Please don't use sprintf...

benchmark.php

<?php

$maxiter = 10000000;
$value = "1234";

$time_start = microtime(true);

for ($i = 0; $i < $maxiter; ++$i) {
    $string = "This is " . $value;
}

$time_end = microtime(true);
$time = $time_end - $time_start;

echo "concatenate in $time seconds\n";

$time_start = microtime(true);

for ($i = 0; $i < $maxiter; ++$i) {
    $string = "This is {$value}";
}

$time_end = microtime(true);
$time = $time_end - $time_start;

echo "interpolated in $time seconds\n";

$time_start = microtime(true);

for ($i = 0; $i < $maxiter; ++$i) {
    $string = sprintf('This is %s', $value);
}

$time_end = microtime(true);
$time = $time_end - $time_start;

echo "sprintf in $time seconds\n";