action article target "\n"
action ::= "WALK" | "FEED" | "PLAY WITH"
target ::= "DOG" | "CAT" | "CANARY" | "FISH"
article ::= "A" | "THE"

##</code><code>##

  WALK THE DOG
  FEED THE CANARY
  PLAY WITH A FISH

##</code><code>##

use strict;
use warnings;

while (my $sLine = <DATA>) {

  my @aFields = split(/\s+/, $sLine);

  #the general case
  my $sAction = shift @aFields;
  my $sArticle = shift @aFields;
  my $sTarget = shift @aFields;

  #special cases - PLAY WITH has two tokens
  if ($sAction eq 'PLAY') {
    $sAction .= " $sArticle";  #$sArticle is 'WITH'
    $sArticle = $sTarget;      #$sTarget is an article
    $sTarget = shift @aFields; #target never got read
  }
  doSomethingWithStatement($sAction, $sArticle, $sTarget);
}

sub doSomethingWithStatement {
  my ($sAction, $sArticle, $sTarget) = @_;
  print "action=<$sAction> article=<$sArticle> target=<$sTarget>\n";
}

__DATA__
WALK THE DOG
FEED THE FISH
PLAY WITH A CANARY