php : Capturing the command output

All we need is an easy explanation of the problem, so here it is.

I am using exec function to execute the specific executable files in php .

exec ( $file , $output , $return_value  ) ;

When the given file executed successfully I am able to get the output in the second argument
by checking the return values , So, It is working fine. But My requirement is when the command execution getting failed due to some reason. I need to get that error message of that executed program . What I need to do to get the error . through second argument we can get the successful output only . Not error message.


How to solve :

I know you bored from this bug, So we are here to help you! Take a deep breath and look at the explanation of your problem. We have many solutions to this problem, But we recommend you to use the first method because it is tested & true method that will 100% work for you.

Method 1

The second argument $output only captures STDOUT from your executable. Error messages are usually sent to STDERR so that they easily can be written to an error log or similar, but this means that you won’t see them when you call exec.

If this is a linux system, you could append 2>&1 to your command, in order to redirect STDERR to STDOUT. I haven’t tried this, but it should forward the error messages to your $output variable.


I’ve read up on it on, and it seems this would work.

exec($file.' 2>&1', $outputAndErrors, $return_value);

It is also possible to redirect the errors to a temporary file and read them separately.

exec($file.' 2> '.$tmpFile, $outputOnly, $return_value);

Edit 2

It seems windows also uses this Bourne style output redirecting syntax, so the examples should work for windows too.

More on input and output streams

Method 2

If you need to keep stderr and stdout separate, try proc_open:

Method 3

The $return_value will have the error code returned by the program which should be meaningfull enough, I don’t think you can have better.

Note: Use and implement method 1 because this method fully tested our system.
Thank you 🙂

All methods was sourced from or, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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