Here is a sample script using a general purpose UDF.

Break ON

$sLCASE="abcdefghijklmnopqrstuvwxyz"
$sUCASE="ABCDEFGHIJKLMNOPQRSTUVWXYZ"
$sNumerics="0123456789"

$sString="FOObar123"

"Upper case characters in string: '"+udfGetChars($sString,$sUCASE)+"'"+@CRLF
"Lower case characters in string: '"+udfGetChars($sString,$sLCASE)+"'"+@CRLF
"Alpha characters in string: '"+udfGetChars($sString,$sLCASE+$sUCASE)+"'"+@CRLF
"Numeric characters in string: '"+udfGetChars($sString,$sNumerics)+"'"+@CRLF

Function udfGetChars($s,$sMatch)
        Dim $SO
        $udfGetChars=""
        $SO=SetOption("CaseSensitivity","ON")
        While $s<>""
                If InStr($sMatch,Left($s,1)) $udfGetChars=$udfGetChars+Left($s,1) EndIf
                $s=SubStr($s,2)
        Loop
        $SO=SetOption("CaseSensitivity",$SO)
EndFunction



Output:

 Quote:
Upper case characters in string: 'FOO'
Lower case characters in string: 'bar'
Alpha characters in string: 'FOObar'
Numeric characters in string: '123'