php7 string escape

In PHP programming, string is one of the common data types. We often need to escape strings to ensure that the code can run normally and avoid potential security risks. As PHP versions are constantly updated, string escaping has also undergone some changes. This article will introduce the string escape operation in PHP7.

1. Escape characters

In PHP, escape characters are used to represent some special characters, such as quotation marks, backslashes, newlines, etc. Common escape characters include:

• ': represents a single quote
• ": represents a double quote
• \: represents a backslash
• : Indicates line feed character
• : Indicates carriage return character
• : Indicates tab character
• : Indicates vertical tab character

in the string The syntax for using escape characters in is as follows:

$string = 'This is a 'string'';
$string = "This is a "string"";
$string = "This is a string with a \ backslash";
$string = "This is a string
with a newline";
$string = "This is a stringwith a carriage return";
$string = "This is a string    with a tab";
$string = "This is a stringwith a vertical tab";

Note that when using a single-quote string, you can only use single-quote escape characters, but not double-quote escape characters. For example:

$string = 'This is a "string"'; // 错误
$string = 'This is a 'string''; // 正确

Double quoted strings can use either double quote escape characters or single quote escape characters.

Before PHP7, in order to avoid unexpected string escape problems, we needed to manually The string is double escaped, that is:

$str = '
'; // 双重转义后的字符串

However, some changes have been made to string escaping in PHP7, and this double escaping method is no longer needed.

2. Modern escape syntax

In PHP7, we can use modern escape syntax to handle string escape. After using modern escape syntax, we do not need to manually double escape escape characters, the code will More clear and concise. Modern escape syntax includes two forms: double-quoted strings and heredoc/nowdoc strings.

1. Modern escape syntax for double-quoted strings

In a double-quoted string, you can use curly braces to enclose the variable name in order to include the value of the variable in the string. Now, we can use the escape character $ in front of the variable name to indicate that it is a variable name.

For example, the following code uses modern double-quote string escape syntax:

$name = 'John';
$string = "Hello, {$name}!";
echo $string; // 输出：'Hello, John!'

In the above code, since we use curly braces {} for variable embedding, we need to use preceded by the escape character $. If we did not use the new escape syntax, the code would need to be double escaped manually:

$name = 'John';
$string = "Hello, {$name}!";
$string = "Hello, ".$name."!";
echo $string; // 输出：'Hello, John!'

2. Modern escape syntax for heredoc/nowdoc strings

heredoc and nowdoc strings were introduced in PHP5.3. The characteristic of these two strings is that they can contain multiple lines of text in the string without escaping.

The heredoc string starts with the <<< operator and ends with the same identifier:

$str = <<<EOD
This is
a
multi-line
string.
EOD;

The nowdoc string starts with a single quote and ends with the same single quote:

$str = <<<'EOD'
This is
a
multi-line
string.
EOD;

In PHP7, we can use modern escape syntax to handle escape characters in heredoc/nowdoc strings. Here is the new syntax:

$str = <<<EOD
This is
a "multi-line" string.
EOD;
echo $str; // 输出：'This is
a "multi-line" string.'

$str = <<<'EOD'
This is
a 'multi-line' string.
EOD;
echo $str; // 输出：'This is
a 'multi-line' string.'

In modern syntax, if we need to include For escape characters, you can use escape characters directly without double escaping.

3. Summary

In PHP7, there have been some changes in the string escape operation. Modern escaping syntax can help us write clearer and more concise code and avoid the tedious process of manual double escaping. If you are a PHP developer, it is recommended that you use modern escape syntax to improve the readability and maintainability of your code.

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