use strict;
use Data::Dumper;

my $network_ifs = `netstat -i | grep -Ev "lo|sit|link|Name" | cut -f1 -d" " | uniq | sort -n`;

my @tcp_utilization_metrics = split '\n', $network_ifs;

my %tcp_utilization_adapter_names;

foreach my $network_if (@tcp_utilization_metrics) {
    next if ! $network_if; # ignore empty lines if any
    my $if_name = $network_if;

    if ($network_if =~ /en/) {
        substr($network_if, 2, 0) = "t";   # insert 't'
    } elsif ($network_if =~ /tr/) {
        substr($network_if, 1, 2) = "ok";  # replace 'ok'
    } elsif ($network_if =~ /at/) {
        substr($network_if, 2, 0) = "m";   # insert 'm'
    }
    # insert hash entries
    $tcp_utilization_adapter_names{$if_name} = $network_if;
}

# investigate the hash
foreach (keys %tcp_utilization_adapter_names) {
    print "$tcp_utilization_adapter_names{$_}\n";
}