How to retrieve PHP exec() error responses?

php shell exec
Matt picture Matt · Dec 6, 2008 · Viewed 55.6k times · Source

Below is the command I tried executing, without success:

exec('ln -s ' . PLUGIN_DIR . '/.htaccess ' . ABSPATH . '/.htaccess');

When you add a die() at the end, it catches that there's an error:

exec('ln -s ' . PLUGIN_DIR . '/.htaccess ' . ABSPATH . '/.htaccess') or die('what?!');

For the above exec() statement, a permissions problem is causing the error, but PHP isn't displaying it. How do you display from PHP what error is occurring?

Answer

S.ov picture S.ov · Jun 6, 2014

The $output parameter does not appear to work if the calling program spits output to STDERR.

A better way to handle this is to redirect the output from exec to a file and then display the contents of that file if there is an error condition.

If $cmd holds the exec command add something like this:

$cmd.=" > $error_log 2>&1"

Then examine the contents of the filespec in $error_log for detailed info on why the command failed.

Also note that if you fork this off with a & at the end of the command, an immediate check of the contents of $error_log may not reveal the log information - the script may check/process the file before the OS has finished.

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