Single vs. Double Quotes in PHP Strings: When Should I Use Which?

String Quotation in PHP: Single vs. Double Quotes

In PHP, strings can be enclosed in single or double quotes, offering different functionality and interpretation.

Single-Quoted Strings

Single-quoted strings are interpreted "as is" without any parsing. This means:

• Variables are not expanded.
• Most escape sequences are not recognized.
• Single quotes can be escaped using a backslash (').

However, single-quoted strings are still parsed to interpret the backslash escape sequence ().

Double-Quoted Strings

Double-quoted strings are more dynamic and undergo parsing. Here's what happens:

• Variables within the string are evaluated.
• Escape sequences are interpreted, including those used in regular expressions.
• You can use curly braces ({}) to isolate variable names for evaluation.

Heredoc and Nowdoc Strings

PHP also supports Heredocs and Nowdocs, which allow you to define multiline strings in a readable format:

• Heredoc: Uses <<< followed by an identifier, a newline, the string, and the same identifier again to close it.
• Nowdoc: Similar to heredoc but with an identifier enclosed in single quotes (<<<'EOT').

Heredocs undergo double-quoted string parsing, while Nowdocs are parsed like single-quoted strings (no variable expansion or escape sequence interpretation).

Note:

• Single and double quotes inside single and double-quoted strings must be escaped.
• Performance-wise, there is no significant difference between single-quoted and double-quoted strings.

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