How to get the number of interrupts per second

[Federico Giannici]

I have to get (via command line) the number of interrupts per seconds in 
a given moment (OpenBSD 5.5 amd64).

I noticed that the number shown by vmstat is different from the one 
shown from systat. For example, here are the interrupts shown from systat:

 Interrupts
16457 total
  400 clock
    1 ipi
 7894 em1
    1 ehci0
 8161 em3
      ehci1
      ahci0
      ichiic0

And at the same moment this is the output of vmstat:

 procs    memory       page                    disks    traps          cpu
 r b w    avm     fre  flt  re  pi  po  fr  sr sd0 sd1  int   sys   cs 
us sy id
 1 2 0  35852 7717980  269   0   0   0   0   0   0   0 12181   499   23 
 0 13 87


It seems that the systat values are more realistic but I wasn't able to 
"capture" them in a non interactive way. It seems that "-b" or "-B" 
options don't work in the "vmstat" view of systat. As I specify the "-b" 
or "-B" options the only output is:

   2 users    Load 0.29 0.33 0.33                     Wed Jan 28 
11:35:11 2015


So:

1) Is there a way to capture the "systat vmstat" output?

2) Why systat and vmstat give different values?


Thanks.