...## get $fh from somewhere (eg.open)
my $last = '';
while( <$fh> ) {
    ( $last . $_ ) =~ m[cpuinfo\nvendor_id\s+:\s(.*?)\n] 
        and print qq[CPU:$1] and last; 
    $last = $_;
}
...

##</code><code>##

perl -ne"($last.$_)=~m[cpuinfo\nvendor_id\s+:\s(.*?)\n]&&print qq[CPU:$1]&&exit;$last=$_" yourfile