RegExp weirdness

[jscheuer1]

Consider this:

<?php
$theBack = $_SERVER["HTTP_REFERER"];
$thePat1 = "/^http:\/(\/www\.)|(\/)some\.com/";
$thePat2 = "/^(http:\/\/some\.com)|(http:\/\/www\.some\.com)/";
if(eregi($thePat1, $theBack))
echo $theBack . ' pat one';
if(eregi($thePat2, $theBack))
echo $theBack . ' pat two';
?>

Shouldn't these two patterns match the same strings:

http://www.some.com/whatever

and:

http://some.com/whatever

If not, why not?

In my test environment, thePat1 matches http://some.com and thePat2 matches http://www.some.com

The result being that I'm not 100% sure that either can be relied upon to exclude other domains. Is there a better approach to this. I just want to make sure that the referring document is from the same domain before writing out a back button to that page.

[JasonDFR]

$theBack = 'http://www.|/some.com/'; // Matches pat1 also

I'll try to work out one pattern that matches both later. I think that when using the | pipe you need to be inside parenthesis.

For example:

(this | that) // not (this) | (that)

I'm no regex expert, but I love trying to figure them out.

Just to be clear, you would like one regex that matches both http://some.com and http://www.some.com ?

[JasonDFR]

I came up with this:

<?php

$match = 'http://some.com/';

$pat = '/^http:\/\/(www.|)some.com\//';

if ( preg_match($pat, $match) ) {
    echo 'Match!<br>';
    echo 'Pat: ' . $pat . '<br>';
    echo 'Match: ' . $match;
} else {
    echo 'no match';
}

exit;

As always I would love to see other regexs. Especially if they are more elegant. hehe...

jscheuer, let me know if this works for you. And BTW, use preg, not ereg.

[Schmoopy]

So the "(www.|)" is like saying "www." or "" right? Either this or nothing?

[Master_script_maker]

yes (www\.|) is like (www\.)?

Edit: Added below:

Here is a useful little code snippet to test regexs. You can add as many regexs as you want:

$pat=Array(
"com"=> "/^(http:\/\/)?(www\.)?([^.]*?)\.com/",
"s com"=> "/^(http(s)?:\/\/)?(www\.)?([^.]*?)\.com/",
"sub"=> "/^(http(s)?:\/\/)?(www\.)?([^.]*?\.)?([^.]*?)\.com/",
"multiple domain"=> "/^(http(s)?:\/\/)?(www\.)?([^.]*\.)?([^.]*?)(\..{2}\..{2}|\..{3})/"
);
$padding="  ";
$string="https://bob.site.co.uk";

echo "String: <strong>".$string."</strong><br><br>";

foreach($pat as $k=>$v) {
  $pad=$padding;
  echo 'Pattern <strong>'.$k.'</strong> <em>' . $v . '</em><br>'.$pad;
  if ( preg_match($v, $string, $matches) ) {
    echo 'Match: ';
    echo cust_print($matches, $pad, 2);
  } else {
    echo 'No Match';
  }
  echo "<br><br>";
}

function cust_print($a, $p="", $n=1) {
  if(!is_array($a)) {
    return $a;
  }
  $s="Array(";
  foreach($a as $k=>$v) {
    $s.="<br>".str_repeat($p, $n).'['.$k.'] => '.cust_print($v, $p, $n+1);
  }
  $s.="<br>".str_repeat($p, $n-1).")";
  return $s;
}

[jscheuer1]

This is all pretty much nonsense or at least inefficient to me. In javascript we can just do:

<script type="text/javascript">
var dr = 'http://www.some.com/whatever.htm',
r = new RegExp('^http:\\/(\\/www\\.|\\/)some\\.com');
alert(r.test(dr)); //alerts true
dr = 'http://some.com/whatever.htm'
alert(r.test(dr)); //alerts true
dr = 'http://www.someother.com/whatever.htm'
alert(r.test(dr)); //alerts false
dr = 'http://someother.com/whatever.htm'
alert(r.test(dr)); //alerts false
</script>

Is there no equivalent in PHP?

If I have the document.referrer string as the var dr, a simple test of either one of these (not both - only one of them is required - it's just that either will work):

/^http:\/(\/www\.|\/)some\.com/.test(dr)

or:

/^http:\/(\/www\.)|(\/)some\.com/.test(dr)

will tell me if it comes from the some.com domain or not. There must be something equally as simple in PHP, perhaps even simpler, as In many cases PHP is simpler than javascript - perhaps something as simple as:

isSameDomain($_SERVER["HTTP_REFERER"])

Is there no equivalent of the javascript test() method in PHP - or better yet - a more efficient way of telling if a given URL comes from the same domain as the present page?

[Nile]

I guess there is, although I don't know much about reg exp. You could use preg_match, if the value is 0, then it will not be true.

[jscheuer1]

You guess? What a wimpy answer! Anyways, I found this rather simple approach after much trial and error:

<?php
$thePat = '^http://' . $_SERVER['HTTP_HOST'];
$theBack = $_SERVER['HTTP_REFERER'];
if (ereg($thePat, $theBack))
echo $theBack;
else
echo 'other domain';
?>

I'm thinking I will either echo a link back to the previous page ($_SERVER["HTTP_REFERER"]) or (if the test fails) include a file that has a menu of various on site pages that might be appropriate choices. I'm just wondering if there is anything that looks unworkable/dangerous/stupid/etc. here or not.

[jscheuer1]

Perhaps even more to the point:

<?php 
$theHost = $_SERVER['HTTP_HOST']; 
$theBack = $_SERVER['HTTP_REFERER']; 
$theBParse = parse_url($theBack);

if ($theBParse['host'] == $theHost)
echo $theBack; // or do whatever if referrer is from the same domain
else 
echo 'other domain'; // or do whatever if the referrer is from another domain
?>

As I said, this sort of thing is usually simpler in PHP than in javascript, which is why I couldn't understand how complicated the answers were getting.

[Twey]

The thing to consider is that | has a very low operator precedence — that's why you usually see an alternative enclosed in brackets.

$thePat1 = "/^http:\/(\/www\.)|(\/)some\.com/";

'Match either "http://www." at the start of the string, or "/some.com" anywhere in the string.'

$thePat2 = "/^(http:\/\/some\.com)|(http:\/\/www\.some\.com)/";

'Match either the start of the string followed by "http://some.com" or "http://www.some.com/" anywhere in the string.'