Question

I wrote this code:

<?
$text='how are you [b] today [/b]';
$patterns = array();
$patterns[0] = '/\[b/';
$patterns[1] = '/\b]/';
$replacements = array();
$replacements[1] = 'b]aaa<>';
$replacements[0] = '<>aaa[b';


ksort($patterns);
ksort($replacements);
echo preg_replace($patterns, $replacements, $text);
echo "_";
echo $text;
echo "_";
echo "END";

?>

the output shows:

how are you <>aaa[bb]aaa<> today [/b]aaa<>______how are you [b] today [/b]______END

but the output should be:

how are you <>aaa[b] today [/b]aaa<>______how are you [b] today [/b]______END

what did I do wrong? Please help. Thank you

Answer 1

You need to double-escape the brackets:

$patterns[0] = '/\\[b/';

A single backslash will be “consumed” by PHP when it parses the string, leaving just a bare [, which will be seen by the regex engine as the beginning of a character class. By double-escaping, the \\ will be seen by PHP as an escape, leaving a single \, which will be seen by the regex engine as an escape.