Match strings, allowing for escape characters.

string-regex.md

Regular expression to match either a single or double quoted string, taking into account escape characters: /(["'])((?:(?!\1|\\).|\\.)*?)\1/

It's recommended that you remove escape characters from the resulting string (replace \\((?=\%s|\\).) with \1 substituting %s for the matched quote character):

preg_match('/(["\'])((?:(?!\\1|\\\\).|\\\\.)*?)\\1/', $string, $matches);
$extractedStringValue = preg_replace(sprintf('/\\\\((?=\\\\|\\%s).)/', $matches[1]), '\1', $matches[2]);

Examples

String	Match?	Group 1	Group 2	With Escape Char Removal
'This is a string'	Yes	'	This is a string	This is a string
"This is a string"	Yes	"	This is a string	This is a string
"This is a string'	No	"
"This is a string\"	No	"
"This is a string\\"	Yes	"	This is a string\\	This is a string\
"This is a string\""	Yes	"	This is a string\"	This is a string"
"This is a string\\\"	No	"
"This is a string\\\""	Yes	"	This is a string\\\"	This is a string\"
This "is a" string	Yes	"	is a	is a
This 'is \a' string	Yes	'	is \a	is \a
This 'is \\a' string	Yes	'	is \\a	is \a
"This \\\"is a\" string"	Yes	"	This \\\"is a\" string	This \"is a" string
"This \\\"is a\\" string"	Yes	"	This \\\"is a\\	This \"is a\

Escape Char Removal Examples

Before	After
\	\
\\	\
\\"	\"
\\\"	\"