A string is a set of characters (letters, numbers and symbols) inside single quotes, e.g. 'This is a string' or double quotes, e.g. "This is a string".

Example code:

$greeting = 'Hello';
$name = 'John';

echo $greeting . ' ' . $name . '!'; // Outputs: Hello John!
echo "$greeting $name!"; // Outputs: Hello John!
echo "{$greeting} $name!"; // Outputs: Hello John!

String Concatenation

The echo $greeting . ' ' . $name . '!'; uses “concatenation” which combines/concatenate string values using the dot operator.

String Interpolation

The echo "$greeting $name!"; uses “interpolation” which expands a variable’s value when wrapped inside double quotes.

The echo "{$greeting} $name!"; uses another form of interpolation that expands a variable’s value inside curly braces that are inside double quotes. This can be useful when prefixing or suffixing a string, for example:

$table_prefix = 'site_';
echo "{$table_prefix}users"; // Outputs: site_users

Escaping Characters

If a string contains quotation marks, enclose it in single quotes or if you want to use double quotes instead, prepend the quotation marks with a backslash, also known as the “escape character”, for example:

echo '"Hello World!"'; // Outputs: "Hello World!"
echo "\"Hello World!\""; // Outputs: "Hello World!"

If a string contains apostrophes, enclose it in double quotes or if you want to use single quotes, prepend the apostrophes with a backslash, for example:

echo "Child's Play"; // Outputs: Child's Play
echo 'Child\'s Play'; // Outputs: Child's Play

Appending Values

You can append values to an existing variable using the dot equals operator like so:

$var = 'Hello';
$var .= ' World';

Or its longer format…

$var = 'Hello';
$var = $var . ' World';

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This is part 4 of the PHP Basics series.