# a=463.3742.23
# b=99
sub getFoo{

    my $a;
    my $b;
    my $strFoo;

    ($a,$b) = @_;

    $strFoo .= $a;
    $strFoo .= "_";
    $strFoo .= $b;
    $strFoo .= "_testme";
    $strFoo .= ".xml";

    return $strFoo;
}

Result:
$strFoo=463.3742.23_99_testme.xml


##</code><code>##

# single value passed in = 463.3742.23
sub getFoo{

    my $strFoo = @_;
    $strFoo .= "_testme";
    $strFoo .= ".xml";

    return $strFoo;
}

Result:
$strFoo=463.3742.23_testme.xml
*or*
$strFoo=1_testme.xml