PHP exec doesn't return output of external program

When using the PHP exec function to run an external program, the output of the program may not be immediately visible in the result returned by exec. This behavior can occur due to various reasons, including buffering of the program's output. To capture the output of the external program properly, you can follow these steps:

1. Use Output Parameters:

   The exec function in PHP allows you to provide an output parameter that will store the program's output. For example:

   phpCopy code
   $output = array();
   
   $returnCode = null;
   
   exec('your_command_here', $output, $returnCode);
   
   
   
   // $output now contains the output of the command
   
   // $returnCode contains the exit code of the command
   
   

   By using the output parameter, you can capture the program's output in the $output array.

2. Flush Output in the External Program:

   Sometimes, the external program may not flush its output properly due to buffering. To overcome this, you can add explicit flushing of output in your external program. For example, in a Python script, you can use the sys.stdout.flush() command to ensure that the output is immediately sent to the PHP process.

   If you don't have control over the external program's source code, you can try using the stdbuf command (if available) to modify the buffering behavior of the external program:

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   stdbuf -o0 your_command_here
   
   

   This command will disable the output buffering for the specified command.

3. Check Error Messages:

   Make sure to check if there are any error messages generated by the external program. You can capture the standard error stream separately using the 2>&1 redirection:

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   exec('your_command_here 2>&1', $output, $returnCode);
   
   

   This will capture both standard output and standard error streams into the $output array.

If you're still experiencing issues capturing the output of the external program, consider checking if the external program is indeed producing output, whether it's buffering the output, and whether there are any error messages that might help diagnose the problem.