arcstat.pl is a Perl script that uses the Sun::Solaris::Kstat module to read
ZFS ARC kstat values from the system and report on an interval basis. 

Some output examples can be found on the author's blog here:
http://blogs.sun.com/realneel/entry/zfs_arc_statistics

Examples showing L2ARC data can be found here:
http://blog.harschsystems.com/tools/arcstat-pl-updated-for-l2arc-statistics/

Note: L2ARC statistics are only available on systems that have implemented
the L2ARC (i.e. nevada-based releases).

Usage for arcstat.pl can be obtained by providing the "--help" flag:

./arcstat.pl --help
Arcstat version 0.4b + Solaris 11
I have made a minor change as the original version would not work on my Solaris 11 server (a diffrent name in kststs for l2 arc size (l2_hdr_size as aposed to l2_size)
Usage: arcstat.pl [-hvxr] [-f fields] [-o file] [interval [count]]
         -x : Print extended stats
         -r : Raw Output mode (values not scaled)
         -f : Specify specific fields to print (see -v)
         -o : Print stats to file
         -s : Specify a seperator

Examples:
        arcstat -o /tmp/a.log 2 10
        arcstat -s , -o /tmp/a.log 2 10
        arcstat -v
        arcstat -f time,hit%,dh%,ph%,mh% 

Available fields (statistics) can be retrieved with the "-v" flag:

./arcstat.pl -v
Arcstat version 0.4
Usage: arcstat.pl [-hvxr] [-f fields] [-o file] [interval [count]]
Field definitions are as follows
 mtxmis : mutex_miss per second
  arcsz : Arc Size
   mrug : MRU Ghost List hits per second
 l2hit% : L2ARC access hit percentage
    mh% : Metadata hit percentage
l2miss% : L2ARC access miss percentage
   read : Total Arc accesses per second
      c : Arc Target Size
   mfug : MFU Ghost List hits per second
   miss : Arc misses per second
    dm% : Demand Data miss percentage
   dhit : Demand Data hits per second
  pread : Prefetch accesses per second
  dread : Demand data accesses per second
   pmis : Prefetch misses per second
 l2miss : L2ARC misses per second
   time : Time
l2bytes : bytes read per second from the L2ARC
    pm% : Prefetch miss percentage
    mm% : Metadata miss percentage
   hits : Arc reads per second
    mfu : MFU List hits per second
 l2read : Total L2ARC accesses per second
   mmis : Metadata misses per second
   rmis : recycle_miss per second
   mhit : Metadata hits per second
   dmis : Demand Data misses per second
    mru : MRU List hits per second
    ph% : Prefetch hits percentage
  eskip : evict_skip per second
 l2size : Size of the L2ARC
 l2hits : L2ARC hits per second
   hit% : Arc Hit percentage
  miss% : Arc miss percentage
    dh% : Demand Data hit percentage
  mread : Metadata accesses per second
   phit : Prefetch hits per second