Extract PHP Code with Regular Expressions

Something like this might work

/<\?php.+?\?>$/ms

This pattern uses two flags

• m for PCRE_MULTILINE

  By default, PCRE treats the subject string as consisting of a single "line" of characters (even if it actually contains several newlines). The "start of line" metacharacter (^) matches only at the start of the string, while the "end of line" metacharacter ($) matches only at the end of the string, or before a terminating newline (unless D modifier is set). This is the same as Perl. When this modifier is set, the "start of line" and "end of line" constructs match immediately following or immediately before any newline in the subject string, respectively, as well as at the very start and end. This is equivalent to Perl's /m modifier. If there are no "\n" characters in a subject string, or no occurrences of ^ or $ in a pattern, setting this modifier has no effect.

• s for PCRE_DOTALL

  If this modifier is set, a dot metacharacter in the pattern matches all characters, including newlines. Without it, newlines are excluded. This modifier is equivalent to Perl's /s modifier. A negative class such as [^a] always matches a newline character, independent of the setting of this modifier.

Here's what a couple matches would look like

Caveat it doesn't work if it can't find ?> at the end of a line.

So it works in the case of

• ?>');
• ?> */

But it wouldn't work for

<?php
  echo "actual code";
  /*
   * comment ?>
   */
?>

Story short, if your code is that messy, you need a better solution. If your code is clean, it should work just fine.

You can try with this pattern:

$pattern = <<<'LOD'
~

#definitions
(?(DEFINE)
    (?<sq> '(?:[^'\\]+|\\.)*+' ) # content inside simple quotes
    (?<dq> "(?:[^"\\]+|\\.)*+" ) # content inside double quotes
    (?<vn> [a-zA-Z_]\w*+ ) # variable name
    (?<hndoc> <<< (["']?) (\g<vn>) \g{-2} \R # content inside here/nowdoc
              (?: [^\r\n]+ | \R+ (?!\g{-1}; $) )*+
              \R \g{-1}; \R
    )
    (?<cmt> /\*                      # multiline comments
             (?> [^*]+ | \* (?!/) )*+
             \*/
    )
)

#pattern
<\?php \s+
(?: [^"'?/<]+ | \?+(?!>) | \g<sq> | \g<dq> | \g<hndoc> | \g<cmt> | [</]+ )*+
(?: \?> | \z )

~xsm
LOD;

Test:

$subject = <<<'LOD'
<h1>Extract the PHP Code</h1>
    <?php
        echo(date("F j, Y, g:i a") . ' and a stumbling block: ?>');
        /* Another stumbling block ?> */
        echo <<<'EOD'
    Youpi!!! ?>
EOD;
        echo(' that works.');
    ?>
<p>Some HTML text ...</p>
LOD;

preg_match_all($pattern, $subject, $matches);

print_r($matches);

As mario suggests it in a comment, you can use the tokenizer. It's the most easy way to do that since you don't have to define anything, example:

$tokens = token_get_all($subject);
$display = false;
foreach ($tokens as $token) {
    if (is_array($token)) {
        if ($token[0]==T_OPEN_TAG) $display = true;
        if ($display) echo $token[1];
        if ($token[0]==T_CLOSE_TAG) $display = false;
    } else {
        if ($display) echo $token;
    }
}