace them with YYYYMMDD and YYMMDD. So the followings are two examples:
Employment_salary_20160531 -> Employment_salary_YYYYMMDD
Employment_salary_160531 -> Employment_salary_YYMMDD
Wondering if it is possible to do this within a single regex without using an IFELSE statement?
Thank you!

Answer 1

This will provide you with accurate validation of the date that's entered. The other regex will work but it's dirty. It will accept 5000 as year.
The short answer: ((19|20)\d{2}|[0-9]{2})(0[1-9]|1[0-2])([012][0-9]|3[0-1])
The Long but thoroughly tested answer...
stringtest1 = "Employment_salary_20160531"
stringtest2 = "Employment_salary_990212"
stringtest3 = "Employment_salary_990242"
wscript.echo : wscript.echo "---------------------------------------------------" : wscript.echo
wscript.echo "Trying: " & stringtest1 & vbcrlf & vbcrlf & vbtab & " => " & sanitizedate(stringtest1)
wscript.echo : wscript.echo "---------------------------------------------------" : wscript.echo
wscript.echo "Trying: " & stringtest2 & vbcrlf & vbcrlf & vbtab & " => " & sanitizedate(stringtest2)
wscript.echo : wscript.echo "---------------------------------------------------" : wscript.echo
wscript.echo "Trying: " & stringtest3 & vbcrlf & vbcrlf & vbtab & " => " & sanitizedate(stringtest3)
wscript.echo : wscript.echo "---------------------------------------------------" : wscript.echo
Function sanitizedate(str)
Set objRE = New RegExp
objRE.Pattern = "((19|20)\d{2}|[0-9]{2})(0[1-9]|1[0-2])([012][0-9]|3[0-1])"
objRE.IgnoreCase = True
objRE.Global = False
objRE.Multiline = true
Set objMatch = objRE.Execute(str)
If objMatch.Count = 1 Then
Select Case Len(objMatch.Item(0))
Case "8"
sanitizedate = Replace(str, objMatch.Item(0), "YYYYMMDD")
Case "6"
sanitizedate = Replace(str, objMatch.Item(0), "YYMMDD")
End Select
Else
sanitizedate = str
End if
End Function
Validation Results
Trying: Employment_salary_20160531
=> Employment_salary_YYYYMMDD
Trying: Employment_salary_990212
=> Employment_salary_YYMMDD
Trying: Employment_salary_990242 failed because 42 is not a valid date
=> Employment_salary_990242

Answer 2

I'm not sure I get you right. But seems there is two different replacement YYYYMMDD and YYMMDD which doing that is impossible by just one single pattern.
You can match those two separated pattern by this:
/(^(\d{4})(\d{2})(\d{2})$)|(^(\d{2})(\d{2})(\d{2})$)/
Online Demo
As you see, pattern above matches both 20160531 and 160531. But you cannot replace them with both YYYYMMDD (for 20160531) and YYMMDD (for 160531). You actually can replace them with either YYYYMMDD or YYMMDD.
Otherwise you need two separated patterns if you want two separated replacements:
/^(\d{4})(\d{2})(\d{2})$/
/* and replace with `YYYYMMDD` */
/^(\d{2})(\d{2})(\d{2})$/
/* and replace with YYMMDD */