Your First PHP Script

Every PHP file starts by raising a hand: "PHP code starts here." Everything after that is instructions.

In Setting Up, you installed PHP and ran a small script. Now let's slow down, write one from scratch, and understand every character in it.

Here's the most famous first program in any language, written in PHP:

<?php
echo "Hello, world!\n";

Hello, world!

Two lines. Let's take them apart.

Raising your hand: <?php

Picture a classroom where the teacher is reading a story aloud. Whenever a student raises their hand, the teacher stops and listens to them instead. When the student lowers their hand, the story carries on.

A PHP file works like that. PHP reads the file from top to bottom, and everything is ordinary text to be sent out as it is, until it reaches <?php. That's the raised hand: "PHP instructions start here."

• <?php starts PHP mode. It must be written exactly like that, with no space between <? and php.
• ?> ends PHP mode, and goes back to sending text as it is.

That switching back and forth is the heart of Mixing PHP and HTML, coming up next. In a file that's only PHP, like the ones in this lesson, you leave out the closing ?> altogether. It's the recommended style, since it avoids accidentally sending stray blank lines after it.

echo: send out some text

echo "Hello, world!\n";

• echo sends text out: to the terminal when you run php index.php, or into the page when a browser visits.
• "Hello, world!\n" is the text to send, called a string.
• The semicolon ; ends the statement, like a period ends a sentence. Every PHP statement needs one.

You can echo several things at once, separated by commas, and they're sent one after another with nothing in between:

<?php
echo "Hello", ", ", "world", "!\n";

Hello, world!

New lines: \n

echo doesn't start a new line on its own. Two echos send their text right next to each other:

<?php
echo "First";
echo "Second";

FirstSecond

To start a new line in the terminal, put \n inside the string where you want the line to break. That backslash pair is called an escape sequence: the backslash means "the next character is special." Some useful ones:

Write	To get
\n	a new line
\t	a tab
\"	a double quote inside a double-quoted string
\\	a backslash itself

When PHP builds a web page instead of printing in the terminal, \n only breaks the line in the HTML source. The browser treats it like a space, so for a visible line break on the page, you'd use HTML, like <br> or a new <p>.

Single and double quotes

PHP accepts strings in single or double quotes, but they don't behave the same:

<?php
$name = "Maria";
echo "Hello, $name!\n";
echo 'Hello, $name!\n';

Hello, Maria!
Hello, $name!\n

• In double quotes, PHP looks inside the string: variables like $name are replaced by their values, and escape sequences like \n become new lines. This is called interpolation.
• In single quotes, what you see is what you get: $name and \n are just ordinary characters.

($name = "Maria"; stores a value in a variable. Every PHP variable name starts with $. You'll learn all about them in Variables and Constants.)

Use double quotes when you want a variable or \n inside, and single quotes for plain, fixed text. A handy side effect: an apostrophe is fine inside double quotes, and a double quote is fine inside single quotes:

<?php
echo "It's a sunny day.\n";
echo 'She said "hi" to me.';

It's a sunny day.
She said "hi" to me.

Comments

PHP ignores comments completely. There are three ways to write them:

<?php
// A one-line comment.
# Another way to write a one-line comment.

/*
	A comment that
	spans several lines.
*/
echo "Only this line does anything.\n";

Only this line does anything.

// is the most common for short notes. Use comments to explain why your code does something, not to repeat what it obviously does.

Capital letters

PHP is a little unusual here. Its keywords, like echo, don't care about capital letters, so Echo and ECHO both work. But variable names do: $name and $Name are two different variables. Always write keywords in lowercase, and keep your variable names exactly consistent.

<?php
$name = "Maria";
echo $Name;

Warning: Undefined variable $Name in C:\Users\maria\php-practice\index.php on line 3

PHP printed a warning instead of the name, because $Name with a capital N was never created. The file name in the message will be wherever your own file is saved.

The mistakes everyone makes

Here are the errors almost every beginner hits in their first week.

A missing semicolon.

<?php
echo "Hello, world!"
echo "Bye";
// error: Parse error: syntax error, unexpected token "echo", expecting "," or ";"

PHP expected a ; (or a comma) to end the first statement, and found the next echo instead. Notice that the error points to line 3, the line after the missing semicolon, because that's where PHP realized something was wrong. When an error doesn't make sense on its line, check the line above.

A missing closing quote.

<?php
echo "Hello, world!;
// error: Parse error: syntax error, unexpected end of file

PHP kept reading the string to the end of the file, looking for the closing ". The rest of the message is confusing, but "unexpected end of file" is the clue: something was opened and never closed.

A space inside the tag. <? php with a space isn't a PHP tag, so PHP doesn't recognize the code at all, and sends it out as plain text instead of running it.

A parse error means PHP couldn't even read your file, so nothing in it runs. A warning, like the undefined variable above, means PHP carried on, but something probably isn't right. Take both seriously.

Try it

This script prints a small student ID card. Predict exactly what it prints, including where each line breaks.

Running PHP here

Running PHP right in the browser is coming to Syntaxia soon. For now, you can read and edit the code here. If you have PHP installed on your computer (see Setting Up), save it as index.php and run it with php index.php.

Check your prediction

=== STUDENT ID ===
Name: Maria Santos
Grade: $grade
Grade: 11
Motto: "Measure twice, cut once."
Clubs: Chess & Robotics
==================

The single-quoted 'Grade: $grade' doesn't replace the variable, so it's printed literally. The next line gets it right by passing $grade as a separate item. And Clubs: has no \n, so the next echo continues on the same line.

Try it yourself

1. Change the name and grade to your own, and add a line that prints your favorite subject.
2. Remove the semicolon from any line and run the script. Which line does the error point to?
3. Rewrite the single-quoted Grade line so it prints the actual grade, using double quotes.

Check your understanding

What does echo 'Hi $name'; print, if $name is Ben?

Hi $name

Hi Ben

An error

Hi

How do you end a statement in PHP?

With a new line

With a period

With a semicolon

With a colon

Why leave out the closing ?> in a file that is only PHP?

It makes PHP faster

Closing tags are not allowed in PHP 8

It is required for echo to work

To avoid accidentally sending stray blank lines or spaces after it

Up next

You can switch into PHP and send out text. Next comes PHP's most famous trick: putting it right in the middle of an HTML page, in Mixing PHP and HTML.