a.php

<?php

$st = microtime(true);
for($i = 0; $i < 100000000; $i++)
    echo 'testabcdeftestabcdeftestabcdeftestabcdeftestabcdeftest';
$sm = microtime(true);
fwrite(STDERR, "single quote" . "\t" . ($sm - $st) . "\n");

$st = microtime(true);
for($i = 0; $i < 100000000; $i++)
    echo "testabcdeftestabcdeftestabcdeftestabcdeftestabcdeftest";
$sm = microtime(true);
fwrite(STDERR, "double quote" . "\t" . ($sm - $st) . "\n");


$test = "abcdef";

$st = microtime(true);
for($i = 0; $i < 10000000; $i++)
    echo 'test' . $test . 'test' . $test . 'test' . $test . 'test' . $test . 'test' . $test . 'test';
$sm = microtime(true);
fwrite(STDERR, "single quote, dot" . "\t" . ($sm - $st) . "\n");

$st = microtime(true);
for($i = 0; $i < 10000000; $i++)
    echo "test" . $test . "test" . $test . "test" . $test . "test" . $test . "test" . $test . "test";
$sm = microtime(true);
fwrite(STDERR, "double quote, dot" . "\t" . ($sm - $st) . "\n");

$st = microtime(true);
for($i = 0; $i < 10000000; $i++)
    echo "test", $test, "test", $test, "test", $test, "test", $test, "test", $test, "test";
$sm = microtime(true);
fwrite(STDERR, "double quote, comma" . "\t" . ($sm - $st) . "\n");

$st = microtime(true);
for($i = 0; $i < 10000000; $i++)
    echo "test${test}test${test}test${test}test${test}test${test}test";
$sm = microtime(true);
fwrite(STDERR, "double quote, \${i}" . "\t" . ($sm - $st) . "\n");

$st = microtime(true);
for($i = 0; $i < 10000000; $i++)
    echo "test{$test}test{$test}test{$test}test{$test}test{$test}test";
$sm = microtime(true);
fwrite(STDERR, "double quote, {\$i}" . "\t" . ($sm - $st) . "\n");

$st = microtime(true);
for($i = 0; $i < 10000000; $i++)
    echo "test$test test$test test$test test$test test$test test";
$sm = microtime(true);
fwrite(STDERR, "double quote, \$i" . "\t" . ($sm - $st) . "\n");