Extracting some content from given string - php

Question

This is the content piece:
This is content that is a sample.
[md] Special Content Piece [/md]
This is some more content.
What I want is a preg_match_all expression such that it can fetch and give me the following from the above content:
[md] Special Content Piece [/md]
I have tried this:
$pattern ="/\[^[a-zA-Z][0-9\-\_\](.*?)\[\/^[a-zA-Z][0-9\-\_]\]/";
preg_match_all($pattern, $content, $matches);
But it gives a blank array. Could someone help?

Answer 1

$pattern = "/\[md\](.*?)\[\md\]/";
generally
$pattern = "/\[[a-zA-Z0-9\-\_]+\](.*?)\[\/[a-zA-Z0-9\-\_]+\]/";
or even better
$pattern = "/\[\w+\](.*?)\[\/\w+\]/";
and to match the start tag with the end tag:
$pattern = "/\[(\w+)\](.*?)\[\/\1\]/";
(Just note that the "tag" name is then returned in the match array.)

Answer 2

You can use this:
$pattern = '~\[([^]]++)]\K[^[]++(?=\[/\1])~';
explanation:
~ #delimiter of the pattern
\[ #literal opening square bracket (must be escaped)
( #open the capture group 1
[^]]++ #all characters that are not ] one or more times
) #close the capture group 1
] #literal closing square bracket (no need to escape)
\K #reset all the match before
[^[]++ #all characters that are not [ one or more times
(?= #open a lookahead assertion (this doesn't consume characters)
\[/ #literal opening square bracket and slash
\1 #back reference to the group 1
] #literal closing square bracket
) #close the lookhead
~
Interest of this pattern:
The result is the whole match because i have reset all the match before \K and because the lookahead assertion, after what you are looking for, don't consume characters and is not in the match.
The character classes are defined in negative and therefore are shorter to write and permissive (you don't care about what characters must be inside)
The pattern checks if the opening and closing tags are the same with the system of capture group\back reference.
Limits:
This expression don't deal with nested structures (you don't ask for). If you need that, please edit your question.
For nested structures you can use:
(?=(\[([^]]++)](?<content>(?>[^][]++|(?1))*)\[/\2]))
If attributes are allowed in your bbcode:
(?=(\[([^]\s]++)[^]]*+](?<content>(?>[^][]++|(?1))*)\[/\2]))
If self-closing bbcode tags are allowed:
(?=((?:\[([^][]++)](?<content>(?>[^][]++|(?1))*)\[/\2])|\[[^/][^]]*+]))
Notes:
A lookahead means in other words: "followed by"
I use possessive quantifiers (++) instead of simple gready quantifiers (+) to inform the regex engine that it doesn't need to backtrack (gain of performance) and atomic groups (ie:(?>..)) for the same reasons.
In the patterns for nested structures slashes are not escaped, to use them you must choose a delimiter that is not a slash (~, #, `).
The patterns for nested structures use recursion (ie (?1)), you can have more informations about this feature here and here.

Answer 3

Update:
If you're likely to be working with nested "tags", I'd probably go for something like this:
$pattern = '/(\[\s*([^\]]++)\s*\])(?=(.*?)(\[\s*\/\s*\2\s*\]))/';
Which, as you probably can tell, is not unlike what CasimiretHippolyte suggested (only his regex, AFAIKT, won't capture outer tags in a scenario like the following:)
his is content that is a sample.
[md] Special Content [foo]Piece[/foo] [/md]
This is some more content.
Whereas, with this expression, $matches looks like:
array (
0 =>
array (
0 => '[md]',
1 => '[foo]',
),
1 =>
array (
0 => '[md]',
1 => '[foo]',
),
2 =>
array (
0 => 'md',
1 => 'foo',
),
3 =>
array (
0 => ' Special Content [foo]Piece[/foo] ',
1 => 'Piece',
),
4 =>
array (
0 => '[/md]',
1 => '[/foo]',
),
)
A rather simple pattern to match all substrings looking like this [foo]sometext[/foo]
$pattern = '/(\[[^\/\]]+\])([^\]]+)(\[\s*\/\s*[^\]]+\])/';
if (preg_match_all($pattern, $content, $matches))
{
echo '<pre>';
print_r($matches);
echo '</pre>';
}
Output:
array (
0 =>
array (
0 => '[md] Special Content Piece [/md]',
),
1 =>
array (
0 => '[md]',
),
2 =>
array (
0 => ' Special Content Piece ',
),
3 =>
array (
0 => '[/md]',
),
)
How this pattern works: It's devided into three groups.
The first: (\[[^\/\]]+\]) matches opening and closing [], with everything inbetween that is neither a closing bracket nor a forward slash.
The second: '([^]]+)' matches every char after the first group that is not [
The third: (\[\s*\/\s*[^\]]+\]) matches an opening [, followed by zero or more spaces, a forward slash, again followed by zero or more spaces, and any other char that isn't ]
If you want to match a specific end-tag, but keeping the same three groups (with a fourth), use this (slightly more complex) expression:
$pattern = '/(\[\s*([^\]]+?)\s*\])(.+?)(\[\s*\/\s*\2\s*\])/';
This'll return:
array (
0 =>
array (
0 => '[md] Special Content Piece [/md]',
),
1 =>
array (
0 => '[md]',
),
2 =>
array (
0 => 'md',
),
3 =>
array (
0 => ' Special Content Piece ',
),
4 =>
array (
0 => '[/md]',
),
)
Note that group 2 (the one we used in the expression as \2) is the "tagname" itself.