I think that for the index case the situation is not so clear. Both the regex engine and index() will use the same Boyer-Moore routine and for me personally, the regex version is more readable. But as always, YMMV.
use Benchmark qw(:all) ;
my $value = 'FALSE';
my $count = 1_000_000;
cmpthese($count, {
'regex' => sub { $value =~ /^true$/i },
'eq' => sub { lc $value eq "true" },
'index' => sub { index( lc $value, "true" ) >= 0 },
});
yields
Benchmark: timing 1000000 iterations of eq, index, regex...
eq: 1 wallclock secs ( 0.89 usr + 0.00 sys = 0.89 CPU) @ 11
+23595.51/s (n=1000000)
index: 2 wallclock secs ( 1.65 usr + 0.00 sys = 1.65 CPU) @ 60
+6060.61/s (n=1000000)
regex: 2 wallclock secs ( 1.63 usr + 0.00 sys = 1.63 CPU) @ 61
+3496.93/s (n=1000000)
Rate index regex eq
index 606061/s -- -1% -46%
regex 613497/s 1% -- -45%
eq 1123596/s 85% 83% --
Update: As AM has pointed out (thank you!), the benchmark above has a bug. Using the tests
'regex' => sub { $value =~ /true/i },
'regex_anch' => sub { $value =~ /^true$/i },
'eq' => sub { lc $value eq "true" },
'index' => sub { index( lc $value, "true" ) >= 0 },
I get the results
Benchmark: timing 1000000 iterations of eq, index, regex, regex_anch..
+.
eq: 1 wallclock secs ( 0.88 usr + 0.00 sys = 0.88 CPU) @ 11
+36363.64/s (n=1000000)
index: 0 wallclock secs ( 1.65 usr + 0.00 sys = 1.65 CPU) @ 60
+6060.61/s (n=1000000)
regex: 0 wallclock secs ( 1.08 usr + 0.00 sys = 1.08 CPU) @ 92
+5925.93/s (n=1000000)
regex_anch: 2 wallclock secs ( 1.59 usr + 0.00 sys = 1.59 CPU) @ 62
+8930.82/s (n=1000000)
Rate index regex_anch regex eq
index 606061/s -- -4% -35% -47%
regex_anch 628931/s 4% -- -32% -45%
regex 925926/s 53% 47% -- -19%
eq 1136364/s 87% 81% 23% --
with the surprising result that the regex w/o the anchor is
faster than the anchored version. Multiple runs yield similar results. As the AM says, one could try many different regex-value combos, but I expect the results to be not far different, precisely because both index and regex engine use the same BM function.