PHP - preg_match/preg_replace problems

Question

I'm a little confused with preg_match and preg_replace. I have a very long content string (from a blog), and I want to find, separate and replace all [caption] tags. Possible tags can be:

[caption]test[/caption]
[caption align="center" caption="test" width="123"]<img src="...">[/caption]
[caption caption="test" align="center" width="123"]<img src="...">[/caption]

etc.

Here's the code I have (but I'm finding that's it not working the way I want it to...):

public function parse_captions($content) {
    if(preg_match("/\[caption(.*) align=\"(.*)\" width=\"(.*)\" caption=\"(.*)\"\](.*)\[\/caption\]/", $content, $c)) {
        $caption = $c[4];         
        $code = "<div>Test<p class='caption-text'>" . $caption . "</p></div>";
        // Here, I'd like to ONLY replace what was found above (since there can be
        // multiple instances
        $content = preg_replace("/\[caption(.*) width=\"(.*)\" caption=\"(.*)\"\](.*)\[\/caption\]/", $code, $content);
    }
    return $content;
}

Casimir et Hippolyte · Accepted Answer · 2013-06-09 04:35:59Z

The goal is to ignore the content position. You can try this:

$subject = <<<'LOD'
[caption]test1[/caption]
[caption align="center" caption="test2" width="123"][/caption]
[caption caption="test3" align="center" width="123"][/caption]
LOD;

$pattern = <<<'LOD'
~
\[caption                          # begining of the tag 
(?>[^]c]++|c(?!aption\b))*         # followed by anything but c and ]
                                   # or c not followed by "aption"

(?|                                # alternation group
    caption="([^"]++)"[^]]*+]      # the content is inside the begining tag  
  |                                # OR
    ]([^[]+)                       # outside 
)                                  # end of alternation group

\[/caption]                        # closing tag
~x
LOD;

$replacement = "<div>Test<p class='caption-text'>$1</p></div>";

echo htmlspecialchars(preg_replace($pattern, $replacement, $subject));

pattern (condensed version):

$pattern = '~\[caption(?>[^]c]++|c(?!aption\b))*(?|caption="([^"]++)"[^]]*+]|]([^[]++))\[/caption]~';

pattern explanation:

After the begining of the tag you could have content before ] or the caption attribute. This content is describe with:

(?>                # atomic group
    [^]c]++        # all characters that are not ] or c, 1 or more times
  |                # OR
    c(?!aption\b)  # c not followed by aption (to avoid the caption attribute)
)*                 # zero or more times

The alternation group (?| allow multiple capture groups with the same number:

(?|
       # case: the target is in the caption attribute #
    caption="      # (you can replace it by caption\s*+=\s*+")
    ([^"]++)       # all that is not a " one or more times (capture group)
    "
    [^]]*+         # all that is not a ] zero or more times

  |           # OR

       # case: the target is outside the opening tag #
    ]              # square bracket close the opening tag
    ([^[]+)        # all that is not a [ 1 or more times (capture group)
)

The two captures have now the same number #1

Note: if you are sure that each caption tags aren't on several lines, you can add the m modifier at the end of the pattern.

Note2: all quantifiers are possessive and i use atomic groups when it's possible for quick fails and better performances.

hjpotter92 · Accepted Answer · 2013-06-09 01:59:02Z

0

Hint (and not an answer, per se)

Your best method of action would be:

Match everything after caption.

preg_match("#\[caption(.*?)\]#", $q, $match)

Use an explode function for extracting values in $match[1], if any.
```
explode(' ', trim($match[1]))
```
Check the values in array returned, and use in your code accordingly.

answered Jun 9, 2013 at 1:59

hjpotter92

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