The difference between single and double quotes in php

phpThe difference between single and double quotes

phpThe difference between single quotes and double quotes:

The content in the double-quote string can be interpreted and replaced, while the content in the single-quote string is always considered to be ordinary characters.

For example:

$foo = 2; 
echo "foo is $foo"; // 打印结果: foo is 2 
echo 'foo is $foo'; // 打印结果: foo is $foo 
echo "foo is $foo\n"; // 打印结果: foo is 2 (同时换行) 
echo 'foo is $foo\n'; // 打印结果: foo is $foo\n 
$foo = 2; 
echo "foo is $foo"; // 打印结果: foo is 2 
echo 'foo is $foo'; // 打印结果: foo is $foo 
echo "foo is $foo\n"; // 打印结果: foo is 2 (同时换行) 
echo 'foo is $foo\n'; // 打印结果: foo is $foo\n 　

Even the backslash in a single quote string loses its extended meaning (except for the insertion of backslash \\ and the insertion of single quote \'). Therefore, when you want to perform variable substitution and include escape sequences such as \n (newline character) in a string, you should use double quotes. Single quoted strings can be used anywhere else, and scripts will process faster if single quoted strings are used.

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