kvale provides a point well taken. Still, the relevance or need for quotes around a variable name actually depend on the context -- we'd need to see the code where $userid is actually being assigned to and used, to tell whether the use of quotes is really necessary. As a rule, I think Perl normally does the right thing with strings consisting of many digits. Consider:

$s1 = "01234567891233456789";
$s2 = "012345.6789123456789"; 

$n1 = $s1+1; 
$n2 = $s2+1; 

$c1 = $s1;
$c2 = $s2;

print "$n1 == $s1 + 1\n";
print "$n2 == $s2 + 1\n";
print "$c1 eq $s1\n";
print "$c2 eq $s2\n";

__OUTPUT__
1.23456789123346e+18 == 01234567891233456789 + 1
12346.6789123457 == 012345.6789123456789 + 1
01234567891233456789 eq 01234567891233456789
012345.6789123456789 eq 012345.6789123456789
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The assignments to $n1 and $n2, happening in numeric context, cause a loss of precision -- as well as removal of leading zeros, but using $s1 and $s2 in a numeric context does not cause a change in the string value that was originally assigned to these variables: if a variable is originally assigned a value in a string context, it will always return that value when used in a string context.

The other thing to note is that the "default" value assignment operation is a string assignment, unless rhs variable's original value was obtained/created in a numeric context.