$ perl -MBenchmark=cmpthese -e'my ($foo, $bar); cmpthese(10000000,{ interp => sub{ $foo = qq(gabbit$/)}, concat => sub { $bar = q(gabbit).$/}});'
Benchmark: timing 10000000 iterations of concat, interp...
    concat:  6 wallclock secs ( 4.36 usr +  0.00 sys =  4.36 CPU) @ 2293577.98/s (n=10000000)
    interp:  6 wallclock secs ( 4.60 usr + -0.01 sys =  4.59 CPU) @ 2178649.24/s (n=10000000)
            Rate interp concat
interp 2178649/s     --    -5%
concat 2293578/s     5%     --
$