There are several types of string variables declared in php

In PHP, there are three ways to declare string variables: using single quotes, using double quotes, and using heredoc and nowdoc.

1. Single quotes: Variables in single-quoted strings will not be parsed, and all special characters (such as newlines and quotes) need to use the escape symbol "\".

$name = 'John';
echo 'Hello, my name is ' . $name . '!';  // 输出：Hello, my name is John!

2. Double quotation marks: Double quotation mark strings can parse variables and special characters. When using, just include the variables directly in double quotation marks.

$name = 'John';
echo "Hello, my name is $name!";  // 输出：Hello, my name is John!

3. Heredoc: Similar to double-quoted strings, but using heredoc syntax to make the code clearer and more readable.

$name = 'John';
$heredocStr = <<<EOD
    Hello, my name is $name!
    This is a multi-line string.
EOD;
echo $heredocStr;  // 输出：Hello, my name is John! This is a multi-line string.

4. Nowdoc: Similar to a single-quoted string, but variables in the nowdoc string will not be parsed.

$name = 'John';
$nowdocStr = <<<'EOD'
    Hello, my name is $name!
    This is a multi-line string.
EOD;
echo $nowdocStr;  // 输出：Hello, my name is $name! This is a multi-line string.

The above are the three ways to declare string variables in PHP. By declaring string variables in different ways, you can make the code clearer and easier to read, and you can choose the most suitable way according to your specific needs.

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