my ($temp) = 121, 122, 123, 124, 125, etc...

my $temp = "121, 122, 123, 124, 125, 126";
my @userids = split /\s*,\s*/, $temp;
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This will split your scalar containing a comma-separated list of values into an array containing each of those values. The array will automagically have as many elements as necessary.