When using regular expressions with PHP one must take care of a few minute details.
For instance, today I received a request to debug an application.
$patterns[0] = "/^Top/";
$replacements[0] = 'bear';
$text=" Top/Top/Top/Business/Top/Accounting/Top";
$text = preg_replace($patterns, $replacements, $text);
echo $text . "\n\n";
Can you spot the problem?
Hint: running the above produces:
Top/Top/Top/Business/Top/Accounting/Top
Here is the solution: many people mistakenly interpret ^ as the start of the line when in fact it represents the start of the string.
Modifying the above regular expression to
$patterns[0] = "/^Top\//";
$replacements[0] = 'bear/';
$text="Top/Top/Top/Business/Top/Accounting/Top";
#$text = preg_replace("/^(Top\/)/", '__', $text);
$text = preg_replace($patterns, $replacements, $text);
echo $text;
produces:
# bear/Top/Top/Business/Top/Accounting/Top
which was the desired solution in this problem.
