Line 21 is this line:

my $result = $session->get_next_request ( varbindlist => [ $param{sysN
+ame}.$1] ); die "request error: ".$session->error unless ( defined $r
+esult );
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The reason that your program breaks is that it directly calls "die" which brings the script to an immediate end... see die for the details. I think that if you change it to "warn" or even a plain "print" it will do what you are looking for. For similar reasons, you will also need to change

unless ( $param{sysName} =~ /$param{sysName}(.*)/ ) {last}
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on the next line to

unless ( $param{sysName} =~ /$param{sysName}(.*)/ ) {next}
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since the "last" will exit the loop so no more ip's will be tried.