sub two_pass {
    my @matched;
    open (my $FH, "<$file");
    while (my $rec = <$FH>) {
        if ( $rec =~ '500_000' ) {
                push @matched, $rec;
        }
        if ( $rec =~ '500_001' ) {
                push @matched, $rec;
        }
    }
    print "two pass: " . @matched;
    close $FH;
}

##</code><code>##

c:\test>junk31 836952.log
Benchmark:
timing 1 iterations of
 AAtwo_pass, BBtwo_string, CCone_string
...

two pass: 10
AAtwo_pass:  6 wallclock secs ( 5.69 usr +  0.78 sys =  6.47 CPU) @  0.15/s (n=1)

            (warning: too few iterations for a reliable count)

two string: 10
BBtwo_string: 15 wallclock secs (14.34 usr +  0.73 sys = 15.07 CPU) @  0.07/s (n=1)

            (warning: too few iterations for a reliable count)

one string: 7
CCone_string: 15 wallclock secs (14.76 usr +  0.76 sys = 15.52 CPU) @  0.06/s (n=1)

            (warning: too few iterations for a reliable count)

##</code><code>##

c:\test>\perl32\bin\perl junk31.pl 836952.log
Benchmark:
timing 1 iterations of
 AAtwo_pass, BBtwo_string, CCone_string
...

two pass: 10
AAtwo_pass:  8 wallclock secs ( 6.60 usr +  0.69 sys =  7.29 CPU) @  0.14/s (n=1)

            (warning: too few iterations for a reliable count)

two string: 10
BBtwo_string: 53 wallclock secs (52.99 usr +  0.70 sys = 53.70 CPU) @  0.02/s (n=1)

            (warning: too few iterations for a reliable count)

one string: 7
CCone_string:  7 wallclock secs ( 5.60 usr +  0.92 sys =  6.52 CPU) @  0.15/s (n=1)

            (warning: too few iterations for a reliable count)