The termination status, as pointed out in another note, is not the same as the exit status from the process. However, something like "pclose($fp)/256" is not the correct way to extract the exit status, since this uses system- and version-specific knowledge of where in the termination status the exit status is stored. (Also, the process may not even have exited normally, so it may not have an exit status at all.)
Instead, the functions pcntl_wifexited() and pcntl_wexitstatus() should be used. They are wrappers for the C macros WIFEXITED() and WEXITSTATUS() that are designed for determining whether the process had an exit status and what that status was, respectively.
(PHP 4, PHP 5)
pclose — Fecha um processo de um ponteiro de arquivo
Fecha um ponteiro de arquivo a uma pipe aberta por popen().
O ponteiro de arquivo tem que ser válido e tem que ser retornado por uma chamada bem sucedida a função popen().
Retorna o status da finalização do processo que estava executando.
- popen() - Abre um processo como ponteiro de arquivo
Warning: If you're reading a command with infinite output, such as 'vmstat 2', pclose will cause the script to hang. This is because pclose waits for the command to exit, in order to return the exit status. If the process never exits, pclose never returns.
Somewhere between 4.1.1 and 4.2.3, the return value from pclose changed.
The exit status used to be in the second byte, so that the status would be (pclose($fp)/256).
It is now in the low-order byte, so the status is just pclose($fp).
As I understand pclose will return 0 (on every platform) in case popen could not execute the specified command.
Since popen only returns the status wether it was able to send a command and not wether it was succesfully executed. Only the returned value of pclose can be used to check wether a command could be executed.