DB<100> $l.="$_\t".(int rand 2)."\n" for 1..1e6  # linenumber TAB 0||1 RET

  DB<101> length $l
 => 8888896

  DB<102> use Time::HiRes qw/time/

  DB<103> sub timeit (&) {
           my $s=time;
           (shift)->();
           print "<",time-$s.">\n";
           }

  DB<104> $i=0; timeit { $i++ while ( $l =~ /\t1\n/g) }; print $i
<0.454659938812256>
500338

  DB<105> $i=0; timeit { $i = () = $l =~ /\t1\n/g }; print $i
<1.18111300468445>
500338

  DB<106> $i=0; timeit { $i = split /\t1\n/, $l }; print $i
<0.507856845855713>
500339

 DB<122> $i=0; timeit { local $/="\t1\n";open my $D,'<',\$l; $i++ while (<$D>) }; print $i
<0.703027963638306>
500339