试图在后台运行php脚本脚本

Question

I have a PHP script, which accesses a database table, which contain information about some large files which need to be downloaded. I intend to run this PHP script as a cron job, in an hourly basis, and each time it runs, it should do the following things:

1. Check if there are files need to be downloaded
2. If there are, execute a shell script, which emits a wget command, and starts the downloading of the file, in the background, and when ready, runs a second php script, which updates the db tables of the completion of the download, and get back the process id of this shell script, for later use
3. Check if there are files currently being downloaded, if there are, check their process id is still active, and if not, adjust the table so we know that an error occured somewhere in the download

The shell script works accordingly, if I run it from the console, everything works fine, I am getting back the process id of the shell script also in my php file, my problem is, that when the originating php file exists, the shell script it initiated stops also.

Here's the code I use in php to start the shell script:

function runProcess($command, &$output=array()) {
    $command =  $command . ' > /dev/null 2>&1 & echo $!';
    echo $command . "<BR>";
    return exec($command, $output);
}

/** excerpt from the class that does the processing */
$pid=runProcess("sh ".self::DOWNLOAD_FILE_SHELL." ".DEFAULT_DIR_WHOME." 1.xml ".$this->Parent->XMLPath, $output));
echo $pid;

My question is as follows: How can I force the shell script to continue running, even when the parent process (the php script) exits?

Answer 1

If you're running on UNIX like environment, then the simplest way is to add ampersand (&) sign at the end of command line. this will tell the shell to run the command and not wait the completion. try this:

$command =  $command . ' > /dev/null 2>&1 & echo $! &';