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Bug in preg_match() ?

php.internals

Michael Spector

22 years ago

Hi,

This script:

<?
$line = "Use operator m// for matching strings";
$pattern = "m//";

if(preg_match("/$pattern/", $line, $match)) {
print $match[0]."\n";
}
?>

outputs the following error:

<br />
<b>Warning</b>:  Unknown modifier '/' in <b>/home/michael/bug.php</b> on
line <b>5</b><br />


I thought it should find the match "m//" ...

Can you say, why search of the ending delimiter in a pattern cannot
be performed in a simple way, as you can see in the attached patch ?

Thanks.

Nuno Lopes

22 years ago

> Hi,
>
> This script:
>
> <?
>         $line = "Use operator m// for matching strings";
>         $pattern = "m//";
>
>         if(preg_match("/$pattern/", $line, $match)) {
>                 print $match[0]."\n";
>         }
> ?>

There is no bug here!

The final pattern is "/m///". When using // as delimeters, you must escape
them, so you would need to set
$pattern="m\/\/"

*or*
using other delimeter such as '~':
preg_match("~$pattern~",...)


Nuno

Curt Zirzow

22 years ago

* Thus wrote Michael Spector:

>
> Hi,
>
> This script:
>
> <?
>         $line = "Use operator m// for matching strings";
>         $pattern = "m//";
>
>         if(preg_match("/$pattern/", $line, $match)) {
>                 print $match[0]."\n";
>         }
> ?>
>
> outputs the following error:
>
> <br />
> <b>Warning</b>:  Unknown modifier '/' in <b>/home/michael/bug.php</b> on
> line <b>5</b><br />
>
>
> I thought it should find the match "m//" ...
>
> Can you say, why search of the ending delimiter in a pattern cannot
> be performed in a simple way, as you can see in the attached patch ?

Because of side effects like this:

$pattern = "Foo//i";
if(preg_match("/$pattern", $line, $match)) {

With your patch the preg_match has silently turned into a
caseINsensitve search.

Just use preg_quote($pattern, '/');

Curt

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