Conditional string replace

Question

I have a funcion which is somthing like this :

function replaceXMLEntities($subject) {
 $subject = str_replace("&", "&amp;", $subject);
 $subject = str_replace("'", "&apos;", $subject);
 $subject = str_replace("<", "&lt;", $subject);
 $subject = str_replace(">", "&gt;", $subject);
 $subject = str_replace("\"", "&quot;", $subject);

 return $subject;
}

This function is used to convert strings to a safe string for xmpl encoding.

But i have a problem in which casses some xmpl data ges encoded 2 times, like

&amp;

as imput gets to

&&amp;

Just like in here when you enter the text without code quote :)

I need a regex which could distinguish between & and & somthing like

if not &amp then do & -> &amp; conversion else dont touch it.

Any idea how i could achive such regex? I could go and make a funciton but in this case a regex is clearly a better option.

arychj · Accepted Answer · 2013-06-27 13:50:27Z

1

$subject = preg_replace('#(?!&)&#', '&', $subject);

Though using htmlspecialchars() might be easier...

answered Jun 27, 2013 at 13:50

arychj

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Mixthos · Accepted Answer · 2013-06-27 13:43:34Z

1

You could achieve the same without a regular expression by replacing all &amps with & first:

$subject = str_replace("&amp;", "&", $subject);

answered Jun 27, 2013 at 13:43

Mixthos

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1 Comment

Sangoku Over a year ago

Simple but briliant thy :3

Wesley Schleumer de Góes · Accepted Answer · 2013-06-27 14:02:45Z

0

Hardcore way:

preg_replace('/&(?!#?[a-z0-9]+;)/', '&amp;', '&amp; & &lt; &gt;');

Easy and right way is using htmlspecialchars().

answered Jun 27, 2013 at 14:02

Wesley Schleumer de Góes

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Comments

HamZa · Accepted Answer · 2013-06-27 14:15:51Z

Pretty simple using preg_replace()^regex:
$subject = preg_replace('&(?!amp;)', '', $subject);

&: match & (?!amp;): Negative lookahead, check if there is no amp;

We'll still use str_replace() for the other characters, but note that it supports several inputs/replacements, so our final code will be:

function replaceXMLEntities($subject){
    $subject = preg_replace('&(?!amp;)', '', $subject);
    $subject = str_replace(array("'", '<', '>', '"'), array('&apos;', '&lt;', '&gt;', '&quot;'), $subject);

    return $subject;
}

You could also use a tricky way, first replace all & with & and then replace all & with &:

function replaceXMLEntities($subject){
    return str_replace(array('&amp;', '&', "'", '<', '>', '"'), array('&', '&amp;', '&apos;', '&lt;', '&gt;', '&quot;'), $subject);
}

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