perl -MBenchmark -e 'timethese( 1000, 
  { cat => sub { my $str = qx|cat /usr/share/dict/words|; }, 
read => sub { local $/; open my $f, "/usr/share/dict/words" 
or die $!; my $str = <$f>; } } )'
Benchmark: timing 1000 iterations of cat, read...
  cat:  6 wallclock secs ( 1.69 usr  1.34 sys +  0.28 cusr  
2.34 csys =  5.65 CPU) @ 330.03/s (n=1000)
  read:  1 wallclock secs ( 0.58 usr +  0.58 sys =  1.16 
CPU) @ 862.07/s (n=1000)