Programming PHP, 3rd Edition

Printing Strings

There are four ways to send output to the browser. The echo construct lets you print many values at once, while print() prints only one value. The printf() function builds a formatted string by inserting values into a template. The print_r() function is useful for debugging—it prints the contents of arrays, objects, and other things, in a more-or-less human-readable form.

echo

To put a string into the HTML of a PHP-generated page, use echo. While it looks—and for the most part behaves—like a function, echo is a language construct. This means that you can omit the parentheses, so the following are equivalent:

echo "Printy";
echo("Printy"); // also valid

You can specify multiple items to print by separating them with commas:

echo "First", "second", "third";
Firstsecondthird

It is a parse error to use parentheses when trying to echo multiple values:

// this is a parse error
echo("Hello", "world");

Because echo is not a true function, you can’t use it as part of a larger expression:

// parse error
if (echo("test")) {
  echo("It worked!");
}

Such errors are easily remedied, by using the print() or printf() functions.

print()

The print() construct sends one value (its argument) to the browser:

if (print("test\n")) {
  print("It worked!");
}
test
It worked!

printf()

The printf() function outputs a string built by substituting values into a template (the format string). It is derived from the function of the same name in the standard C library. The first argument to printf() is the format ...