ifstat

$ ifstat -t -i eth0 -n 1 > /tmp/ifstat2

  Time           eth0
HH:MM:SS   KB/s in  KB/s out
15:00:41      0.00      0.00
15:00:42      0.59      0.00
15:00:43      0.00      0.00
15:00:44   3861.10    101.12
15:00:45   4315.10     79.13
15:00:46   2657.83     51.41
15:00:47   1595.16     27.43
15:00:48   1794.52     32.43
15:00:49   2256.26     53.87
15:00:50   1566.12     46.48
15:00:51   1527.59     39.65
15:00:52   1414.66     28.87
15:00:53   1491.90     29.94
15:00:54   1663.79     36.29
15:00:55   3123.90     96.32
15:00:56   2148.78     45.94
15:00:57   1720.19     32.65
15:00:58   1716.53     37.81
15:00:59   7337.86    133.70
15:01:00   8847.76    159.43
15:01:01   9788.41    174.11
15:01:02   8407.27    162.51
15:01:03   9644.86    190.40
15:01:04  10142.09    213.84
15:01:05  10415.12    242.86
15:01:06  10150.22    222.91
15:01:07   9361.39    206.49
15:01:08   9975.20    218.03

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$ ifstat -t -i eth0 -n -b 1 > /tmp/ifstat2

  Time           eth0
HH:MM:SS   Kbps in  Kbps out
15:03:22      1.03      1.03
15:03:23      0.93      0.00
15:03:24    409.74    153.88
15:03:25    358.57     33.60
15:03:26      0.72      0.00
15:03:27     80.02     58.20
15:03:28    127.59     15.22
15:03:29  33946.10    736.39
15:03:30  17141.32    348.80
15:03:31  11077.98    216.84
15:03:32  12464.92    214.67
15:03:33  14359.15    260.90