The most basic form of string usage is with single quotes. Everything within the single quotes is taken as a literal. Unlike other forms of quoting, which will substitute values for variable names within a string, this scheme stores a string exactly as it is entered. Let's take a look at this basic example:
<?php $mystring = 'Hello!'; ?>
This assigns the literal string 'Hello!' to the variable '$mystring'. This is about as simple as it gets. As we mentioned a moment ago, this way of quoting does not provide variable substitution. Everything is taken as a literal. To illustrate this point, take a look at the following example.
$mystring = '$var = 1;';
This assignment would result in a string being stored in the variable $mystring just as you see it above. When we cover the double quote technique in a moment, you will see how variable substitution works.
Continuing on with single quotes, if we want to add newlines to our string we can easily just span the string over multiple lines:
<?php $mystring = 'This is the first line, and this is the second.'; ?>
This is the only method that will work for adding newlines to a single quoted string. Attempting to include the escape sequence for a newline, as with the following example, will not work.
<?php //this will not add a newline to the string $mystring = 'First line\nSecond line'; ?>
If we would like to include the literal single quote character within our string, we need to escape it. Within single quotes, the only character that needs to be escaped is the literal single quote character. The one exception to this rule is for the character used to do the escaping, the backslash. If you need a backslash to appear before a single quote, or at the end of a string, you will need to double it. Examples of escaping a single quote and using backslashes are seen below. :
<?php $mystring = 'That\'s too bad.'; $anotherstring = 'This string has a backslash at the end \\'; $andanother = 'A backslash before the single quote: That\\'s to bad.'; ?>
Using single quotes is the most efficient method of dealing with strings because no variable substitution takes place. The speed increase won't be awesome, but every little helps. If you are using very few strings, the difference will barely be measurable. The efficiency gains really don't come into place until you are dealing with a large amount of strings.
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