passthru hangs if the executed command writes to the clipboard

Question

Put this in a file "a.php" and execute it. It works just fine:

#!/usr/bin/php
<?php
$p = popen('xclip -i -selection clipboard', 'w');
fwrite($p, 'Hello Word');
pclose($p);

Now make a file "b.php" and execute it:

#!/usr/bin/php
<?php
passthru('./a.php');

It hangs forever. Why?

(If you do not have xclip, you can install it with apt-get install xclip)

Answer 1

"xclip -i -selection clipboard > /dev/null" should fix it

xclip doesn't close the STDOUT.

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