my %oids = (
    "ifName" => {
         1 => "Gi1/0/1",
         2 => "Gi1/0/0",
         3 => "Gi1/1/1",
         4 => "Gi2/0/0",
         5 => "Gi2/0/1",
    },
);

##</code><code>##

- or:
my %oids = (
    "ifName" => {
         1 => "1",
         2 => "2",
         3 => "3",
         4 => "4",
         5 => "5",
    },
);
- or:
my %oids = (
    "ifName" => {
         1 => "2/1",
         2 => "4/5",
         3 => "15/1",
         4 => "1/1",
         5 => "1/2",
    },
);
- or:
my %oids = (
    "ifName" => {
         1 => "Fa0/1",
         2 => "Fa0/2",
         3 => "Fa3/1",
         4 => "Gi0/1",
         5 => "Gi0/0",
    },
);

##</code><code>##

my (@a, @b);
my @port_ifIndices = sort {
    if ($oids{ifName}{$a} =~ /\//) {
        @a = split(/\//, $oids{ifName}{$a});
        @b = split(/\//, $oids{ifName}{$b});
    }
    else {
        @a = $oids{ifName}{$a};
        @b = $oids{ifName}{$b};
    }
    if ($a[0] =~ /[A-Za-z]/) {
        $a[0] ne $b[0] ? $a[0] cmp $b[0] : ($a[1] <=> $b[1] ? $a[1] <=> $b[1] : $a[2] <=> $b[2]);
    } else {
        $a[0] != $b[0] ? $a[0] <=> $b[0] : ($a[1] <=> $b[1] ? $a[1] <=> $b[1] : $a[2] <=> $b[2]);
    }
} keys(%{ $oids{ifName} });

foreach my $ifIndex (@port_ifIndices) {
        print ("$ifIndex: $oids{ifName}{$ifIndex}\n");
}

##</code><code>##

2: Gi1/0/0
1: Gi1/0/1
3: Gi1/1/1
4: Gi2/0/0
5: Gi2/0/1