A question about redirection in PHP

For an example, link A to "www.abc.com/test.php?#if eregi ('ABC', $ _ SERVER ['http _ referer']) | strpos ($ _ SERVER ['http _ host'], 'ABC ')! = Fal: a question about redirection in PHP
For example, link A to "www.abc.com/test.php"
Determine if eregi ('ABC', $ _ SERVER ['http _ referer']) | strpos ($ _ SERVER ['http _ host'], 'ABC ')! = False
Go to www.def.com/test.php.

The local test is successful, but the two URLs are repeatedly redirected on the SERVER. then, the strpos ($ _ SERVER ['http _ host'], 'ABC') is removed ')! = False.
Why?

In addition, the redirection method I use is
Echo' '; Exit;
Others are normal, but the Apple browser does not seem to work .. ..


Is there a better way? I have tried a lot before, but it seems to have something to do with browsers, for example, to output headers and javascript?


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You can

Header ("location: www.def.com/test.php ");


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Abc and def are just different domain names, and the directories and files to which they are directed are the same.
This is the key. The operation is actually the same file.
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I don't know if it is the same file ~~ Solution ~~