Suppressing output from exec() calls in PHP

Question

I have a number of command line scripts in PHP that use exec() to perform tasks such as restarting services, loading MySQL timezone files, etc. While exec() itself does not output anything to the screen, some of the commands I am running are forcing output that I can't seem to suppress (even with ob_start()/ob_end_clean()). For example, the following would load timezone files into MySQL. We run this periodically to make sure MySQLs timezone data is up to date:

 $command = 'mysql_tzinfo_to_sql /usr/share/zoneinfo | mysql mysql';
 exec($command, $output, $result);

In this example, I would expect all output from the command to be written into $output, but I still get the following output forced to the screen:

Warning: Unable to load '/usr/share/zoneinfo/Asia/Riyadh87' as time zone. Skipping it.
Warning: Unable to load '/usr/share/zoneinfo/Asia/Riyadh88' as time zone. Skipping it.
Warning: Unable to load '/usr/share/zoneinfo/Asia/Riyadh89' as time zone. Skipping it.
...

Is there any way to suppress this output? Redirecting to /dev/null is not ideal as that would cause PHP to continue processing without waiting for the command to complete.

Thanks in advance,
~ JamesArmes

Answer 1

Redirecting stderr alone should not influence where processing takes place, just make sure not to add an &. It should only run in the background if you redirect the output and make it run in the background.

Edit:

Cracked open cygwin, you need to redirect stderr for the first command, give this a try:

$command = 'mysql_tzinfo_to_sql /usr/share/zoneinfo 2> /dev/null | mysql mysql';
exec($command, $output, $result);

Answer 2

Just redirect stderr to /dev/null

$command = 'mysql_tzinfo_to_sql /usr/share/zoneinfo | mysql mysql 2>/dev/null';

or to stdout

$command = 'mysql_tzinfo_to_sql /usr/share/zoneinfo | mysql mysql 2>&1';

Answer 3

Redirecting to /dev/null does not cause PHP to stop waiting for the command. Adding a & does do this, you probably associate the two because the final & is often used in conjunction with a redirect.

In response to Yannick's (deleted) comment: it seems if you want to run something in the background in PHP, you must redirect as well as using &. This does not mean that redirection alone causes it to run in the background.

Answer 4

According to http://us3.php.net/manual/en/function.shell-exec.php you can assign this command's output to a variable.

You don't necessarily have to do anything with the variable, which means you are effectively suppressing output.

Hope that helps!