Today I was using the PHP command exec() in a script, which runs whatever you pass to it as it you had typed it on the command line. Its possible to check both the output of the command and the return value, which I did since I wasn’t getting the results I expected.
When you look at the output of the exec call, it isn’t the same as what you would see on the screen when typing the command. PHP returns you the content from stdout, but if anything goes wrong it will go to stderr which PHP doesn’t provide.
Redirect stdout to stderr
To get around this problem I altered my call from this:
exec ('unzip '.escapeshellarg($filename));
exec('unzip '.escapeshellarg($filename).' 2>&1);
This collection of characters tacked on the end of the code tells the system to send output 2 (stderr) to the address of output 1 (stdout). And the upshot is that I started to see the error messages being returned by the unzip program.
Not really relevant to my point but probably useful for reference – the actual problem was that unzip was returning 50 as its return value. This apparently means the disk is full, which it wasn’t.
What had happened was that I was unzipping a file in another directory and unzip was trying to place the contents into my current working directory rather than the one with the zip file in! I used the -d switch to unzip to direct the inflated files to the right place and this worked a treat.