> perl bench_regexp 100000lines.92MB.file 
Benchmark: timing 1 iterations of 2_grep_string, 4_grep_string, four_string, one_string, two_string...
Matched records: 1
2_grep_string:  3 wallclock secs ( 2.91 usr +  0.44 sys =  3.35 CPU) @  0.30/s (n=1)
            (warning: too few iterations for a reliable count)
Matched records: 1
4_grep_string:  4 wallclock secs ( 3.56 usr +  0.42 sys =  3.98 CPU) @  0.25/s (n=1)
            (warning: too few iterations for a reliable count)
Matched records: 1
four_string: 100 wallclock secs (98.83 usr +  0.56 sys = 99.39 CPU) @  0.01/s (n=1)
            (warning: too few iterations for a reliable count)
Matched records: 1
one_string:  2 wallclock secs ( 1.62 usr +  0.40 sys =  2.02 CPU) @  0.50/s (n=1)
            (warning: too few iterations for a reliable count)
Matched records: 1
two_string: 75 wallclock secs (73.87 usr +  0.53 sys = 74.40 CPU) @  0.01/s (n=1)
            (warning: too few iterations for a reliable count)