Here are some of the things I think you'll want to know as you write a Perl script to do what your shell script does:

• Start with "use strict;use warnings;". Read Use strict and warnings for details. You'll have to use my because of this.
• You'll probably want a loop that starts with "while ( my $line = <> )". You may want to use open.
• chomp
• split
• Regular expressions will be very useful, so have a look at perlretut. For example:

  if ( $line =~ /(\d+:\d\d):\d\d (?:GMT|SAST)/ ) {
      my $the_hour_and_minute = $1;
  }
  [download]

• I'd be tempted to use the range operator to capture things between /^vmstat/ and /^END/, but using a flag as you have already will still work.
• print, warn, die

I'll note also that vmstat has a -n option which causes it to output the header only once. You could send that through tail before it ever gets to the log, and your processor would not have to deal with those lines at all.