Writing to the PHP error_log with var_dump & print_r

Writing objects to the PHP error log using error_log() can be useful, but it isn’t allowed – you can only write strings there. What to do?

Well, luckily there are options for both print_r() – human friendly – and var_dump() – parseable – that will let you convert an object into a string.

Use print_r()

Using print_r() is the easiest, since the second parameter to the function says that we want to send the output to a variable rather than echoing it. Thus, to write to the error_log you just need to use the following code.

Use var_dump()

If you want the more detailed output of var_dump(), it’s a bit trickier, but still pretty easy. In a nutshell, since you can only echo the results you have to capture the output buffer with ob_start(), assign it to a variable, and then clean the buffer with ob_end_clean() allowing you to write the resulting variable to the error_log.

function var_error_log( $object=null ){
    ob_start();                    // start buffer capture
    var_dump( $object );           // dump the values
    $contents = ob_get_contents(); // put the buffer into a variable
    ob_end_clean();                // end capture
    error_log( $contents );        // log contents of the result of var_dump( $object )

$object = new MyObject();
var_error_log( $object );

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13 Responses

  1. Pothi says:

    Thanks so much. Wanted to output the response headers for the a WordPress function (wp_remote_get). Can’t find better way than this.

  2. james says:

    great stuff. this is a major help.

  3. Dan Doran says:

    Nice write-up! Perhaps another option for your readers: When I need the OOP-related detail of var_dump, then I tend to use:

    error_log(var_export($message, true));

  4. This is great stuff, thank you very much for sharing!

  5. ravi says:

    thanks for sharing your knowledge! cheers

  6. Rafael says:

    Nice! Saved on my favorites! thanks!

  7. Robert Alexander says:

    This is a question that was brought up in my Programing Fundamentals class

    when should you use a var_dump and when should you use a print_r
    could someone help me understand it.

  8. jestine_coats says:

    Hello! I’ve been following your blog for a long time
    now and finally got the courage to go ahead and give you a shout
    out from Atascocita Texas! Just wanted to mention keep up the good job!

  9. Stoffo says:

    Hey man,
    very cool and simple trick, helped me a lot recently 🙂

  10. Mike iLL says:

    Very cool, man. To be honest, I’m having trouble finding the error_log. Is it supposed to create a folder and/or file in wp-content when debug is set to true? No – there it is – it just writes it to the php error log as set in php.ini.

    • User Avatar Justin Silver says:

      Anything you send to error_log() ends up in the PHP error log, but the location of that depends on how you have your server configured. It is usually something like /var/log/httpd/error.log for Apache, /var/log/nginx/error.log for Nginx. If you are using Windows or OSX it will depend on your config.

  1. April 8, 2015

    […] Credit goes to: justinsilver.com […]

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