Use Getopt::Std to parse the options for you then check that you got everything:

use strict;
use warnings;
use Getopt::Std;

my %opts;

getopts('b:l:', \%opts);

if (! exists $opts{b} || ! exists $opts{l}) {
    die "Both -b and -l options are required\n";
}

print "-b: $opts{b}, -l $opts{l}\n";
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