my $last= ( " AB CDE FG HI JKL " =~ /( \w\w )/g )[-1];
print $last, $/;
__END__
prints " FG " (not " HI ")

##</code><code>##

my( $last )= " AB CDE FG HI JKL " =~ /.*(\w+)/sg;
print $last, $/;
__END__
prints "L" (not "JKL")

##</code><code>##

my $string= " AB CDE FG HI JKL ";
my $PATTERN= qr/(?! F)(?: \w+){1,3} /;
# (match space-separated words where the first doesn't start with "F")
my( $last )= $string =~ /.*($PATTERN)/sg;
print $last, $/;
$last= ( $string =~ /($PATTERN)/g )[-1];
print $last, $/;
__END__
prints:
 JKL
 JKL
never:
 HI JKL 

##</code><code>##

my $string= reverse " AB CDE FG HI JKL ";
my $PATTERN= qr/(?: \w+){1,3}(?<!F) /;
# (match space-separated words where the last doesn't end with "F")
my $last= $string =~ /($PATTERN)/ ? $1 : undef;
print reverse($last) . $/;
__END__
prints " HI JKL " !

##</code><code>##

my $string= " AB CDE FG HI JKL ";
my $PATTERN= qr/(?! F)(?: \w+){1,3} /;
# (match space-separated words where the first doesn't start with "F")
my $last;
my $end= -1;
while(  $string =~ /(?=($PATTERN))/g  ) {
    my $stop= $+[-1];
    if(  $end < $stop  ) {
        $last= $1;
        $end= $stop;
    }
}
print $last, $/;
__END__
prints " HI JKL " !