my $range = "2..5,10..15";

# Split on commas
my @range = split /,/, $range;

# Expand any n..m
@range = map { /(\d+)..(\d+)/ ? ($1..$2) : $_ } @range;
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Assuming the resulting @range is small (where small is, say, less than 10,000 elements) this will do fine. Error checking is left as an exercise for the reader.