use strict;
use warnings;

my $state;
my $firstAttempt = 1;

while (1) {
    if($firstAttempt) {
        $state = promptUser("What network to listen for SNMP traps [hsbn or admin]? ", "admin"); ;
        $firstAttempt = 0;
    } else {
        $state = lc promptUser("ERROR: $state Invalid Re-enter the network");
    }
    
    if (0 == index 'hsbn', $state) {
        $state = 'hsbn';
        last;
    } elsif (0 == index 'admin', $state) {
        $state = 'admin';
        last;
    }
}

if ($state eq 'hsbn') {
    #some action
}