The usage analysis of PHP double quotation mark and single quotation mark

This article share, I encountered in the actual work of PHP double quotation marks and single quotation marks of a problem, and with the solution, the need for friends, can make a reference. Using PHP to filter line breaks in strings is typically done: PHP provides three ways to define strings: single quotes, double quotes, local documents (in English called here Document or Heredoc). Single quotes: Using single quotation marks is the most efficient method, because PHP does not check for built-in variables and escape sequences in single-quote strings, only the backslash and the single quotation mark itself that need to be escaped. Double quotes: The built-in variables and escape sequences are checked, but escaped single quotes are not recognized. This also illustrates the mistake of starting that code by using double quotation marks to define the escape sequence of the newline: Check all built-in variables and escape sequences, with double quotes without escaping. For example:

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