regex - regular expression search in php

Solution:

Don't try to match everything at once. Match each link individually then iterate over the results. Usepreg_match_all for this, orpreg_replace_callback if you want to do replace on each match. Using:

a\[(\w+)\]
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should achieve your goal.

It was unclear what the[\s+]? goal was, that optionally would allow whitespaces or+s. Also unclear about the optional comma and space after the links. Keeping it simple is the best approach.

https://3v4l.org/2AvT1

Solution:

With php you can use the\G anchor and then use 2 capture groups to know the difference between the lines at the beginning and the other links.

\Ga\h*\[([^][]*)],?\h*\[([^][]*)]
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Explanation

• \G Assert the current position at the start of the string, or at the end of the previous match
• a\h* Matcha and optional horizontal whitespace chars
• \[([^][]*)] Match[...] and capture in group 1 what is in between the square brackets
• ,?\h* match an optional comma and horizontal whitespace chars
• Or
• \[([^][]*)] Match[...] and capture in group 2 what is in between the square brackets

See a regex demo.

Solution:

I will try now to give an illustrative example of what is needed: There is such a text

a[link1], a[link2] a[link3] text text text a[link4] text a[link5] text

in this text there are links designated a[ ] in the future I need to replace these links and bring it to this form

<a href="link1" class="style1">link1</a><a href="link2" class="style1">link2</a><a href="link3" class="style1">link3</a> text text text <a href="link4" class="style2">link4</a> text <a href="link5" class="style2">link5</a> text

The first three links have a class assigned with the value style1 the links that come after the text already have a class value assigned to style2 At the very beginning, there can be three links before the text, four or even one, as well as after the text there can be any number of links in any order.

Solution:

Thank you all so much for your help. I kind of figured it out. First, I use regular expressions to search for all the links at the beginning of the text, then I run the result through str_replace and change a[ ] to what I need, and at the end I just glue the result through concatenation and output it to the screen.

Solution:

Usepreg_replace_callback() to capture and replace the desired strings in one consolidated process.

Use a lookbehind containing a closing square brace in the first capture group to differentiate between the first match of a continuous series versus a subsequent member of the same continuous series.

The first capture group ($m[1]) will be null or an empty string

The second capture group ($m[2]) will be the glue characters between continuous links.
The third capture group ($m[3]) will be the link's targeted text.

Every time you encounter a first-in-group link (null lookbehind), increment the style counter.

Code: (Demo)

$styleCounter = 0;
echo preg_replace_callback(
         '/((?<=]))?+(,? ?)a\[([^][]*)]/',
         function ($m) use(&$styleCounter) {
             if ($m[1] === null) {
                 ++$styleCounter;
             }
             return "{$m[2]}<a href=\"{$m[3]}\" class=\"style{$styleCounter}\">{$m[3]}</a>";
         },
         $string,
         -1,
         $count,
         PREG_UNMATCHED_AS_NULL
     );
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