The /sbin/lspci utility is handy on Linux. I'm not sure how portable it is.

my @nics = do {
    open my $pci, '-|', '/sbin/lspci' or die $!;
    grep { /Ethernet controller/ } <$pci>;
};
# 00:08.0 Ethernet controller: 3Com Corporation 3c905B 100BaseTX [Cycl
+one] (rev 30)
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