Checking pattern as much as possible - php

Question

How to make preg find all possible solutions for regular expression pattern?
Here's the code:
<?php
$text = 'Amazing analyzing.';
$regexp = '/(^|\\b)([\\S]*)(a)([\\S]*)(\\b|$)/ui';
$matches = array();
if (preg_match_all($regexp, $text, $matches, PREG_SET_ORDER)) {
foreach ($matches as $match) {
echo "{$match[2]}[{$match[3]}]{$match[4]}\n";
}
}
?>
Output:
Am[a]zing
an[a]lyzing.
Output that i need:
[A]mazing
Am[a]zing
[A]nalyzing.
an[a]lyzing.

Answer 1

You have to use look behind/ahead zero-length assertions (instead of a normal pattern which consumes the characters around what your are looking for): http://www.regular-expressions.info/lookaround.html

Answer 2

Lookaround assertions won't help, for two reasons:
Since they are zero-length, they won't return characters that you need.
As Avinash Raj noted, PHP lookbehind doesn't allow *.
This yields the output that you need:
<?php
$text = 'Amazing analyzing.';
foreach (preg_split('/\s+/', $text) as $word)
{
$matches = preg_split('/(a)/i', $word, 0, PREG_SPLIT_DELIM_CAPTURE);
for ($match = 1; $match < count($matches); $match += 2)
{
$prefix = join(array_slice($matches, 0, $match));
$suffix = join(array_slice($matches, $match+1));
echo "{$prefix}[{$matches[$match]}]{$suffix}\n";
}
}
?>