$re = '/\[(\w*)\]\n/';
$str = '[HEADER1]
{
key value
key value
...
[HEADER2]
{
key value
...
}
key value
[HEADER3]
{
key value
[HEADER4]
{
key value
...
}
}
key value
}
';
$subst = "\"$1\":";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php