When extracting configuration data from managed network gear such as Juniper or Cisco switches, consecutive vlans are combined into ranges "from-to". Given a $list of vlans such as "2-4,10-12" I needed an @array of every single vlan. An easy way to accomplish this is to make use of Perl's ".." range operator like so:
my $list = "2-4,10-12";
$list =~ s/\-/../g;
my @array = eval( $list );
# @array is now (2,3,4,10,11,12)
So far so good. What I'm looking for is an equally simple way to reverse the process. I mashed together the following code to get the job done but it's just painful to look at:
my @array = (2,3,4,10,11,12);
my @vlans = ();
my $span = undef;
my $last = undef;
foreach my $vlan (sort @array) {
if (defined $last && $vlan == $last+1) {
unless (defined $span) {
$span = $last;
}
$vlans[$#vlans] = $span.'-'.$vlan;
} else {
push @vlans, $vlan;
$span = undef;
}
$last = $vlan;
}
my $list = join(',', @vlans);
# $list is now "2-4,10-12" again
Surely there must be a better way?!
Edit: Single elements should appear like "2-4,7,10-12,20". Sorry for not pointing this out.
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