$var = "foo" ;
    $var .= "bar" ;             # 1

    $var = "foo$var" ;          # 2

    substr($var,0,0) = "foo" ;  # 3

##</code><code>##

#!/usr/bin/perl -w

use Benchmark;

timethese(1_500_000, {
    Interpolate => q/$var = "String"; $var = "foo$var";/,
    Concatenate => q/$var = "String"; $var = "foo" . $var;/,
    Substr      => q/$var = "String"; substr($var, 0, 0) = 'foo'/
});

##</code><code>##

Benchmark: timing 1500000 iterations of Concatenate, Interpolate, Substr...
Concatenate:  1 wallclock secs ( 1.56 usr +  0.00 sys =  1.56 CPU) @ 960000.00/s (n=1500000)
Interpolate:  1 wallclock secs ( 1.59 usr +  0.00 sys =  1.59 CPU) @ 945812.81/s (n=1500000)
    Substr:  2 wallclock secs ( 2.07 usr +  0.01 sys =  2.08 CPU) @ 721804.51/s (n=1500000)