What is the difference between php double quotation marks and single quotation marks

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Description

1. Double quotation marks explain variables, while single quotation marks do not explain variables.

2. Insert single quotation marks in double quotation marks. If there is a variable in single quotation marks, then explain the variable.

3. The double quotation mark variable name must be followed by a non-numeric number.

Letters, special underlined characters, or enclose variables in {}, otherwise the following part of the variable name will be taken as a whole, resulting in syntax errors.

4. the efficiency of single quotation marks is higher than that of double quotation marks.

You can make single quote characters use single quotation marks as much as possible.

Example

$echo 'single quotation marks:'. $r.'

'; $r = str_replace ("\ t",',', $s); echo 'double quotes:' .$ r.'

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