$re = '/\s* # white spaces
########################## KEYS START ##########################
(?: # We\'ll use this to make keys optional
(?P<keys> # named group: keys
\d+ # match digits
| # or
"(?(?=\\\\\\\\")..|[^"])*" # match string between "", works even 4 escaped ones "hello \" world"
| # or
\'(?(?=\\\\\\\\\')..|[^\'])*\' # match string between \'\', same as above :p
| # or
\$\w+(?:\[(?:[^[\]]|(?R))*\])* # match variables $_POST, $var, $var["foo"], $var["foo"]["bar"], $foo[$bar["fail"]]
) # close group: keys
########################## KEYS END ##########################
\s* # white spaces
=> # match =>
)? # make keys optional
\s* # white spaces
########################## VALUES START ##########################
(?P<values> # named group: values
\d+ # match digits
| # or
"(?(?=\\\\\\\\")..|[^"])*" # match string between "", works even 4 escaped ones "hello \" world"
| # or
\'(?(?=\\\\\\\\\')..|[^\'])*\' # match string between \'\', same as above :p
| # or
\$\w+(?:\[(?:[^[\]]|(?R))*\])* # match variables $_POST, $var, $var["foo"], $var["foo"]["bar"], $foo[$bar["fail"]]
| # or
array\s*\((?:[^()]|(?R))*\) # match an array()
| # or
\[(?:[^[\]]|(?R))*\] # match an array, new PHP array syntax: [1, 3, 5] is the same as array(1,3,5)
| # or
(?:function\s+)?\w+\s* # match functions: helloWorld, function name
(?:\((?:[^()]|(?R))*\)) # match function parameters (wut), (), (array(1,2,4))
(?:(?:\s*use\s*\((?:[^()]|(?R))*\)\s*)? # match use(&$var), use($foo, $bar) (optionally)
\{(?:[^{}]|(?R))*\} # match { whatever}
)?;? # match ; (optionally)
) # close group: values
########################## VALUES END ##########################
\s* # white spaces/xsi';
$str = '\'key1\', \'key2\'';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php